Graham Knapp

Testing GitHub Copilot agent mode

written by Graham Knapp on 2025-08-23

I tested GitHub Copilot agent mode in July 2025, setting Copilot to work online on different sized features - the workflow looks like this:

1. Chat with Copilot online - ask it to open a PR to work on a specific feature. Copilot starts working in its own virtual machine on GitHub.
2. 30 minutes later I get an email saying the PR is ready for review - I read it online and ask for any corrections via github.com
3. If and when I am happy with it I pull the branch to my PC, review, modify, fix, change.
4. I push from my machine and merge to trunk

Some stats:

• 19 Pull requests opened against our main monorepo in 5 weeks.
• 7 merged
• 8 still open on the 31st of July (3 of those created on the final day)
• 3 closed unmerged because they clearly didn't work or were not worth finishing
• 1 closed because I reimplemented it more successfully on my dev PC

For example, I tasked Copilot with refactoring 3 instances of near-duplicate code into a common service and make some improvements to error handling on the refactored service. My experience of code review from the last 4 years definitely helps with this workflow - reviewing code from an agent is similar to reviewing colleagues' code except that I don't feel guilty about leaving a PR unread for more than a day. Those PRs still become stale however and merge conflicts are a pain if the agent changes overlap with other PRs.

One challenge is that this makes it very easy to set Copilot working on easy to define low-impact work but that work still takes to review. It would be easy to get into the habit of doing lots of unimportant busy work with this workflow. I now want to explore how to use coding agents to achieve more ambitious changes, perhaps changes I would not take on individually because they lie near the limits of my current knowledge.

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