---
name: mcp-setup
description: Use when installing, configuring, debugging, or verifying an MCP server for a harness, or when a configured server's tools are missing or failing.
when_to_use: "Trigger phrases: MCP tools missing, server not showing up, /mcp shows disconnected, re-authenticate the MCP, add an MCP server, tools still unavailable after login, mcp authorized but calls fail."
metadata:
  short-description: Install, repair, or verify an MCP server for a harness
---

# MCP Setup

Resolve the exact scope first: which harness, which configuration file, and
whether the server is global, project, or repository-local. Keep one
registration channel per server; duplicate registrations across scopes produce
conflicting tool lists and ambiguous failures.

Servers register at session start. Some harnesses reconnect a server or
refresh its tools live; after a configuration change, reconnect the server from
the harness's server menu when it offers one, otherwise restart the session. A
tool missing from a live session is not evidence of a broken server.

Treat diagnostic output as sensitive. A harness's server-list command and
configuration dumps can print arguments, headers, and connection strings
verbatim; filter values out before the output reaches the transcript. Start
with a read-only status check of the configured servers before any login
attempt. Match the authentication flow to the execution mode. Browser OAuth
needs an interactive terminal, not a local browser: on a remote or display-less
host, a login command that prints the authorization URL and accepts the pasted
callback URL completes the grant. A non-interactive session cannot finish it.
Complete the grant interactively beforehand, use sign-in stored outside the
repository, or route through a proxy command that owns its own authentication.
Record where the sign-in lives, and never write it into configuration
committed to a repository.

Attempt re-authentication at most once per server. If it fails, stop: report
the exact error text and the user action needed (complete the browser grant,
grant the missing scope, or fix the registration). Do not retry,
probe other login commands, or substitute a CLI for the server unless asked.
When a server needs login again the same day, find why before asking: a
provider with short-lived sign-ins and rejected refresh keeps expiring. Propose
a durable sign-in; ask to reconnect once per root cause.

Verify with a fresh probe, not the current session: start a new
non-interactive session, list the server's tools, and call one read-only tool.
Redact sign-in values and account identifiers before quoting probe output. A sandboxed
probe can report a healthy server as broken when the sandbox blocks its state
or socket files; re-run the probe outside the sandbox before concluding
failure.

On failure, report the harness, scope, configuration path, server name,
transport, authentication mode, exit status, and raw error. Use
`systematic-debugging` to distinguish launcher, authentication, quota, and
provider failures. Do not edit sign-in settings you cannot verify.