Deploy and Host midwire on Railway

midwire sits between your agent and an MCP server, and checks that writes actually landed. It reads back every write, catches writes that were dropped behind a 200, catches the same write sent twice, and records everything your agent did.

About Hosting midwire

You point midwire at an MCP server you already use. It registers that server's tools as its own and forwards every call, so your agent changes one URL and nothing else. After a write returns, midwire fires the read that confirms it and compares the two. Findings ride back to the agent in the tool result's metadata, and a status page shows what the agent did and what read back wrong.

Hosting it means one container, one volume for the ledger, and one environment variable. Every check is deterministic, so there is no GPU, no model and no inference cost.

Why Deploy midwire?

An agent calls a tool, reads its own report of what the call did, and moves on. The component that acts is the component that reports, so a write that silently fails is invisible. Practitioners describe the same failure repeatedly: the workflow logs a record creation that never hit the database.

midwire measures what actually changed and feeds that back before the agent continues. It annotates by default rather than blocking, because false positives are what get this kind of tool uninstalled. Tools that move money can opt into blocking.

It fails open. If a probe endpoint is down, traffic passes and the failure is counted, because a verifier that breaks your agent is worse than the bug it prevents.

Common Use Cases

Confirm that an agent's database writes, ticket updates or emails actually landed, instead of trusting the tool's status code
Catch duplicate non-idempotent writes before they create two records or two charges
Keep an audit trail of every tool call an agent made, with the findings attached

Dependencies for midwire

An MCP server for midwire to wrap, reachable over HTTP
A volume mounted at /data for the ledger

Deployment Dependencies

Set MIDWIRE_UPSTREAM_URL to the MCP server you want wrapped. Everything else has a default: the ledger and duplicate detection work with no further configuration, and read-back probes switch on when you declare write-to-read tool pairs in MIDWIRE_PROBES.