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First day codebase tour

Paste a file tree and a few key files and get the tour a senior engineer would give you: how a request flows, where things live, what to avoid.

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Claude Fable 5.1
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The prompt

Pretend you've maintained this codebase for three years and I joined the team this morning.

Here's the file tree:
```
[PASTE THE OUTPUT OF: tree -L 3 -I node_modules]
```

And the files that matter most:
[PASTE 2 TO 5 FILES: the entry point, a core model, one typical route or handler]

Walk me through it:
1. What does this system do, and how is it put together? One paragraph.
2. Pick one typical request and follow it from the entry point to the database and back. Use the real file and function names.
3. Which five concepts do I need in my head, and how do they connect?
4. Give me a table: "I want to change X" on the left, "look in Y" on the right.
5. What looks wrong but is on purpose? And what really is wrong?
6. Suggest three small, safe tasks for my first week that would teach me the most.

If what I pasted isn't enough to answer something, tell me which file you need. Don't guess.
  • onboarding
  • architecture
  • code-reading

What it generates

Example

In one paragraph. This is a bookings app for small gyms. A React front end talks to an Express API in /server. Data lives in Postgres and is accessed through Prisma. Anything slow (emails, PDF invoices) goes through a job queue in /jobs so that requests stay fast.

One request, start to finish: a member books a class

  1. web/src/pages/ClassPage.tsx calls POST /api/bookings.
  2. server/routes/bookings.ts validates the body with bookingSchema, then calls canBook(member, class).
  3. server/services/bookings.ts opens a transaction, checks the class is not full, and inserts the row.
  4. It queues a booking-confirmed job and returns 201.
  5. jobs/bookingConfirmed.ts sends the email a few seconds later.

Where things live

I want to change... Look in
Who is allowed to do what server/auth/policies.ts
An email jobs/emails/*.mjml
The database schema prisma/schema.prisma, then run migrate dev
Prices and plans server/config/plans.ts (not the database)

Looks wrong, is on purpose

  • Every table has deletedAt. Nothing is ever really deleted, so always query through db.active().
  • Class capacity is checked twice, in the route and inside the transaction. The second check stops two people taking the last spot.

Really is wrong

  • utils/dates.ts mixes UTC and local time. Do not build on it. There is a ticket.

Your first week

  1. Add the missing index listed in TODO.md. You will learn how migrations work here.
  2. Add the class location to the confirmation email. It touches the whole path above.
  3. Write tests for canBook(). There are edge cases nobody has written down.

I could not see how payments work from these files. Send me server/services/billing.ts and I will add it to the tour.

NoteThis is an example. Results change between runs and model versions. Claude Prompts is a fan project and is not affiliated with Anthropic.

Getting the most from this prompt

When it helps

Your first days in a repository you didn't write. A new job, an open source project you'd like to contribute to, a codebase somebody left you. It's also a quick way to produce onboarding notes for whoever joins after you.

What to paste

The file tree does more work than you'd think. Keep it to three levels and leave out build output, or the structure drowns in noise. For the files, go for the ones that show the pattern rather than the biggest ones: an entry point, one model, one ordinary route. Once you have the tour, ask for the walkthrough again with a different action ("now trace a failed login") and you'll see the error paths too.

Take it with a pinch of salt

Claude only knows what you pasted. Treat the "really is wrong" list as things to ask a teammate about, not as facts. And whatever else you change in the prompt, keep the last line. Naming the missing file instead of guessing is what makes the tour trustworthy.

How to use this prompt

  1. [01] Copy

    Copy the prompt

    Use the copy button above. The full text is included, nothing is cut off.

  2. [02] Fill in

    Replace the yellow parts

    Everything highlighted in yellow is a placeholder. Swap it for your own topic, audience or data.

  3. [03] Vote

    Run it in Claude and vote

    If the result helped, press the heart. Votes decide which prompts make the weekly top 10.

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