Martin Fowler

In the past few weeks, multiple “autonomous background coding agents” have been released.

Supervised coding agents: Interactive chat agents that are driven and steered by a developer. Create code locally, in the IDE. Tool examples: GitHub Copilot, Windsurf, Cursor, Cline, Roo Code, Claude Code, Aider, Goose, … Autonomous background coding agents: Headless agents that you send off to work autonomously through a whole task. Code gets created in an environment spun up exclusively for that agent, and usually results in a pull request. Some of them also are runnable locally though. Tool examples: OpenAI Codex, Google Jules, Cursor background agents, Devin, …

I gave a task to OpenAI Codex and some other agents to see what I can learn. The following is a record of one particular Codex run, to help you look behind the scenes and draw your own conclusions, followed by some of my own observations.

The

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