# How to Record MCP Tool Calls | Reelier

Place Reelier's recorder between the agent and a stdio MCP server. Calls that traverse that proxy are recorded. Supported command configuration can be rewritten, but plugin-owned manifests and URL entries are not rewritten, so those calls remain outside unless the plugin author wraps its stdio entry or the host exposes supported configuration.

Evidence state: traced against released `reelier@0.32.0` on 2026-08-12.

## Evidence note

The pinned initialization, wrapper, and recorder implementations trace how supported command entries are wrapped and how traversing MCP calls are recorded.

## Proxy placement

The wrapper fronts a stdio server command. The agent talks to the proxy and the proxy talks to the server, giving the recorder visibility into calls that traverse that process boundary.

## Supported configuration

Installation can rewrite supported command-based MCP configuration and retain a backup. URL entries are skipped because the wrapper itself speaks stdio.

## Calls the trace does not cover

Plugin-owned manifests load outside the supported host configuration unless the plugin author declares a wrapped stdio entry. Direct HTTP, native shell actions, and file edits outside the proxy are not captured by this path.

## Non-claims

This does not prove that an action was safe or semantically correct.

This does not prove that every write was observed or receipted.


## Falsifier

A call that traverses the configured stdio proxy but is absent from the resulting trace would falsify this claim.

## Sources

- [Pinned configuration discovery](https://github.com/seldonframe/reelier/blob/bd44bf81bbd41915543fb647f433ddb386cc6a1d/src/init.ts)
- [Pinned stdio wrapper](https://github.com/seldonframe/reelier/blob/bd44bf81bbd41915543fb647f433ddb386cc6a1d/src/wrap.ts)
- [Pinned recorder implementation](https://github.com/seldonframe/reelier/blob/bd44bf81bbd41915543fb647f433ddb386cc6a1d/src/recorder.ts)

## Citation-friendly definition

Reelier records MCP calls that traverse its stdio proxy; traffic outside that configured proxy is outside the trace's observation boundary.

## Related evidence

- [What an agent receipt actually proves](https://www.reelier.com/evidence/what-agent-receipt-proves)
- [MCP recording reference](https://www.reelier.com/learn/mcp-recording)

Canonical: https://www.reelier.com/evidence/record-mcp-tool-calls

Markdown twin: https://www.reelier.com/evidence/record-mcp-tool-calls/md