This tutorial explores using Codex, a coding agent, with GitLab for software development. It starts with fixing a WebSocket bug locally using Codex, then integrates GitLab MCP to incorporate issue requirements. Codex is used to fix the WebSocket bug, updating logic, adding tests, and creating a branch. It then leverages GitLab's CI/CD pipeline and code review. The second use case has Codex leverage GitLab MCP, integrating issue details directly before code changes. This enabled it to create a merge request and close the associated issue via MCP. The focus shifts to fixing a REST API validation bug, where Codex, as an external agent, addresses review feedback within a merge request. Codex adds documentation, tests, and commits fixes, all within the merge request context. This increases efficiency with code reviews and revision updates. Specific tips are provided for effective use of Codex and GitLab together, like a file named "AGENTS.md."