Fonoster
by fonoster
Fonoster's MCP server lets an agent look up phone numbers and voice apps in your self-hosted telephony stack, then place a single call or a batch of calls.
Add to Claude Code
claude mcp add fonoster -- npx -y @fonoster/mcp
Source: https://github.com/fonoster/fonoster/tree/main/mods/mcp
About
Fonoster is an open-source, self-hostable alternative to Twilio for programmable voice, and its MCP server (@fonoster/mcp) exposes that stack to AI agents: an agent can list the phone numbers and voice applications provisioned in a workspace, then place a call or a batch of calls against them.
The server ships as an npx-installable package that plugs into Claude Desktop or any MCP client, authenticating with a Fonoster workspace access key plus an API key/secret pair, and it includes a guided create_call_prompt that walks a user through picking a number and an application before dialing.
Key features
- Lists phone numbers and voice applications provisioned in a Fonoster workspace
- Places a single call or a batch of calls to multiple destinations in one request
- Guided create_call_prompt walks the caller-selection flow step by step
- Authenticates via workspace access key plus API key/secret, matching Fonoster's own auth model
- Runs anywhere Node/npx does, no extra telephony infrastructure beyond your Fonoster workspace
Use cases
- Triggering outbound notification or reminder calls through voice applications already built in Fonoster
- Looking up which numbers and applications exist in a workspace before wiring up a new campaign
- Kicking off batch outbound-calling runs, like appointment reminders, from a chat interface
- Prototyping voice-agent workflows without leaving an MCP client
Available tools
list_numbers
Returns the phone numbers available in a Fonoster workspace in table format, with optional pagination.
list_applications
Lists Fonoster voice applications, including their endpoints and creation dates.
create_call
Places a single outbound call given a from/to number pair, an application reference, and optional metadata.
create_call_batch
Places multiple outbound calls at once from an array of destination numbers.
Frequently asked questions
Do I need a Twilio-style paid account?
No. Fonoster is self-hosted and open source, so the MCP server talks to whichever Fonoster workspace you run, authenticated with a workspace access key and an API key/secret rather than a third-party billing account.
Can it dial more than one number at once?
Yes. create_call_batch accepts an array of destinations and places all of them in one request, alongside create_call for a single outbound call.