diff --git a/README.md b/README.md
index 8f00ff4..4c30647 100644
--- a/README.md
+++ b/README.md
@@ -539,6 +539,9 @@ These are available from the `@hyperjump/json-schema/experimental` export.
 
     Define a vocabulary that maps keyword name to keyword URIs defined using
     `addKeyword`.
+* **hasVocabulary**: (dialectId: string) => boolean;
+
+    Determine whether the vocabulary is supported.
 * **getKeywordId**: (keywordName: string, dialectId: string) => string
 
     Get the identifier for a keyword by its name.
@@ -568,14 +571,17 @@ These are available from the `@hyperjump/json-schema/experimental` export.
 * **getDialectIds**
 
     This function retrieves the identifiers of all loaded JSON Schema dialects.
-* **getDialect**:  (dialectId: string) => Record<string, string>;
+* **getDialect**: (dialectId: string) => Record<string, string>;
+
+    This function retrieves all the keywords appropriate for a particular
+    dialect.
+* **hasDialect**: (dialectId: string) => boolean;
 
-    This function retrieves all the keywords appropriate for a particular dialect.
+    Determine whether the dialect is supported.
 * **Validation**: Keyword
 
     A Keyword object that represents a "validate" operation. You would use this
     for compiling and evaluating sub-schemas when defining a custom keyword.
-        
 * **getSchema**: (uri: string, browser?: Browser) => Promise\<Browser>
 
     Get a schema by it's URI taking the local schema registry into account.
diff --git a/lib/experimental.d.ts b/lib/experimental.d.ts
index cd5a328..001ef55 100644
--- a/lib/experimental.d.ts
+++ b/lib/experimental.d.ts
@@ -60,6 +60,7 @@ export const getKeyword: <A>(id: string) => Keyword<A>;
 export const getKeywordByName: <A>(keywordName: string, dialectId: string) => Keyword<A>;
 export const getKeywordId: (keywordName: string, dialectId: string) => string;
 export const defineVocabulary: (id: string, keywords: Record<string, string>) => void;
+export const hasVocabulary: (vocabularyId: string) => boolean;
 export const loadDialect: (dialectId: string, dialect: Record<string, boolean>, allowUnknownKeywords?: boolean) => void;
 export const unloadDialect: (dialectId: string) => void;
 export const hasDialect: (dialectId: string) => boolean;
diff --git a/lib/experimental.js b/lib/experimental.js
index bd59ded..7da17bd 100644
--- a/lib/experimental.js
+++ b/lib/experimental.js
@@ -1,7 +1,7 @@
 export { compile, interpret, BASIC } from "./core.js";
 export {
   addKeyword, getKeyword, getKeywordByName, getKeywordName, getKeywordId,
-  defineVocabulary,
+  defineVocabulary, hasVocabulary,
   loadDialect, unloadDialect, hasDialect, getDialectIds, getDialect
 } from "./keywords.js";
 export { getSchema, toSchema, canonicalUri, buildSchemaDocument } from "./schema.js";
diff --git a/lib/keywords.js b/lib/keywords.js
index 2027cd0..4dd5386 100644
--- a/lib/keywords.js
+++ b/lib/keywords.js
@@ -34,6 +34,8 @@ export const defineVocabulary = (id, keywords) => {
   _vocabularies[id] = keywords;
 };
 
+export const hasVocabulary = (vocabularyId) => vocabularyId in _vocabularies;
+
 const _dialects = {};
 const _allowUnknownKeywords = {};