MCP server Agent Middleware

Agent Middleware

Agent Middleware is a gateway you put in front of an agent's risky tools (refunds, payouts, deploys) so each action needs a signed permit, runs at most once per request key, and leaves a signed receipt anyone can check offline.

Status: Pre revenue, pre release, solo maintained. There are no paying customers or production deployments to point to. We are looking for design partners with one real consequential tool. Install from source; nothing is published to PyPI or npm.

Try it in 3 minutes

Use the hosted demo. Get a demo key at the demo key page. The example also needs the associated wallet ID.

Connecting an MCP client to the hosted endpoint https://api.agentmiddleware.dev/mcp? Get an API key and send it as the X-API-Key header.

git clone https://github.com/agentmiddleware/amw-demo.git
cd amw-demo
python3 -m venv .venv
source .venv/bin/activate
pip install -e .
export AMW_API_KEY='<your key>'
export AMW_WALLET_ID='<your wallet id>'
python examples/permit_echo_retry.py

The example creates a permit, calls the reference echo tool, retries with the same key, and checks the receipt offline.

Run it locally

Use the gateway Makefile to start a local gateway. QUICKSTART.md has the full walk through.

git clone https://github.com/agentmiddleware/agent-middleware
cd agent-middleware/gateway
make quickstart

Concepts

• Permit: A signed grant that limits an agent to specified tools, a budget, and an expiry.
• Call: A governed MCP tool invocation under a permit.
• Request key: The Idempotency-Key header that identifies a request for retry handling.
• Receipt: A signed record of a call's outcome and hashes of its request and response, with a debit link when applicable.
• Credits: Internal metering units, not money.

Guarantees and limits

• a retry with the same key returns the original receipt instead of dispatching again
• a new key is a new request
• Reusing a key with a different request fails with a conflict before dispatch.
• A delivery_uncertain receipt means no trustworthy answer came back. The debit is kept, and the operator must reconcile with the downstream tool. The gateway does not resend automatically.
• The gateway limits dispatch and debit per key, but remote effects depend on the tool honoring the forwarded key. A receipt signs request and response hashes, not raw tool content, and cannot prove a remote effect happened. This is not exactly once.

Read Security Limitations before relying on the gateway for a consequential action.

Repo map

This repository holds the reference gateway, protocol spec, SDKs, integrations, and design-partner pilot loop (start with QUICKSTART.md). The separate agent-middleware-api repository is outside this checkout; partner evaluation guidance is here.

Apache 2.0 (gateway is Fair Source, FSL-1.1)