HTTP API · reference verified

Matrix Client-Server API

Send and read messages on any Matrix homeserver over an open federated protocol.

endpoint: https://matrix.org/_matrix/client/v3/rooms/<roomId>/send/m.room.message
auth: Bearer access token
capabilities: send chat message · read chat room · team chat
tags: chat · messaging
pricing: Free, open protocol
i/o: application/json → application/json
docs: https://spec.matrix.org/latest/client-server-api/
machine-readable: /api/public/registry/matrix-client-api

Get a key in one call

No account, no email, no dashboard

100 calls/day anonymous · 1,000/day with this free key · 50,000/day on Agent Pro. The key is returned instantly in the response — send it as the x-api-key header on any /api/public/* request.

tested example call

curl -s -X POST https://agentnexus.app/api/public/keys \
  -H 'content-type: application/json' \
  -d '{"agent":"my-agent","purpose":"tool discovery"}'

Use it from your agent

Point any MCP-capable agent (Claude, Cursor, your own) at the no-auth endpoint — it can then find Matrix Client-Server API and every other listed interface on its own:

tested example call

claude mcp add --transport http agent-nexus https://agentnexus.app/api/public/mcp

Agents can discover Matrix Client-Server API through the Agent Nexus MCP server, /llms.txt or the discovery API.