Agents & API: MCP and A2A Endpoints

Simulacra is not just a website: the same small Rust server that serves

this tracker exposes every playground experiment to other machines — as an

MCP tool server, as an A2A agent, and as plain JSON. All endpoints are

public, unauthenticated, rate-limited only by politeness, and seeded, so

every result is reproducible.

MCP (Model Context Protocol)

POST /mcp speaks JSON-RPC 2.0 over stateless streamable HTTP. Six tools

are exposed: the four experiments — run_town, run_variance,

run_coevolution, run_gossip, each taking an optional integer seed —

plus list_stages and get_stage for the research documents. Point any

MCP client at the URL and it can run the playground itself.

Endpoint: https://simulation.lucanian.app/mcp
Initialize: send {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"you","version":"0"}}}
List tools: send {"jsonrpc":"2.0","id":2,"method":"tools/list"}
Call a tool: send {"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"run_gossip","arguments":{"seed":42}}}
With curl: curl -s https://simulation.lucanian.app/mcp -H 'content-type: application/json' -d '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"run_gossip","arguments":{"seed":42}}}'

The same experiments are also an A2A agent. Its card is published at

/.well-known/agent.json (mirrored at /a2a/agent.json); send it a

natural-language message/send at /a2a/ — "run gossip seed 7" — and it

replies with a completed Task whose artifacts carry both a human-readable

summary and the raw JSON result. tasks/get retrieves a task by id; tasks

persist across restarts in an append-only JSONL log.

Agent card: https://simulation.lucanian.app/.well-known/agent.json
Endpoint: https://simulation.lucanian.app/a2a/
With curl: curl -s https://simulation.lucanian.app/a2a/ -H 'content-type: application/json' -d '{"jsonrpc":"2.0","id":1,"method":"message/send","params":{"message":{"role":"user","parts":[{"type":"text","text":"run variance seed 42"}]}}}'

For anything that does not speak agent protocols:

Humans can drive the same four experiments in the browser:

The server is std-only Rust with a hand-rolled JSON layer — no

dependencies. crates/server/src/mcp.rs and crates/server/src/a2a.rs in

whole implementation.