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Create session metrics with an agent

The interesting question about a session is often one nobody wrote a metric for. An agent connected to the SignalFlag MCP server can take your previously evaluated field session data, propose a metric over it, show you the real chart, and save it once you approve.

Connecting

In Claude Code, install the Signal Flag plugin and add the MCP endpoint under the server name signal-flag:

Bash
claude plugin marketplace add resim-ai/signal-flag-plugin
claude plugin install signal-flag@signal-flag-plugins --scope user
claude mcp add --scope local --transport http signal-flag https://bff.resim.ai/mcp
claude --chrome

Authenticate with /mcp, connect Chrome with /chrome, and start the workflow:

Text
/signal-flag:explore-field-sessions

Local MCP configuration belongs to the directory you launch from, so run these where you intend to work.

How it works

  • It resolves what you mean. The agent confirms your organization and resolves the project, branch and session from a link, a list, or the page you have open in the web app.
  • It inspects real data. It reads the branch's topics and schemas, the existing metric definitions, and actual rows from the evaluation. When data is missing, it names what is absent and stops that proposal rather than guessing.
  • It asks about meaning. Units, clocks, frames, state values and how to treat gaps are agreed with you, not assumed.
  • It proposes new names. Each proposal uses a metric name not already used anywhere in the branch's metrics configuration, so existing definitions are never rewritten.
  • It shows the real chart. Where your MCP host renders charts, the agent draws one there. Otherwise it uses the Edit metric screen in your signed-in browser, which previews without saving. If neither is possible, it says so.

Approving and saving

Nothing is saved until you approve a specific definition for a specific evaluation. Changing either needs a fresh approval.

Once approved, the agent adds the metric to the evaluation you are looking at, where it appears on the Metrics tab. Other evaluations and existing metrics are unchanged. After saving, the agent reads the result back and reports what was stored.

Scope and limitations

  • Existing evaluations only. The agent adds metrics to evaluations that already exist. It does not register sessions, run evaluations, inspect local MCAP files or repositories, or author emissions or metrics builds.
  • New metrics only. Editing an existing metric is ordinary metric authoring. To draft metrics inside the web app, use Reeves.