What Codex + MCP Actually Do
Outcome
By the end of this lesson, you should be able to explain this in one sentence:
Codex handles reasoning and edits; MCP gives Codex safe, structured capabilities.
Mental Model
- You ask Codex for work.
- Codex decides whether it can do the work directly.
- If it needs a capability, it calls an MCP tool.
- The MCP server returns structured output.
- Codex continues with better context.
Why Build Your Own MCP
Build an MCP when you repeat the same workflow and want Codex to do it consistently.
Examples:
- Validate all route files with your project rules.
- Pull project-specific status from an internal API.
- Run a custom analysis pipeline with one tool call.
Course Goal
You will build one local MCP server and connect it to Codex.
At the end of this course, you should be able to:
- add a new tool in minutes,
- debug MCP failures quickly,
- and package your server for re-use.
Next
Continue to Scaffold an MCP Server.