Remit MCP Server

Remit

Know what an AI-written program can do before it runs.

Remit is a small, statically checked language for agent workflows, meaning programs that call tools and models. It is meant to be written and edited by AI agents. Before a program runs, the checker reports:

• which capabilities it can use, from a host-controlled list;
• at most how many times it can call each one, and its worst-case spend;
• whether untrusted data (documents, web pages, model output) or private data can reach sensitive parameters, such as payment details or email recipients. Each such flow is rejected outright, or sent to a human for approval bound to the exact arguments.

A runtime broker then enforces the same rules and records a replayable trace.

Try it in your browser: https://77-68-52-20.sslip.io/try.html (pick an edit an AI might make and see it allowed or blocked, with the reason). For AI agents: connect the MCP server at https://77-68-52-20.sslip.io/mcp.

payments.schedule(vendor_id: vendor.id, iban: inv.iban_on_invoice, amount: inv.amount, ...)

error[E0301]: data tagged untrusted flows into 'payments.schedule' parameter 'iban', which denies it
  note: 'inv.iban_on_invoice' is untrusted because it derives from inbox.read (line 20)

For AI agents

• MCP server, local: remit mcp (stdio).

• MCP server, hosted: remit mcp --http, with optional API keys and usage metering.

• Tools:

  Tool	What it does
  remit_guide	the guide or the full spec
  remit_check	errors plus the authority manifest
  remit_format	canonical formatting
  remit_authority_diff	did an edit widen authority?
  remit_examples	complete example programs
  remit_run_fixtures	offline test runs

• Quick guide: docs/AI_GUIDE.md.

• Full specification: docs/LANGUAGE_SPEC.md.

• llms.txt: site/llms.txt, plus site/llms-full.txt.

Claude Code configuration example:

{ "mcpServers": { "remit": { "command": "remit", "args": ["mcp"] } } }

Quick start

python3 -m venv .venv && .venv/bin/pip install -e ".[mcp]" pytest pydantic
.venv/bin/python -m pytest -q tests baselines
cd examples/invoices
../../.venv/bin/remit check invoices.rmt                                   # manifest and policy check
../../.venv/bin/remit run invoices.rmt                                     # offline fixtures; stops for approval
../../.venv/bin/remit approve <digest> && ../../.venv/bin/remit resume <run-id>   # approve that exact call, continue

Evidence

docs/BENCHMARKS.md compares Remit with a Python baseline that uses the same runtime, so runtime features are not credited to the language. Samples are small, use one model family and include no human trials.

• Safety:
  • Of 17 unsafe program mutations, 14 were rejected before running. Python on the same runtime executed 8 of them.
  • Asked to make unsafe changes, Haiku 4.5 agents shipped executable unsafe code 0/6 times in Remit and 6/6 in Python. Sonnet 5.5 refused in both languages.
• Review: every agent-written feature change (20 of 20) was mechanically shown not to widen authority.
• Ease:
  • Agents modified programs (15/15 against 14/15) and built a new workflow from a spec (5/5 against 5/5) equally well in both languages, so there is no penalty for a language the models had never seen.
  • Agents that only had the MCP server built correct programs 5/5.
• Recovery: crash-and-resume behaviour is identical in both, as expected, since it is a runtime property.

Status

Remit is an early, open-source release. The language, checker, runtime, MCP server, demo and five example apps all work and are tested. It is not yet a finished product: there is no built-in sandboxing (run it inside your own isolated environment) and no module system, concurrency or editor language server yet. See LANGUAGE_SPEC §13 for what is planned.

Running your own copy of the website and MCP server is covered in deploy/README.md.

Licence: Apache-2.0.