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How to give Codex a guarded, authorized MCP catalog with MCP Slim Guard

Route Codex through Slim Guard in Native mode so it sees authorized tools with full schemas.

Short answer: In the reviewed checkout, run npm ci, then npm run build, then npm link; then Change into your project directory and run mcp-slim-guard init, then mcp-slim-guard validate; edit mcp-slim-guard.yml so the tools allow and deny patterns match what Codex should reach. All steps.

Who it is forA developer using Codex on a project with MCP servers who wants the normal tool catalog but with allow/deny checks and call validation in front of it.

The problemConnecting Codex straight to upstream MCP servers gives no single place to enforce allow/deny rules or check arguments before the upstream is contacted.

The outcomeCodex lists only authorized original tool names with full schemas, and calls are validated before any upstream server is invoked.

What you need first

  • A reviewed checkout of the lennney/mcp-slim-guard repository (0.1.1-alpha.2 is not yet published to npm)
  • npm to run ci, build, and link the package
  • A project directory that already has an MCP configuration
  • An upstream MCP server definition you are authorized to use

Steps

  1. In the reviewed checkout, run npm ci, then npm run build, then npm link.
  2. Change into your project directory and run mcp-slim-guard init, then mcp-slim-guard validate.
  3. Edit mcp-slim-guard.yml so the tools allow and deny patterns match what Codex should reach.
  4. Run mcp-slim-guard plan --host codex to review the host plan without changing host files.
  5. Run mcp-slim-guard verify --host codex, then mcp-slim-guard install --host codex --mode native.

Prompt for your agent

Use the lennney/mcp-slim-guard repo to set up Native mode for Codex in the project at <project-path>. Run the plan and verify commands from the README and report the planned host entry. Confirm that `mcp-slim-guard verify --host codex` reports a configured runtime before you apply the install.

Caveat. The package is an alpha source candidate that is not on npm yet, and the README advises reviewing authorization patterns before using it with privileged tools.

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Using the Deduped MCP, get the setup steps for lennney/mcp-slim-guard and "Give Codex a guarded, authorized MCP catalog"

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claude mcp add --transport http deduped https://dedupedai.com/mcp

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