cyberchef-mcp-server

An MCP (Model Context Protocol) server that exposes CyberChef's ~480 data operations — encoding/decoding, hashing, compression, encryption, data format conversion, and more — as tools an LLM agent can call directly, via CyberChef's Node.js API.

Tools

Typical flow for an agent: cyberchef_list_operations (find the op) → cyberchef_operation_help (confirm its arguments) → cyberchef_bake (run it).

Note: CyberChef's Magic operation (auto-detecting unknown encodings) is a flow-control operation, and the Node API explicitly rejects flow-control operations in bake() — so it can't be exposed as a tool here, only the browser UI supports it.

Related MCP server: CTF MCP Server

Setup

npm install
npm run setup
npm run build

npm run setup is required, not optional — see "Why npm run setup?" below.

Running standalone

npm start

The server communicates over stdio, per MCP convention — it isn't a long-running HTTP service and won't print anything on stdout itself.

Registering with an MCP client

Add an entry to your client's MCP server config, pointing at the built entry point, e.g. for Claude Code / Claude Desktop:

{
  "mcpServers": {
    "cyberchef": {
      "command": "node",
      "args": ["/absolute/path/to/mcp-cyberchef/dist/index.js"]
    }
  }
}

Development

npm run dev         # run src/index.ts directly with tsx, restarting on change
npm test            # run the unit tests (node:test via tsx)
npm run build       # type-check and compile to dist/
npm run smoke-test  # spawn the built server and drive it with a real MCP client

Why npm run setup?

cyberchef@11.2.0's own postinstall script (npx grunt exec:fixCryptoApiImports && ...) requires grunt/grunt-exec/grunt-webpack/etc., which only exist in cyberchef's own devDependencies — npm never installs those for a consumer, so that postinstall always crashes a fresh npm install. .npmrc sets ignore-scripts=true project-wide so install can complete at all (this also skips harmless postinstalls, like esbuild's and tesseract.js's funding message).

npm run setup replaces the one fixup that actually matters for us: fixCryptoApiImports appends .mjs extensions to node_modules/crypto-api's relative imports, which Node's strict ESM resolver requires but crypto-api's published source omits — without it, every hash operation throws ERR_MODULE_NOT_FOUND. It also runs esbuild's install step by hand, since that's needed for tsx (used by npm run dev/test) and would otherwise be skipped along with everything else.

Two more of cyberchef's dependencies are simply missing from its published package.json (yaml, used by JSONtoYAML; js-yaml, used by YAMLToJSON) — those are just declared as direct dependencies here instead. js-yaml is pinned to ^4 deliberately: v5 dropped the default export cyberchef's source imports.