AIToday
AI Coding AssistantsZenn AI/MLPublished: Oct 4, 2026, 22:00 JST

GitHub, VS Code set rules for AI coding tasks

GitHub, VS Code set rules for AI coding tasks

3 Key Points

  1. What happened

    GitHub's material for its Copilot cloud agent urges developers to state the problem, completion conditions and files to change, while VS Code docs describe saving shared rules in Markdown instruction files.

  2. Why it matters

    The guidance treats a written completion condition as the yardstick for judging whether a request was carried out, so checking the result does not start from scratch after the code is written.

  3. What to watch

    It hinges on whether the instruction file is actually found and followed, since VS Code docs separate those two, and one example order is to read docs/PROJECT.md before changing anything.

WHO IT HITSTeams using AI coding assistants inside an existing repository feel this most: they need a short statement of scope and a written definition of done before the agent starts. The same shift lands on anyone who later reviews the generated changes and has to confirm rejected input left existing data untouched.

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Context & Analysis

The starting point of this piece is a habit many people fall into: asking an AI to "build the article management feature" and beginning there. That request alone leaves open what gets stored, what happens when the same ID arrives twice, and what counts as finished — and once the code exists, making those decisions from zero is painful. The article's answer is not to write a detailed spec up front, but to write down the scope of this one change and how the finished thing will be checked.

From there, the article draws on two official sources. GitHub's material for its Copilot cloud agent recommends making the problem to solve, the completion conditions, and hints about which files to change explicit. VS Code's documentation describes a mechanism for saving shared development policy in a Markdown instruction file, while noting that the supported format and the way it is read differ depending on the agent chosen. The article's example request shows what this looks like in practice — listing what to save, what to check first, and four things to verify when done, including that re-registering the same ID must not overwrite an existing article.

The remaining thread is verification. The article separates a file merely being found from instructions actually being followed, and suggests trying a representative task under the same conditions and comparing referenced information, generated files and results. It also warns that "tests passed" is not the same as the behavior you cared about being confirmed, and asks for a note on what was tried and what could not be tried. The wider context is that instruction files generated by AI should themselves be reread, since they may describe test procedures that do not exist yet or point at the wrong location. Whether this approach holds up likely depends on how much of the request is genuinely one-off and how much is a rule worth keeping in the repository.

FAQ
What should I write before asking an AI to implement a feature?
The guidance cited here says to make the problem you want solved, the completion conditions, and clues about which files to change explicit. A request example also lists what to save, what to check first, and what to verify once it is done.
Where should rules that apply every time go?
One-off requirements belong in the request, while rules used repeatedly are better kept in the repository. VS Code offers a mechanism for saving shared development policy in a Markdown instruction file, but the supported format and how it is read differ by the agent selected.
How do I check that my instructions were actually used?
Start with one small change. VS Code's official guide distinguishes the file being found from the instructions being followed on the job, and suggests running a representative task under the same conditions and comparing the referenced information, generated files and results.

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