Dictionary MCP: definitions, synonyms, antonyms, and vocabulary discovery

Dictionary MCP gives AI agents and MCP-compatible applications structured English dictionary data on demand. Use it to clarify unfamiliar words, improve drafts, find alternatives, check opposites, or introduce a curated vocabulary word without maintaining a dictionary database or API key.

What you can do

• Give a writing assistant definitions, usage examples, pronunciation text, and available audio.
• Find deduplicated synonyms for rewriting, SEO copy, or brainstorming.
• Find antonyms for contrast, language learning, and vocabulary exercises.
• Request a randomly selected word from a curated 40-word list for prompts or daily learning.

MCP tools

All arguments are validated before the handler runs.

Tool	Arguments	Result
define-word	word — required non-empty string	JSON text with word, phonetic, and meanings. Every meaning contains partOfSpeech, definition objects (definition, nullable example, synonyms, antonyms), plus meaning-level synonym and antonym arrays. audioUrl is included when the upstream response provides one. The first dictionary entry is returned.
get-synonyms	word — required non-empty string	JSON text: { "word", "synonyms", "count" }. Terms are collected across all returned entries and meanings, deduplicated, and sorted alphabetically.
get-antonyms	word — required non-empty string	JSON text: { "word", "antonyms", "count" }, using the same deduplication and sorting behavior.
word-of-the-day	No arguments	JSON text with a randomly chosen curated word and, when available, phonetic, partOfSpeech, definition, nullable example, and audioUrl.

Tool results are returned as MCP text content. The text is JSON for successful structured lookups except define-word not-found responses, which are plain text.

Connect from an MCP client

Use the Apify Streamable HTTP endpoint:

https://reverberant-equality--dictionary-mcp.apify.actor/mcp

Send MCP requests with POST and authenticate with your Apify API token:

Authorization: Bearer <APIFY_API_TOKEN>
Content-Type: application/json
Accept: application/json, text/event-stream

Configure those values in any client that supports the MCP Streamable HTTP transport. The endpoint is not a conventional REST route: use MCP JSON-RPC methods and complete the normal MCP initialization sequence. GET /mcp and DELETE /mcp return method-not-allowed responses.

After initialization, a tool call payload looks like this:

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "define-word",
    "arguments": {
      "word": "serendipity"
    }
  }
}

The response’s result.content[0].text contains the definition data. MCP SDKs normally parse the JSON-RPC envelope for you.

Pricing and data source

The live price is $0.005 per tool call. Each handler emits one tool-call pay-per-event charge before it contacts the upstream service. A not-found word, an empty synonym list, or an upstream failure after charging can therefore still consume one paid call. Apify platform usage is billed separately according to the user’s Apify plan.

Definitions come from the public Free Dictionary API endpoint https://api.dictionaryapi.dev/api/v2/entries/en/{word}. The upstream service requires no API key. Pronunciations, examples, synonym coverage, antonym coverage, and audio availability depend entirely on its records.

Limitations and error behavior

• This server looks up English entries only. It does not translate, spell-check, conjugate, or search by definition.
• A valid word may have no examples, synonyms, antonyms, phonetic text, or audio. Missing collections are returned empty; nullable examples remain null; audioUrl is omitted when unavailable.
• A 404 from the upstream API becomes No definition found for "…". for define-word, or an empty array and count of zero for synonym and antonym tools.
• Unexpected network and upstream errors are logged and propagated as MCP errors. There is no cached fallback for ordinary lookups.
• word-of-the-day is random per invocation, not tied to a calendar date. If its API lookup fails, the tool still returns the selected word with note: "Definition unavailable from API.".
• The public upstream service may change, throttle, or be temporarily unavailable; no service-level guarantee is implied.

Privacy

The server does not write tool results to an Actor dataset, key-value store, or application database. Lookup words are processed in memory, forwarded to dictionaryapi.dev, and included in application logs for operational diagnostics. Apify and the upstream provider also receive normal request metadata under their own policies. Do not use lookup text for secrets or sensitive personal information. Your Bearer token is used by Apify to authorize the endpoint and should be stored in your MCP client’s secret configuration.

Local development

Node.js 20 or newer is required.

npm install
npm run start:dev       # http://localhost:3000/mcp
npm test                # Vitest suite
npm run build           # compile TypeScript to dist/
npm run start:prod      # run dist/main.js
apify validate-schema   # validate Actor configuration/schema

Set APIFY_CONTAINER_PORT to override port 3000. Local execution can log that pay-per-event charging was ignored when no Apify PPE environment is active; that is expected and does not remove charging in a monetized Actor run.