diff --git a/core/src/main/java/org/everit/json/schema/AbstractFormatValidator.java b/core/src/main/java/org/everit/json/schema/AbstractFormatValidator.java
new file mode 100644
index 000000000..8433fd691
--- /dev/null
+++ b/core/src/main/java/org/everit/json/schema/AbstractFormatValidator.java
@@ -0,0 +1,66 @@
+package org.everit.json.schema;
+
+import static java.util.Objects.requireNonNull;
+
+import java.util.Map;
+import java.util.Optional;
+
+import org.everit.json.schema.internal.DateTimeFormatValidator;
+import org.everit.json.schema.internal.EmailFormatValidator;
+import org.everit.json.schema.internal.HostnameFormatValidator;
+import org.everit.json.schema.internal.IPV4Validator;
+import org.everit.json.schema.internal.IPV6Validator;
+import org.everit.json.schema.internal.URIFormatValidator;
+
+/**
+ * Implementations perform the validation against the "format" keyword (see JSON Schema spec section
+ * 7).
+ */
+public interface AbstractFormatValidator {
+    
+    /**
+     * Implementation-specific validation of {@code subject}. If a validation error occurs then
+     * implementations should return a programmer-friendly error message as a String wrapped in an
+     * Optional. If the validation succeeded then {@link Optional#empty() an empty optional} should be
+     * returned.
+     *
+     * @param subject
+     *         the string to be validated
+     * 
+     * @return an {@code Optional} wrapping the error message if a validation error occured, otherwise
+     * {@link Optional#empty() an empty optional}.
+     */
+    Optional<String> validate(String subject);
+
+    /**
+     * Implementation-specific validation of {@code subject}. If a validation error occurs then
+     * implementations should return a programmer-friendly error message as a String wrapped in an
+     * Optional. If the validation succeeded then {@link Optional#empty() an empty optional} should be
+     * returned.
+     *
+     * @param subject
+     *         the string to be validated
+     * @param unprocessedProperties
+     *         the map of unprocessed properties, which can be useful for some custom complex format
+     * 
+     * @return an {@code Optional} wrapping the error message if a validation error occured, otherwise
+     * {@link Optional#empty() an empty optional}.
+     */
+    Optional<String> validate(String subject, Map<String, Object> unprocessedProperties);
+
+    /**
+     * Provides the name of this format.
+     * <p>
+     * Unless specified otherwise the {@link org.everit.json.schema.loader.SchemaLoader} will use this
+     * name to recognize string schemas using this format.
+     * </p>
+     * The default implementation of this method returns {@code "unnamed-format"}. It is strongly
+     * recommended for implementations to give a more meaningful name by overriding this method.
+     *
+     * @return the format name.
+     */
+    default String formatName() {
+        return "unnamed-format";
+    }
+
+}
diff --git a/core/src/main/java/org/everit/json/schema/ContextualFormatValidator.java b/core/src/main/java/org/everit/json/schema/ContextualFormatValidator.java
new file mode 100644
index 000000000..0d772682b
--- /dev/null
+++ b/core/src/main/java/org/everit/json/schema/ContextualFormatValidator.java
@@ -0,0 +1,38 @@
+package org.everit.json.schema;
+
+import static java.util.Objects.requireNonNull;
+
+import java.util.Map;
+import java.util.Optional;
+
+import org.everit.json.schema.internal.DateTimeFormatValidator;
+import org.everit.json.schema.internal.EmailFormatValidator;
+import org.everit.json.schema.internal.HostnameFormatValidator;
+import org.everit.json.schema.internal.IPV4Validator;
+import org.everit.json.schema.internal.IPV6Validator;
+import org.everit.json.schema.internal.URIFormatValidator;
+
+/**
+ * Implementations perform the validation against the "format" keyword (see JSON Schema spec section
+ * 7).
+ */
+@FunctionalInterface
+public interface ContextualFormatValidator extends AbstractFormatValidator {
+
+    /**
+     * Implementation-specific validation of {@code subject}. If a validation error occurs then
+     * implementations should return a programmer-friendly error message as a String wrapped in an
+     * Optional. If the validation succeeded then {@link Optional#empty() an empty optional} should be
+     * returned.
+     *
+     * @param subject
+     *         the string to be validated
+     * 
+     * @return an {@code Optional} wrapping the error message if a validation error occured, otherwise
+     * {@link Optional#empty() an empty optional}.
+     */
+    default Optional<String> validate(String subject) {
+        return validate(subject,null);
+    }
+
+}
diff --git a/core/src/main/java/org/everit/json/schema/FormatValidator.java b/core/src/main/java/org/everit/json/schema/FormatValidator.java
index 718743f7f..e3fd6c3f0 100644
--- a/core/src/main/java/org/everit/json/schema/FormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/FormatValidator.java
@@ -2,6 +2,7 @@
 
 import static java.util.Objects.requireNonNull;
 
+import java.util.Map;
 import java.util.Optional;
 
 import org.everit.json.schema.internal.DateTimeFormatValidator;
@@ -16,12 +17,12 @@
  * 7).
  */
 @FunctionalInterface
-public interface FormatValidator {
+public interface FormatValidator extends AbstractFormatValidator {
 
     /**
      * No-operation implementation (never throws {always returns {@link Optional#empty()}).
      */
-    FormatValidator NONE = subject -> Optional.empty();
+    FormatValidator NONE = (subject) -> Optional.empty();
 
     /**
      * Static factory method for {@code FormatValidator} implementations supporting the
@@ -67,24 +68,14 @@ static FormatValidator forFormat(final String formatName) {
      *
      * @param subject
      *         the string to be validated
+     * @param unprocessedProperties
+     *         the map of unprocessed properties, which can be useful for some custom complex format
+     * 
      * @return an {@code Optional} wrapping the error message if a validation error occured, otherwise
      * {@link Optional#empty() an empty optional}.
      */
-    Optional<String> validate(String subject);
-
-    /**
-     * Provides the name of this format.
-     * <p>
-     * Unless specified otherwise the {@link org.everit.json.schema.loader.SchemaLoader} will use this
-     * name to recognize string schemas using this format.
-     * </p>
-     * The default implementation of this method returns {@code "unnamed-format"}. It is strongly
-     * recommended for implementations to give a more meaningful name by overriding this method.
-     *
-     * @return the format name.
-     */
-    default String formatName() {
-        return "unnamed-format";
+    default Optional<String> validate(String subject, Map<String, Object> unprocessedProperties) {
+        return validate(subject);
     }
 
 }
diff --git a/core/src/main/java/org/everit/json/schema/StringSchema.java b/core/src/main/java/org/everit/json/schema/StringSchema.java
index 68ea7099d..6096a87db 100644
--- a/core/src/main/java/org/everit/json/schema/StringSchema.java
+++ b/core/src/main/java/org/everit/json/schema/StringSchema.java
@@ -27,7 +27,7 @@ public static class Builder extends Schema.Builder<StringSchema> {
 
         private boolean requiresString = true;
 
-        private FormatValidator formatValidator = NONE;
+        private AbstractFormatValidator formatValidator = NONE;
 
         @Override
         public StringSchema build() {
@@ -43,7 +43,7 @@ public StringSchema build() {
          *         the format validator
          * @return {@code this}
          */
-        public Builder formatValidator(final FormatValidator formatValidator) {
+        public Builder formatValidator(final AbstractFormatValidator formatValidator) {
             this.formatValidator = requireNonNull(formatValidator, "formatValidator cannot be null");
             return this;
         }
@@ -86,7 +86,7 @@ public static Builder builder() {
 
     private final boolean requiresString;
 
-    private final FormatValidator formatValidator;
+    private final AbstractFormatValidator formatValidator;
 
     public StringSchema() {
         this(builder());
@@ -149,7 +149,7 @@ public boolean equals(Object o) {
         }
     }
 
-    public FormatValidator getFormatValidator() {
+    public AbstractFormatValidator getFormatValidator() {
         return formatValidator;
     }
 
diff --git a/core/src/main/java/org/everit/json/schema/StringSchemaValidatingVisitor.java b/core/src/main/java/org/everit/json/schema/StringSchemaValidatingVisitor.java
index c32ebbe65..7e6adf4e4 100644
--- a/core/src/main/java/org/everit/json/schema/StringSchemaValidatingVisitor.java
+++ b/core/src/main/java/org/everit/json/schema/StringSchemaValidatingVisitor.java
@@ -51,8 +51,8 @@ public StringSchemaValidatingVisitor(Object subject, ValidatingVisitor owner) {
         }
     }
 
-    @Override void visitFormat(FormatValidator formatValidator) {
-        Optional<String> failure = formatValidator.validate(stringSubject);
+    @Override void visitFormat(AbstractFormatValidator formatValidator, Schema schema) {
+        Optional<String> failure = formatValidator.validate(stringSubject, schema.getUnprocessedProperties());
         if (failure.isPresent()) {
             owner.failure(failure.get(), "format");
         }
diff --git a/core/src/main/java/org/everit/json/schema/Visitor.java b/core/src/main/java/org/everit/json/schema/Visitor.java
index 18d5d12a9..a9843526a 100644
--- a/core/src/main/java/org/everit/json/schema/Visitor.java
+++ b/core/src/main/java/org/everit/json/schema/Visitor.java
@@ -167,10 +167,10 @@ void visitStringSchema(StringSchema stringSchema) {
         visitMinLength(stringSchema.getMinLength());
         visitMaxLength(stringSchema.getMaxLength());
         visitPattern(stringSchema.getRegexpPattern());
-        visitFormat(stringSchema.getFormatValidator());
+        visitFormat(stringSchema.getFormatValidator(),stringSchema);
     }
 
-    void visitFormat(FormatValidator formatValidator) {
+    void visitFormat(AbstractFormatValidator formatValidator, Schema schema) {
     }
 
     void visitPattern(Regexp pattern) {
diff --git a/core/src/main/java/org/everit/json/schema/internal/DateTimeFormatValidator.java b/core/src/main/java/org/everit/json/schema/internal/DateTimeFormatValidator.java
index db083fd63..ef8519189 100644
--- a/core/src/main/java/org/everit/json/schema/internal/DateTimeFormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/DateTimeFormatValidator.java
@@ -6,6 +6,7 @@
 import java.time.format.DateTimeFormatterBuilder;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Map;
 import java.util.Optional;
 
 import static org.everit.json.schema.internal.TemporalFormatValidator.SECONDS_FRACTION_FORMATTER;
diff --git a/core/src/main/java/org/everit/json/schema/internal/EmailFormatValidator.java b/core/src/main/java/org/everit/json/schema/internal/EmailFormatValidator.java
index edf4fc3fd..ec8d780cd 100644
--- a/core/src/main/java/org/everit/json/schema/internal/EmailFormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/EmailFormatValidator.java
@@ -1,5 +1,6 @@
 package org.everit.json.schema.internal;
 
+import java.util.Map;
 import java.util.Optional;
 
 import org.apache.commons.validator.routines.EmailValidator;
diff --git a/core/src/main/java/org/everit/json/schema/internal/HostnameFormatValidator.java b/core/src/main/java/org/everit/json/schema/internal/HostnameFormatValidator.java
index 70ce2853b..0d06d9750 100644
--- a/core/src/main/java/org/everit/json/schema/internal/HostnameFormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/HostnameFormatValidator.java
@@ -3,6 +3,7 @@
 import org.apache.commons.validator.routines.DomainValidator;
 import org.everit.json.schema.FormatValidator;
 
+import java.util.Map;
 import java.util.Optional;
 
 /**
diff --git a/core/src/main/java/org/everit/json/schema/internal/IPV4Validator.java b/core/src/main/java/org/everit/json/schema/internal/IPV4Validator.java
index 7871aaed1..b44ad0108 100644
--- a/core/src/main/java/org/everit/json/schema/internal/IPV4Validator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/IPV4Validator.java
@@ -3,6 +3,7 @@
 import org.apache.commons.validator.routines.InetAddressValidator;
 import org.everit.json.schema.FormatValidator;
 
+import java.util.Map;
 import java.util.Optional;
 
 /**
diff --git a/core/src/main/java/org/everit/json/schema/internal/IPV6Validator.java b/core/src/main/java/org/everit/json/schema/internal/IPV6Validator.java
index ad629a1df..034a50500 100644
--- a/core/src/main/java/org/everit/json/schema/internal/IPV6Validator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/IPV6Validator.java
@@ -3,6 +3,7 @@
 import org.apache.commons.validator.routines.InetAddressValidator;
 import org.everit.json.schema.FormatValidator;
 
+import java.util.Map;
 import java.util.Optional;
 
 /**
diff --git a/core/src/main/java/org/everit/json/schema/internal/JsonPointerFormatValidator.java b/core/src/main/java/org/everit/json/schema/internal/JsonPointerFormatValidator.java
index 7a862363b..ca9287002 100644
--- a/core/src/main/java/org/everit/json/schema/internal/JsonPointerFormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/JsonPointerFormatValidator.java
@@ -2,6 +2,7 @@
 
 import static java.lang.String.format;
 
+import java.util.Map;
 import java.util.Optional;
 
 import org.everit.json.schema.FormatValidator;
diff --git a/core/src/main/java/org/everit/json/schema/internal/RegexFormatValidator.java b/core/src/main/java/org/everit/json/schema/internal/RegexFormatValidator.java
index 28fac7481..cc9c77085 100644
--- a/core/src/main/java/org/everit/json/schema/internal/RegexFormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/RegexFormatValidator.java
@@ -1,5 +1,6 @@
 package org.everit.json.schema.internal;
 
+import java.util.Map;
 import java.util.Optional;
 import java.util.regex.Pattern;
 import java.util.regex.PatternSyntaxException;
diff --git a/core/src/main/java/org/everit/json/schema/internal/RelativeJsonPointerFormatValidator.java b/core/src/main/java/org/everit/json/schema/internal/RelativeJsonPointerFormatValidator.java
index 8cefbb4a8..d008019a4 100644
--- a/core/src/main/java/org/everit/json/schema/internal/RelativeJsonPointerFormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/RelativeJsonPointerFormatValidator.java
@@ -1,5 +1,6 @@
 package org.everit.json.schema.internal;
 
+import java.util.Map;
 import java.util.Optional;
 
 import org.everit.json.schema.FormatValidator;
diff --git a/core/src/main/java/org/everit/json/schema/internal/TemporalFormatValidator.java b/core/src/main/java/org/everit/json/schema/internal/TemporalFormatValidator.java
index 3b679c9c7..be06a126c 100644
--- a/core/src/main/java/org/everit/json/schema/internal/TemporalFormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/TemporalFormatValidator.java
@@ -6,6 +6,8 @@
 import java.time.format.DateTimeFormatterBuilder;
 import java.time.format.DateTimeParseException;
 import java.time.temporal.ChronoField;
+
+import java.util.Map;
 import java.util.Optional;
 
 import static java.util.Objects.requireNonNull;
diff --git a/core/src/main/java/org/everit/json/schema/internal/URIFormatValidator.java b/core/src/main/java/org/everit/json/schema/internal/URIFormatValidator.java
index 7adc6c2b3..05b04c61c 100644
--- a/core/src/main/java/org/everit/json/schema/internal/URIFormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/URIFormatValidator.java
@@ -2,6 +2,8 @@
 
 import java.net.URI;
 import java.net.URISyntaxException;
+
+import java.util.Map;
 import java.util.Optional;
 
 import org.everit.json.schema.FormatValidator;
diff --git a/core/src/main/java/org/everit/json/schema/internal/URIReferenceFormatValidator.java b/core/src/main/java/org/everit/json/schema/internal/URIReferenceFormatValidator.java
index bee1a13ea..5d0c49bb1 100644
--- a/core/src/main/java/org/everit/json/schema/internal/URIReferenceFormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/URIReferenceFormatValidator.java
@@ -4,6 +4,8 @@
 
 import java.net.URI;
 import java.net.URISyntaxException;
+
+import java.util.Map;
 import java.util.Optional;
 
 import org.everit.json.schema.FormatValidator;
diff --git a/core/src/main/java/org/everit/json/schema/internal/URITemplateFormatValidator.java b/core/src/main/java/org/everit/json/schema/internal/URITemplateFormatValidator.java
index e144161b7..6a3033b61 100644
--- a/core/src/main/java/org/everit/json/schema/internal/URITemplateFormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/URITemplateFormatValidator.java
@@ -2,6 +2,7 @@
 
 import static java.lang.String.format;
 
+import java.util.Map;
 import java.util.Optional;
 
 import org.everit.json.schema.FormatValidator;
diff --git a/core/src/main/java/org/everit/json/schema/internal/URIV4FormatValidator.java b/core/src/main/java/org/everit/json/schema/internal/URIV4FormatValidator.java
index 6cca1b4bd..4d0b74f2f 100644
--- a/core/src/main/java/org/everit/json/schema/internal/URIV4FormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/internal/URIV4FormatValidator.java
@@ -2,6 +2,7 @@
 
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.util.Map;
 import java.util.Optional;
 import org.everit.json.schema.FormatValidator;
 
diff --git a/core/src/main/java/org/everit/json/schema/loader/LoaderConfig.java b/core/src/main/java/org/everit/json/schema/loader/LoaderConfig.java
index dba904211..655d437ab 100644
--- a/core/src/main/java/org/everit/json/schema/loader/LoaderConfig.java
+++ b/core/src/main/java/org/everit/json/schema/loader/LoaderConfig.java
@@ -10,7 +10,7 @@
 import java.util.HashMap;
 import java.util.Map;
 
-import org.everit.json.schema.FormatValidator;
+import org.everit.json.schema.AbstractFormatValidator;
 import org.everit.json.schema.loader.internal.DefaultSchemaClient;
 import org.everit.json.schema.regexp.JavaUtilRegexpFactory;
 import org.everit.json.schema.regexp.RegexpFactory;
@@ -26,7 +26,7 @@ static LoaderConfig defaultV4Config() {
 
     final SchemaClient schemaClient;
 
-    final Map<String, FormatValidator> formatValidators;
+    final Map<String, AbstractFormatValidator> formatValidators;
 
     final Map<URI, Object> schemasByURI;
 
@@ -38,12 +38,12 @@ static LoaderConfig defaultV4Config() {
 
     final RegexpFactory regexpFactory;
 
-    LoaderConfig(SchemaClient schemaClient, Map<String, FormatValidator> formatValidators,
+    LoaderConfig(SchemaClient schemaClient, Map<String, AbstractFormatValidator> formatValidators,
             SpecificationVersion specVersion, boolean useDefaults) {
         this(schemaClient, formatValidators, emptyMap(), specVersion, useDefaults, false, new JavaUtilRegexpFactory());
     }
 
-    LoaderConfig(SchemaClient schemaClient, Map<String, FormatValidator> formatValidators,
+    LoaderConfig(SchemaClient schemaClient, Map<String, AbstractFormatValidator> formatValidators,
             Map<URI, Object> schemasByURI,
             SpecificationVersion specVersion, boolean useDefaults, boolean nullableSupport,
             RegexpFactory regexpFactory) {
diff --git a/core/src/main/java/org/everit/json/schema/loader/SchemaLoader.java b/core/src/main/java/org/everit/json/schema/loader/SchemaLoader.java
index 505586514..7afbc1201 100644
--- a/core/src/main/java/org/everit/json/schema/loader/SchemaLoader.java
+++ b/core/src/main/java/org/everit/json/schema/loader/SchemaLoader.java
@@ -21,7 +21,7 @@
 import org.everit.json.schema.CombinedSchema;
 import org.everit.json.schema.EmptySchema;
 import org.everit.json.schema.FalseSchema;
-import org.everit.json.schema.FormatValidator;
+import org.everit.json.schema.AbstractFormatValidator;
 import org.everit.json.schema.Schema;
 import org.everit.json.schema.SchemaException;
 import org.everit.json.schema.SchemaLocation;
@@ -58,7 +58,7 @@ public static class SchemaLoaderBuilder {
 
         SchemaLocation pointerToCurrentObj = SchemaLocation.empty();
 
-        Map<String, FormatValidator> formatValidators = new HashMap<>();
+        Map<String, AbstractFormatValidator> formatValidators = new HashMap<>();
 
         SpecificationVersion specVersion;
 
@@ -77,13 +77,13 @@ public SchemaLoaderBuilder() {
         }
 
         /**
-         * Registers a format validator with the name returned by {@link FormatValidator#formatName()}.
+         * Registers a format validator with the name returned by {@link AbstractFormatValidator#formatName()}.
          *
          * @param formatValidator
          *         the format validator to be registered with its name
          * @return {@code this}
          */
-        public SchemaLoaderBuilder addFormatValidator(FormatValidator formatValidator) {
+        public SchemaLoaderBuilder addFormatValidator(AbstractFormatValidator formatValidator) {
             formatValidators.put(formatValidator.formatName(), formatValidator);
             return this;
         }
@@ -99,7 +99,7 @@ public SchemaLoaderBuilder addFormatValidator(FormatValidator formatValidator) {
          */
         @Deprecated
         public SchemaLoaderBuilder addFormatValidator(String formatName,
-                final FormatValidator formatValidator) {
+                final AbstractFormatValidator formatValidator) {
             if (!Objects.equals(formatName, formatValidator.formatName())) {
                 formatValidators.put(formatName, new WrappingFormatValidator(formatName, formatValidator));
             } else {
@@ -206,7 +206,7 @@ public SchemaLoaderBuilder schemaJson(Object schema) {
             return this;
         }
 
-        SchemaLoaderBuilder formatValidators(Map<String, FormatValidator> formatValidators) {
+        SchemaLoaderBuilder formatValidators(Map<String,AbstractFormatValidator> formatValidators) {
             this.formatValidators = formatValidators;
             return this;
         }
@@ -448,7 +448,7 @@ SpecificationVersion specVersion() {
      * @deprecated
      */
     @Deprecated
-    Optional<FormatValidator> getFormatValidator(String formatName) {
+    Optional<AbstractFormatValidator> getFormatValidator(String formatName) {
         return Optional.ofNullable(config.formatValidators.get(formatName));
     }
 
diff --git a/core/src/main/java/org/everit/json/schema/loader/SpecificationVersion.java b/core/src/main/java/org/everit/json/schema/loader/SpecificationVersion.java
index b60403ad7..ef8bf45d8 100644
--- a/core/src/main/java/org/everit/json/schema/loader/SpecificationVersion.java
+++ b/core/src/main/java/org/everit/json/schema/loader/SpecificationVersion.java
@@ -10,6 +10,7 @@
 import java.util.List;
 import java.util.Map;
 
+import org.everit.json.schema.AbstractFormatValidator;
 import org.everit.json.schema.FormatValidator;
 import org.everit.json.schema.internal.DateFormatValidator;
 import org.everit.json.schema.internal.DateTimeFormatValidator;
@@ -48,7 +49,7 @@ enum SpecificationVersion {
             return "http://json-schema.org/draft-04/schema";
         }
 
-        @Override Map<String, FormatValidator> defaultFormatValidators() {
+        @Override Map<String, AbstractFormatValidator> defaultFormatValidators() {
             return V4_VALIDATORS;
         }
 
@@ -69,7 +70,7 @@ enum SpecificationVersion {
             return "http://json-schema.org/draft-06/schema";
         }
 
-        @Override Map<String, FormatValidator> defaultFormatValidators() {
+        @Override Map<String, AbstractFormatValidator> defaultFormatValidators() {
             return V6_VALIDATORS;
         }
 
@@ -90,7 +91,7 @@ enum SpecificationVersion {
             return "http://json-schema.org/draft-07/schema";
         }
 
-        @Override Map<String, FormatValidator> defaultFormatValidators() {
+        @Override Map<String, AbstractFormatValidator> defaultFormatValidators() {
             return V7_VALIDATORS;
         }
     };
@@ -129,7 +130,7 @@ private static List<String> keywords(String... keywords) {
         return unmodifiableList(asList(keywords));
     }
 
-    private static final Map<String, FormatValidator> V4_VALIDATORS = formatValidators(null,
+    private static final Map<String, AbstractFormatValidator> V4_VALIDATORS = formatValidators(null,
             new DateTimeFormatValidator(),
             new URIV4FormatValidator(),
             new EmailFormatValidator(),
@@ -138,14 +139,14 @@ private static List<String> keywords(String... keywords) {
             new HostnameFormatValidator()
     );
 
-    private static final Map<String, FormatValidator> V6_VALIDATORS = formatValidators(V4_VALIDATORS,
+    private static final Map<String, AbstractFormatValidator> V6_VALIDATORS = formatValidators(V4_VALIDATORS,
             new JsonPointerFormatValidator(),
             new URIFormatValidator(),
             new URIReferenceFormatValidator(),
             new URITemplateFormatValidator()
     );
 
-    private static final Map<String, FormatValidator> V7_VALIDATORS = formatValidators(V6_VALIDATORS,
+    private static final Map<String, AbstractFormatValidator> V7_VALIDATORS = formatValidators(V6_VALIDATORS,
             new DateFormatValidator(),
             new URIFormatValidator(false),
             new TimeFormatValidator(),
@@ -153,8 +154,8 @@ private static List<String> keywords(String... keywords) {
             new RelativeJsonPointerFormatValidator()
     );
 
-    private static Map<String, FormatValidator> formatValidators(Map<String, FormatValidator> parent, FormatValidator... validators) {
-        Map<String, FormatValidator> validatorMap = (parent == null) ? new HashMap<>() : new HashMap<>(parent);
+    private static Map<String, AbstractFormatValidator> formatValidators(Map<String, AbstractFormatValidator> parent, FormatValidator... validators) {
+        Map<String, AbstractFormatValidator> validatorMap = (parent == null) ? new HashMap<>() : new HashMap<>(parent);
         for (FormatValidator validator : validators) {
             validatorMap.put(validator.formatName(), validator);
         }
@@ -169,7 +170,7 @@ private static Map<String, FormatValidator> formatValidators(Map<String, FormatV
 
     abstract String metaSchemaUrl();
 
-    abstract Map<String, FormatValidator> defaultFormatValidators();
+    abstract Map<String, AbstractFormatValidator> defaultFormatValidators();
 
     public boolean isAtLeast(SpecificationVersion lowerInclusiveBound) {
         return this.ordinal() >= lowerInclusiveBound.ordinal();
diff --git a/core/src/main/java/org/everit/json/schema/loader/StringSchemaLoader.java b/core/src/main/java/org/everit/json/schema/loader/StringSchemaLoader.java
index 1633f9f3e..d9f6bb229 100644
--- a/core/src/main/java/org/everit/json/schema/loader/StringSchemaLoader.java
+++ b/core/src/main/java/org/everit/json/schema/loader/StringSchemaLoader.java
@@ -6,7 +6,7 @@
 
 import java.util.Map;
 
-import org.everit.json.schema.FormatValidator;
+import org.everit.json.schema.AbstractFormatValidator;
 import org.everit.json.schema.StringSchema;
 
 /**
@@ -16,7 +16,7 @@ public class StringSchemaLoader {
 
     private LoadingState ls;
 
-    private Map<String, FormatValidator> formatValidators;
+    private Map<String, AbstractFormatValidator> formatValidators;
 
     private boolean useDefault;
 
@@ -30,7 +30,7 @@ public StringSchemaLoader(LoadingState ls) {
         this(ls, DRAFT_4.defaultFormatValidators());
     }
 
-    StringSchemaLoader(LoadingState ls, Map<String, FormatValidator> formatValidators) {
+    StringSchemaLoader(LoadingState ls, Map<String, AbstractFormatValidator> formatValidators) {
         this.ls = requireNonNull(ls, "ls cannot be null");
         this.formatValidators = unmodifiableMap(requireNonNull(formatValidators, "formatValidators cannot be null"));
     }
@@ -48,7 +48,7 @@ public StringSchema.Builder load() {
     }
 
     private void addFormatValidator(StringSchema.Builder builder, String formatName) {
-        FormatValidator formatValidator = formatValidators.get(formatName);
+        AbstractFormatValidator formatValidator = formatValidators.get(formatName);
         if (formatValidator != null) {
             builder.formatValidator(formatValidator);
         }
diff --git a/core/src/main/java/org/everit/json/schema/loader/internal/WrappingFormatValidator.java b/core/src/main/java/org/everit/json/schema/loader/internal/WrappingFormatValidator.java
index 92e1460b9..35c501914 100644
--- a/core/src/main/java/org/everit/json/schema/loader/internal/WrappingFormatValidator.java
+++ b/core/src/main/java/org/everit/json/schema/loader/internal/WrappingFormatValidator.java
@@ -1,28 +1,33 @@
 package org.everit.json.schema.loader.internal;
 
-import org.everit.json.schema.FormatValidator;
+import org.everit.json.schema.AbstractFormatValidator;
 
+import java.util.Map;
 import java.util.Optional;
 
 import static java.util.Objects.requireNonNull;
 
-public class WrappingFormatValidator implements FormatValidator {
+public class WrappingFormatValidator implements AbstractFormatValidator {
 
     private final String formatName;
-    private final FormatValidator formatValidator;
+    private final AbstractFormatValidator formatValidator;
 
-    public WrappingFormatValidator(String formatName, FormatValidator wrappedValidator) {
+    public WrappingFormatValidator(String formatName, AbstractFormatValidator wrappedValidator) {
         this.formatName = requireNonNull(formatName, "formatName cannot be null");
         this.formatValidator = requireNonNull(wrappedValidator, "wrappedValidator cannot be null");
     }
 
 
-
     @Override
     public Optional<String> validate(String subject) {
         return formatValidator.validate(subject);
     }
 
+    @Override
+    public Optional<String> validate(String subject, Map<String, Object> unprocessedProperties) {
+        return formatValidator.validate(subject, unprocessedProperties);
+    }
+
     @Override
     public String formatName() {
         return formatName;
diff --git a/core/src/test/java/org/everit/json/schema/StringSchemaTest.java b/core/src/test/java/org/everit/json/schema/StringSchemaTest.java
index 9c70cb28a..13d815164 100644
--- a/core/src/test/java/org/everit/json/schema/StringSchemaTest.java
+++ b/core/src/test/java/org/everit/json/schema/StringSchemaTest.java
@@ -28,7 +28,7 @@ private static Schema loadWithNullableSupport(JSONObject rawSchemaJson) {
     @Test
     public void formatFailure() {
         StringSchema subject = buildWithLocation(StringSchema.builder()
-                .formatValidator(subj -> Optional.of("violation")));
+                .formatValidator(((FormatValidator)((subj) -> Optional.of("violation")))));
         TestSupport.failureOf(subject)
                 .expectedKeyword("format")
                 .input("string")
@@ -37,7 +37,7 @@ public void formatFailure() {
 
     @Test
     public void formatSuccess() {
-        StringSchema subject = StringSchema.builder().formatValidator(subj -> Optional.empty()).build();
+        StringSchema subject = StringSchema.builder().formatValidator(((FormatValidator)((subj) -> Optional.empty()))).build();
         subject.validate("string");
     }
 
diff --git a/core/src/test/java/org/everit/json/schema/internal/DefaultFormatValidatorTest.java b/core/src/test/java/org/everit/json/schema/internal/DefaultFormatValidatorTest.java
index f70aead47..c7c6e42a3 100644
--- a/core/src/test/java/org/everit/json/schema/internal/DefaultFormatValidatorTest.java
+++ b/core/src/test/java/org/everit/json/schema/internal/DefaultFormatValidatorTest.java
@@ -18,6 +18,7 @@
 import org.everit.json.schema.FormatValidator;
 import org.junit.Test;
 
+import java.util.Map;
 import java.util.Optional;
 
 import static org.everit.json.schema.internal.ValidatorTestSupport.assertFailure;
diff --git a/core/src/test/java/org/everit/json/schema/internal/URIV4FormatValidatorTest.java b/core/src/test/java/org/everit/json/schema/internal/URIV4FormatValidatorTest.java
index fdb455f9b..c7f512a53 100644
--- a/core/src/test/java/org/everit/json/schema/internal/URIV4FormatValidatorTest.java
+++ b/core/src/test/java/org/everit/json/schema/internal/URIV4FormatValidatorTest.java
@@ -9,16 +9,16 @@ public class URIV4FormatValidatorTest {
 
     @Test
     public void relativeURI() {
-        assertFalse(new URIV4FormatValidator().validate("abc").isPresent());
+        assertFalse(new URIV4FormatValidator().validate("abc",null).isPresent());
     }
 
     @Test
     public void absoluteURI() {
-        assertFalse(new URIV4FormatValidator().validate("http://a.b.c").isPresent());
+        assertFalse(new URIV4FormatValidator().validate("http://a.b.c",null).isPresent());
     }
 
     @Test
     public void notURI() {
-        assertTrue(new URIV4FormatValidator().validate("\\\\\\\\WINDOWS\\\\fileshare").isPresent());
+        assertTrue(new URIV4FormatValidator().validate("\\\\\\\\WINDOWS\\\\fileshare",null).isPresent());
     }
 }
diff --git a/core/src/test/java/org/everit/json/schema/internal/ValidatorTestSupport.java b/core/src/test/java/org/everit/json/schema/internal/ValidatorTestSupport.java
index d434b557e..0351d9928 100644
--- a/core/src/test/java/org/everit/json/schema/internal/ValidatorTestSupport.java
+++ b/core/src/test/java/org/everit/json/schema/internal/ValidatorTestSupport.java
@@ -2,6 +2,7 @@
 
 import static org.junit.Assert.assertTrue;
 
+import java.util.Map;
 import java.util.Optional;
 
 import org.everit.json.schema.FormatValidator;
@@ -10,13 +11,21 @@
 public final class ValidatorTestSupport {
 
     static void assertSuccess(String subject, FormatValidator format) {
-        Optional<String> opt = format.validate(subject);
+        assertSuccess(subject, format, null);
+    }
+
+    static void assertSuccess(String subject, FormatValidator format, Map<String, Object> unprocessedProperties) {
+        Optional<String> opt = format.validate(subject, unprocessedProperties);
         Assert.assertNotNull("the optional is not null", opt);
         Assert.assertFalse("failure not exist", opt.isPresent());
     }
 
     static void assertFailure(String subject, FormatValidator format, String expectedFailure) {
-        Optional<String> opt = format.validate(subject);
+        assertFailure(subject, format, null, expectedFailure);
+    }
+
+    static void assertFailure(String subject, FormatValidator format, Map<String, Object> unprocessedProperties, String expectedFailure) {
+        Optional<String> opt = format.validate(subject, unprocessedProperties);
         Assert.assertNotNull("the optional is not null", opt);
         assertTrue("failure exists", opt.isPresent());
         Assert.assertEquals(expectedFailure, opt.get());
diff --git a/core/src/test/java/org/everit/json/schema/loader/CustomFormatValidatorExtTest.java b/core/src/test/java/org/everit/json/schema/loader/CustomFormatValidatorExtTest.java
new file mode 100644
index 000000000..926469c50
--- /dev/null
+++ b/core/src/test/java/org/everit/json/schema/loader/CustomFormatValidatorExtTest.java
@@ -0,0 +1,123 @@
+/*
+ * Copyright (C) 2011 Everit Kft. (http://www.everit.org)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *         http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.everit.json.schema.loader;
+
+import org.everit.json.schema.ContextualFormatValidator;
+import org.everit.json.schema.ResourceLoader;
+import org.everit.json.schema.ValidationException;
+import org.json.JSONObject;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+
+import static org.junit.Assert.assertEquals;
+
+public class CustomFormatValidatorExtTest {
+
+    private final ResourceLoader loader = ResourceLoader.DEFAULT;
+
+    static class DivisibleValidator implements ContextualFormatValidator {
+
+        @Override
+        public Optional<String> validate(final String subject, final Map<String, Object> unprocessedProperties) {
+            if (unprocessedProperties.containsKey("factors")) {
+                try {
+                    long divisible = Long.parseLong(subject);
+                    try {
+                        List<String> factors = (List<String>) unprocessedProperties.get("factors");
+                        for (String strFactor: factors) {
+                            try {
+                                long factor = Long.parseLong(strFactor);
+                                if (divisible % factor != 0) {
+                                    return Optional.of(String.format("[%s] is not divisible by [%s]", subject, strFactor));
+                                }
+                            } catch(NumberFormatException nfe) {
+                                return Optional.of(String.format("the factor [%s] is not a parsable number", strFactor));
+                            }
+                        }
+                        return Optional.empty();
+                    } catch(ClassCastException cce) {
+                        return Optional.of("'factors' is not an array in JSON Schema");
+                    }
+                } catch(NumberFormatException nfe) {
+                    return Optional.of(String.format("the string [%s] is not a parsable number", subject));
+                }
+            } else {
+                return Optional.of(String.format("no declared 'factors' in JSON Schema", subject));
+            }
+        }
+
+        @Override
+        public String formatName() {
+            return "divisible";
+        }
+    }
+
+    @Test
+    public void testWorks() {
+        SchemaLoader schemaLoader = SchemaLoader.builder()
+                .schemaJson(baseSchemaJson())
+                .addFormatValidator("divisible", new DivisibleValidator())
+                .build();
+        
+        try {
+            schemaLoader.load().build().validate(loader.readObj("customformat-ext-works_data.json"));
+        } catch (ValidationException ve) {
+            Assert.fail("throwed exception");
+        }
+    }
+
+    @Test
+    public void testFail() {
+        SchemaLoader schemaLoader = SchemaLoader.builder()
+                .schemaJson(baseSchemaJson())
+                .addFormatValidator("divisible", new DivisibleValidator())
+                .build();
+        
+        try {
+            schemaLoader.load().build().validate(loader.readObj("customformat-ext-fail_data.json"));
+            Assert.fail("did not throw exception");
+        } catch (ValidationException ve) {
+        }
+    }
+
+    @Test
+    public void nameOverride() {
+        JSONObject rawSchemaJson = baseSchemaJson();
+        JSONObject idPropSchema = (JSONObject) rawSchemaJson.query("/properties/v");
+        idPropSchema.put("format", "somethingelse");
+        SchemaLoader schemaLoader = SchemaLoader.builder()
+                .schemaJson(rawSchemaJson)
+                .addFormatValidator("somethingelse", new DivisibleValidator())
+                .build();
+        Object actual = fetchFormatValueFromOutputJson(schemaLoader);
+        assertEquals("somethingelse", actual);
+    }
+
+    private Object fetchFormatValueFromOutputJson(SchemaLoader schemaLoader) {
+        return new JSONObject(schemaLoader.load().build().toString())
+                .query("/properties/v/format");
+    }
+
+    private JSONObject baseSchemaJson() {
+        return loader.readObj("customformat-ext-schema.json");
+    }
+
+}
diff --git a/core/src/test/java/org/everit/json/schema/loader/CustomFormatValidatorTest.java b/core/src/test/java/org/everit/json/schema/loader/CustomFormatValidatorTest.java
index 229debf1c..b1b70bcb9 100644
--- a/core/src/test/java/org/everit/json/schema/loader/CustomFormatValidatorTest.java
+++ b/core/src/test/java/org/everit/json/schema/loader/CustomFormatValidatorTest.java
@@ -22,6 +22,7 @@
 import org.junit.Assert;
 import org.junit.Test;
 
+import java.util.Map;
 import java.util.Optional;
 
 import static org.junit.Assert.assertEquals;
diff --git a/core/src/test/java/org/everit/json/schema/loader/SchemaLoaderTest.java b/core/src/test/java/org/everit/json/schema/loader/SchemaLoaderTest.java
index 0928ae389..b0e2892ab 100644
--- a/core/src/test/java/org/everit/json/schema/loader/SchemaLoaderTest.java
+++ b/core/src/test/java/org/everit/json/schema/loader/SchemaLoaderTest.java
@@ -33,6 +33,7 @@
 import org.everit.json.schema.EmptySchema;
 import org.everit.json.schema.EnumSchema;
 import org.everit.json.schema.FalseSchema;
+import org.everit.json.schema.FormatValidator;
 import org.everit.json.schema.NotSchema;
 import org.everit.json.schema.NullSchema;
 import org.everit.json.schema.NumberSchema;
@@ -97,7 +98,7 @@ public void builderUsesDefaultSchemaClient() {
     public void customFormat() {
         Schema subject = SchemaLoader.builder()
                 .schemaJson(get("customFormat"))
-                .addFormatValidator("custom", obj -> Optional.of("failure"))
+                .addFormatValidator("custom", ((FormatValidator)((obj) -> Optional.of("failure"))))
                 .build().load().build();
         TestSupport.expectFailure(subject, "asd");
     }
diff --git a/core/src/test/java/org/everit/json/schema/loader/SpecificationVersionTest.java b/core/src/test/java/org/everit/json/schema/loader/SpecificationVersionTest.java
index dd008fd03..4df725ab1 100644
--- a/core/src/test/java/org/everit/json/schema/loader/SpecificationVersionTest.java
+++ b/core/src/test/java/org/everit/json/schema/loader/SpecificationVersionTest.java
@@ -11,7 +11,7 @@
 import java.util.Map;
 import java.util.Set;
 
-import org.everit.json.schema.FormatValidator;
+import org.everit.json.schema.AbstractFormatValidator;
 import org.junit.Test;
 
 public class SpecificationVersionTest {
@@ -24,14 +24,14 @@ public void v6ContainsAdditionalFormats() {
 
     @Test
     public void v4MapMatchesFormatNames() {
-        for (Map.Entry<String, FormatValidator> entry : DRAFT_4.defaultFormatValidators().entrySet()) {
+        for (Map.Entry<String, AbstractFormatValidator> entry : DRAFT_4.defaultFormatValidators().entrySet()) {
             assertEquals(entry.getKey(), entry.getValue().formatName());
         }
     }
 
     @Test
     public void v6MapMatchesFormatNames() {
-        for (Map.Entry<String, FormatValidator> entry : DRAFT_6.defaultFormatValidators().entrySet()) {
+        for (Map.Entry<String, AbstractFormatValidator> entry : DRAFT_6.defaultFormatValidators().entrySet()) {
             assertEquals(entry.getKey(), entry.getValue().formatName());
         }
     }
diff --git a/core/src/test/resources/org/everit/jsonvalidator/customformat-ext-fail_data.json b/core/src/test/resources/org/everit/jsonvalidator/customformat-ext-fail_data.json
new file mode 100644
index 000000000..aef402027
--- /dev/null
+++ b/core/src/test/resources/org/everit/jsonvalidator/customformat-ext-fail_data.json
@@ -0,0 +1,3 @@
+{
+  "v": "21"
+}
diff --git a/core/src/test/resources/org/everit/jsonvalidator/customformat-ext-schema.json b/core/src/test/resources/org/everit/jsonvalidator/customformat-ext-schema.json
new file mode 100644
index 000000000..f070b7c44
--- /dev/null
+++ b/core/src/test/resources/org/everit/jsonvalidator/customformat-ext-schema.json
@@ -0,0 +1,14 @@
+{
+  "$schema": "http://json-schema.org/draft-04/schema#",
+  "type": "object",
+  "properties": {
+    "v": {
+      "type": "string",
+      "format": "divisible",
+      "factors": [ "3", "5" ]
+    }
+  },
+  "required": [
+    "v"
+  ]
+}
diff --git a/core/src/test/resources/org/everit/jsonvalidator/customformat-ext-works_data.json b/core/src/test/resources/org/everit/jsonvalidator/customformat-ext-works_data.json
new file mode 100644
index 000000000..5342cbb45
--- /dev/null
+++ b/core/src/test/resources/org/everit/jsonvalidator/customformat-ext-works_data.json
@@ -0,0 +1,3 @@
+{
+  "v": "15"
+}