Skip to content
Agentic Levels

Everything starts here.

GuestLocal progress only
PreferencesSign in
01Start with one taskBest first move for beginners.02Check your LevelMeasure where you are.03Score an AI resultFind the habit to practice first.04Return to Your WorkScores, links, and checkpoints.
Start here

Begin

HomeThe main entry point.New to AIStart with one useful task.
Know where you are

Measure

Check your LevelUse this after you have tried AI.Fluency ScoreScore an AI result you can review.
Build the habit

Learn

LevelsLessonsTracks
Find the reference

Library

PromptsReferenceResourcesCompare Tools
Turn it into work

Apply

Your Next MoveChoose what AI should change next.Tool SetupGet the tools ready.
Come back later

Return

Your WorkScores, links, and checkpoints.My PathContinue from your level.Updates
Site

Site

PricingAboutFAQ & FeedbackPreferences

© 2026 Fuentes Studio

Privacy·Terms
yourCouncil
Ready to help
✦

What do you want to understand?

Ask anything about what you're learning.

Tracks›Codex Fundamentals
L6Lesson 1Free

Use MCP only for a real gap

More tools only help when they close a task boundary

After this, you'll be able to name the gap an MCP server closes for Codex and reject MCP setup when the repo already has enough context.

Before you start

Complete Use computer use for GUI work first.

The idea

MCP is not a badge. It is a way to give Codex context or tools it does not already have. Codex already reads the repo, runs commands, and uses configured surfaces. Add MCP only when the task crosses a boundary Codex cannot cross safely otherwise.

An MCP server is added before the task proves a missing capability.
An MCP server is added before the task proves a missing capability.
Gap TestMove through Use MCP only for a real gap, check proof, then fix only the weak part.
yesnorun it again
StartBegin with the real task
Use MCP only for a real gapAfter this, you'll be able to name the gap an MCP server closes for Codex and reject
1Proof visible?The answer names the context or action gap
Ready to useRun the MCP gap test for one Codex task and decide add or skip
Fix the weak partBreaks when MCP expands access without adding useful task context

Here is the before and after: before, Codex is guessing from a loose request. After, you can name the gap an MCP server closes for Codex and reject MCP setup when the repo already has enough context.

Now try it use the exercise prompt on one real repo task. Keep the output small enough to check before you accept the change.

You are ready when the Codex action, boundary, and proof all match the task.

Try it (12 min)

Watch out for

  • Installing MCP before defining the missing capability.
  • Giving Codex write-capable tools when read-only proof would be enough.
  • Duplicating file access Codex already has.
  • Ignoring tool output injection because the tool feels trusted.

Paste this into Claude

Run the MCP gap test:

Task: [describe task]
What Codex can already see: [repo, tests, browser, files, docs]
External context or action needed: [Figma, browser, docs, database, app, none]
Candidate MCP server: [name, or unknown]
Approval risk: [read-only, write, destructive, unknown]

Return:
1. Add MCP or skip MCP.
2. The exact gap it closes.
3. The approval or proof needed after adding it.
4. A simpler fallback if MCP is not ready.

Created by potrace 1.16, written by Peter Selinger 2001-2019 What a good response looks like

Add browser MCP only if the route requires signed-in state and the in-app browser cannot access it. Gap: Codex needs to verify a user-only flow. Risk: browser can act in an authenticated session, so approve actions narrowly and capture screenshots.

Created by potrace 1.16, written by Peter Selinger 2001-2019 What good looks like

  • The answer names the context or action gap
  • MCP is skipped when Codex already has enough access
  • Approval risk is named
  • A fallback exists

When this breaks

  • Breaks when MCP expands access without adding useful task context.
  • Breaks when tool responses are trusted without review and introduce hostile instructions.

AI can help with this

Use Codex to help you you can name the gap an MCP server closes for Codex and reject MCP setup when the repo already has enough context. Start with the exercise prompt and your real input. Ask for one draft, then check it against this proof: The answer names the context or action gap. Accept only the version you can verify yourself.

The task passes a gap test, picks one MCP, and checks the first tool call at the golden dot.

Created by potrace 1.16, written by Peter Selinger 2001-2019 You can now

✓

You can name the gap MCP closes

  • ✓You can skip MCP when it adds no value
  • ✓You can classify MCP approval risk
  • ✓You can choose a fallback

Key takeaways

Add MCP for a real boundary Codex cannot cross. More tools without a gap create more risk, not better work.

  1. 1MCP connects Codex to outside tools and context.
  2. 2Codex supports MCP in CLI and IDE extension.
  3. 3A useful MCP server closes a named gap.
  4. 4Tool responses still need trust checks.

Created by potrace 1.16, written by Peter Selinger 2001-2019 Go deeper

  • Codex MCP
  • Wire Your First MCP
  • Trust No Tool Response

Was this helpful?

Up nextAdd skills and plugins without bloat→

Related lessons

Wire Your First MCPRead a Tool Schema Like the Model DoesTrust No Tool Response
← Back to Codex Fundamentals