Baseline before edits
Record the branch, existing uncommitted changes, and current test result so new failures can be separated from old ones.
Operator pathLesson 03
Use a Coding Agent on a Real Project
Use a coding agent to inspect, change, and verify a small project while keeping every modification reviewable and reversible.
- Time
- 45 minutes
- Level
- Beginner to intermediate
- Reviewed
- August 1, 2026
Lesson outcome
You will complete one scoped code change with a baseline, an explicit plan, a readable diff, and verification evidence.
Before you start
- A Git repository or disposable practice project
- A coding agent such as Codex, Claude Code, Cursor, or Copilot
Mental model
Three ideas to keep
Scope is a safety tool
Name the files and behavior in scope. Tell the agent to preserve unrelated changes and ask before expanding the task.
Evidence closes the loop
A code change is not complete when the files look plausible. It is complete when the relevant build, tests, and user flow are verified.
Follow along
Complete the workflow
- 01
Capture the baseline
Run the repository's status command and its smallest relevant test. Save the output before asking for edits.
Expected result: You know which changes and failures already existed. - 02
Write a bounded request
Describe the intended behavior, files or area in scope, acceptance criteria, and actions that require approval.
Expected result: The request can be checked without guessing what 'better' means. - 03
Ask for inspection and a plan
Let the agent read the relevant code and explain the change path before editing. Correct the plan if it touches unrelated systems.
Expected result: The plan names the affected route, component, data source, and verification step. - 04
Review the diff
Inspect the changed files. Look for deleted behavior, broad refactors, new dependencies, secrets, and unrelated formatting churn.
Expected result: Every changed line can be connected to the requested behavior. - 05
Verify the story
Run the focused test, production build, and the actual browser flow when UI behavior changed.
Expected result: You have test output and a visible result, not only the agent's summary.
Practice task
Make one reversible UI improvement
Ask the coding agent to add a small empty-state message, improve one label, or fix one responsive spacing issue in a practice project.
You are done when:
- The initial Git state was recorded.
- Only expected files changed.
- The build passes and the page was checked at desktop and mobile widths.
Guardrails
Keep the exercise safe and reviewable
- Do not let an agent discard pre-existing uncommitted work.
- Do not paste production secrets into prompts or test fixtures.
- Require explicit approval for deployments, database writes, and destructive Git operations.