Verified against Claude Code · 2026-07-15
Get a new codebase explained top-down before you touch a line
An onboarding prompt that forces a layered, top-down explanation of an unfamiliar codebase — entry point, architecture, data flow, then the non-obvious traps — instead of a flat file-by-file dump.
The prompt
Ready to copy — highlighted parts are example details you can swap.
You are onboarding a new engineer onto this codebase. Assume they can read code but have zero context on this project's specific decisions. Do not describe syntax. Describe intent, architecture, and traps. SCOPE the checkout and payment flow EXPLAIN IN THIS ORDER 1. What does this codebase do, in two sentences, for someone who has never seen it? 2. Entry point or points — where does execution actually start, and what is the first meaningful thing that happens? 3. Architecture — the four to six major modules or layers and, for each, its one job and what it explicitly does not do. 4. Data flow — trace one realistic request or action end to end through those layers, naming real files. 5. State and side effects — what is stateful, where, and what breaks if two of those run concurrently? 6. The traps — the three to five things that look obvious but are not: a naming choice that is misleading, a module that looks unused but is not, a place where the easy fix is actually wrong. CONSTRAINTS - Cite real file paths and function or class names, not generic descriptions. - If you are inferring rather than certain because no comment or doc confirms it, say "likely" or "appears to." Do not present a guess as fact. - Stop after item 6. Do not propose changes or improvements unless asked.
Customize the highlighted detailsoptional — the prompt above already works
Why this works
Given a bare explain this codebase request, models default to a flat, file-by-file recap because that is the path of least resistance through the context window, not because it is the most useful shape — it burns the reader's attention without building a mental model. Fixing the traversal order from entry point to architecture to data flow to statefulness to traps exploits the model's real strength, synthesizing many files into a structure, while removing the choice of shape that produces the flat dump. The step asking what looks obvious but is not matters specifically because a generic explain this prompt optimizes for describing what the code does, which the model can already do from the code alone; asking for what is non-obvious forces it to reason about what would mislead a newcomer, which is the actual value an onboarding document needs to deliver. The explicit instruction to say likely rather than present a guess as fact matters because codebase explanations are exactly the kind of task where a fluent, confident-sounding wrong claim about why a module exists is more dangerous than an admitted gap.
Verified against
Claude Code Sonnet 4.6 · 2026-07-15
Changelog
- 2026-07-15 — Initial publish, verified against Claude Code (Sonnet 4.6).
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