1# Understand large codebases | Codex use cases1# Understand large codebases | Codex use cases
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9Codex use case
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11# Understand large codebases
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13Trace request flows, map unfamiliar modules, and find the right files fast.
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15Difficulty **Easy**
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17Time horizon **5m**
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19Use Codex to map unfamiliar codebases, explain different modules and data flow, and point you to the next files worth reading before you edit.
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21## Best for
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23 - New engineers onboarding to a new repo or service
24 - Anyone trying to understand how a feature works before changing it
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26# Contents
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3[← All use cases](https://developers.openai.com/codex/use-cases)28[← All use cases](https://developers.openai.com/codex/use-cases)
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30Copy page [Export as PDF](https://developers.openai.com/codex/use-cases/codebase-onboarding/?export=pdf)
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5Use Codex to map unfamiliar codebases, explain different modules and data flow, and point you to the next files worth reading before you edit.32Use Codex to map unfamiliar codebases, explain different modules and data flow, and point you to the next files worth reading before you edit.
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7Easy34Easy
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20## Starter prompt47## Starter prompt
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49Explain how the request flows through <name of the system area> in the codebase.
50 Include:
51 - which modules own what
52 - where data is validated
53 - the top gotchas to watch for before making changes
54 End with the files I should read next.
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56[Open in the Codex app](codex://new?prompt=Explain+how+the+request+flows+through+%3Cname+of+the+system+area%3E+in+the+codebase.%0A%0AInclude%3A%0A-+which+modules+own+what%0A-+where+data+is+validated%0A-+the+top+gotchas+to+watch+for+before+making+changes%0A%0AEnd+with+the+files+I+should+read+next. "Open in the Codex app")
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22Explain how the request flows through <name of the system area> in the codebase.58Explain how the request flows through <name of the system area> in the codebase.
23 Include:59 Include:
24 - which modules own what60 - which modules own what