wixzel-phone-mcp

Wixzel Phone for AI agents. A Model Context Protocol server that lets Claude Code, Claude Desktop, Cursor, and any other MCP client create voice agents, connect a carrier, place calls, run campaigns, and read what it all cost, using the Wixzel Phone API.

Wixzel Phone: APIs for AI voice agents. One API key, one balance, every voice engine.

One tool per API operation, 56 in all, each annotated so a client knows which are read-only, which delete, and which spend money or make a real phone ring. Three prompts (quickstart, diagnose_call, spend_report) package the common workflows.

Install

You need a Wixzel Phone API key: Dashboard → API keys → Create key at phone.wixzel.com. Grant only the scopes the agent should have. Leave out billing:write unless you want it to be able to start top-ups.

Claude Code

claude mcp add wixzel-phone -e WIXZEL_API_KEY=wv_live_... -- npx -y wixzel-phone-mcp

Or commit a .mcp.json to the project so every collaborator gets it:

{
  "mcpServers": {
    "wixzel-phone": {
      "command": "npx",
      "args": ["-y", "wixzel-phone-mcp"],
      "env": { "WIXZEL_API_KEY": "${WIXZEL_API_KEY}" }
    }
  }
}

Then, in Claude Code:

/mcp__wixzel-phone__quickstart

Claude Desktop

Add to claude_desktop_config.json (Settings → Developer → Edit Config):

{
  "mcpServers": {
    "wixzel-phone": {
      "command": "npx",
      "args": ["-y", "wixzel-phone-mcp"],
      "env": { "WIXZEL_API_KEY": "wv_live_..." }
    }
  }
}

Cursor, Windsurf, VS Code, others

Same shape: command npx, args ["-y", "wixzel-phone-mcp"], env WIXZEL_API_KEY. Any client that speaks MCP over stdio works.

Remote (Streamable HTTP)

For clients that connect over HTTP, or to host one server for a team:

npx wixzel-phone-mcp --http 3939

The server listens on http://localhost:3939/mcp. Each request carries the caller's own key as Authorization: Bearer wv_live_...; the server is stateless and never mixes keys between requests. Set WIXZEL_API_KEY to provide a fallback key for requests that send none. GET /healthz reports liveness.

Related MCP server: Vapi MCP Server

What the agent can do

Prompts: quickstart (connect a carrier, register a number, build an agent, place a first call), diagnose_call (why did call X fail), spend_report (what did this month cost, and where).

Resources: wixzel://guide (the operating guide the server also sends as its instructions) and wixzel://connection (base URL and whether the key is live or test; never the key itself).

How it keeps the agent honest

• Money is explicit. place_call, start_campaign and create_topup are annotated openWorldHint: true and their descriptions tell the model to confirm with the user first. Clients that gate on annotations will ask before running them.

• Idempotency is automatic. The two money paths require an Idempotency-Key; the server generates one per call and accepts an explicit idempotency_key for deliberate retries, so a network timeout never turns into two calls.

• Errors are actionable. Every failure returns the API's machine-readable code, the request_id, and a hint that says what to do: which scope is missing, that the balance is short, that a cursor was mangled.

• Rate limits are absorbed. A 429 is retried after Retry-After up to twice before the model sees it. Those requests are never charged.

• Scopes do the gating. The key decides what works. There is no admin scope, and a key cannot create one broader than itself.

• Secrets stay put. SIP passwords are write-only; API key secrets appear once, in the tool result, and nowhere else. The key this server runs with is never exposed through any tool or resource.

Configuration

Development

npm install
npm test          # offline: a fake API behind an in-memory MCP client
npm run build     # dist/
npm run inspect   # opens the MCP Inspector against the built server

Run the built server against a real key:

WIXZEL_API_KEY=wv_test_... node dist/index.js

Tool schemas are hand-written zod, derived from the API's OpenAPI spec at docs/openapi.json in the wixzel-voice repository. When an endpoint is added there, add a tool in src/tools/.

License

MIT. Wixzel Phone itself is a hosted service; see phone.wixzel.com for terms.