When you open an unfamiliar repository, a file list tells you what exists. It does not tell you what to read for the change you need to make, which assumptions matter, or where your understanding ends.
Use this guide as a sequence of investigations, not a promise to understand every codebase within a fixed number of days. Repository size, language, documentation, domain knowledge and access to teammates all affect the work.
In this article:
1. Start with a question, not the entire repository
Choose a question connected to real work: “Where is access to customer accounts checked?” or “What would I inspect before changing this validation rule?” A focused question gives you a reason to open one file and a reason to move to the next.
Search for names in routes, exports, configuration and tests. Treat those matches as starting candidates, not proof of responsibility. A file called auth may only configure a library; the decision you need may live elsewhere.
- Write down the question.
- List the source files that seem relevant.
- State what would count as a supported answer.
2. Map the structure around those files
Inspect a file's direct imports and the files that import it. Follow a short route through related files. If the route branches, make the branch explicit instead of pretending there is one continuous execution path.
A source-import graph establishes structural dependencies. It does not establish which function calls another, the order requests take at runtime, or whether an imported module is exercised in production. Dynamic loading, framework conventions and external consumers may require additional investigation.
In a monorepo, preserve package boundaries. A directory can be a useful area to investigate without being a separately deployed service or a verified business domain.
3. Read what the source actually establishes
For a relevant declaration, inspect its inputs, return values, visible checks, error handling and delegation to dependencies. Ask what the excerpt establishes and what is still outside it.
Scroll the table horizontally to compare all three columns.
| Question | Evidence to inspect | What remains to confirm |
|---|---|---|
| What goes into this function? | Parameters, local reads and validation | Who supplies these values, and under which configuration? |
| What does it return or change? | Return statements and visible writes | Downstream interpretation and runtime side effects |
| Which conditions change the result? | Branches, guards and exception handling | Whether those conditions occur in the deployed system |
| Where should I read next? | Imports, declarations and related tests | Cross-file call relationships not established by imports |
Read associated tests for examples of intended behavior. The existence of a test file is not a coverage measurement, and reading its assertions is not the same as running it successfully.
4. Keep facts, interpretation and unknowns separate
A useful explanation links to the source that supports it. Record the repository revision where possible; line numbers from a moving branch can become misleading.
- Observed fact: this file imports a particular module, or a visible branch rejects a missing value.
- Interpretation: what that appears to mean for the part you are investigating.
- Unknown: the runtime configuration, intended business rule or external behavior you have not verified.
AI can help form an explanation, but a citation only gives you a place to check. It does not prove the reasoning is correct. Do not send private code to a provider without permission and suitable data-handling terms.
Ask a teammate a focused question with the references you already checked. That makes missing business context easier to resolve than asking for a tour of everything.
5. Try a small, reviewable change
Use the repository's normal development and review process to test your mental model. Before editing, predict which files and behaviors need inspection. Run the relevant tests and checks, and compare the results with your prediction.
If a security finding is involved, inspect the actual location, affected dependency and relevant conditions. Severity and import reach are useful context; neither proves exploitability or a complete risk assessment.
Do not equate the number of files opened, tour steps completed or notes generated with understanding. Look for whether the engineer can explain a concrete responsibility, choose a plausible implementation location and name what they still need to verify.
6. Leave a brief the next engineer can use
Keep the handover small enough to review. Include the investigation question, area boundary, relevant source references, tests examined, findings to investigate, decisions and open questions. Label generated interpretation and reader corrections separately.
Review exports for confidential information. Even an explanation that does not embed raw source can paraphrase sensitive implementation details.
Worked example: who can change a post?
Consider the Flaskr tutorial in Flask 3.1.2, commit 2c1b30d. Ask a narrow question: where does this sample check whether a reader may update or delete a post? This is an educational source-reading example, not an assessment generated by Xolvyn.
- Find the entry points. The update and delete views in
blog.pyboth uselogin_required, then callget_post(id)before changing the database. - Separate login from permission. In
auth.py, the decorator redirects wheng.useris missing. A request hook reads the session user ID and loads that user. This explains the login gate; it does not establish ownership of a post. - Read the shared guard.
get_postdefaultscheck_authorto true. It rejects a missing post with 404 and a different author ID with 403. The default matters: a caller can explicitly disable that author check, so inspect callers rather than assuming every use enforces ownership. - Check the intended cases. The upstream tests describe login redirects, non-author rejection and missing-post responses for these paths. Read those assertions, then run the tests in your own checked-out environment before relying on a passing result.
The resulting brief: in this revision, the two views share a login gate and a post-author guard. Start a change review in blog.py, follow the decorator into auth.py, and inspect the relevant tests. An import edge alone would not establish any of those checks.
How this example was checked
The cited files and assertions were inspected at the fixed revision on 5 November 2026. The upstream tests were not executed for this article. This reading does not verify a deployed application, session configuration or a complete security boundary. The official Flask blog tutorial provides the wider teaching context; the commit links above preserve the exact example.
Xolvyn is preparing a workspace for this kind of investigation: reading routes, source-file dependency maps, area briefs and security findings in context. Join the waitlist to hear about availability. This guide is not evidence of a measured onboarding-speed improvement.