1# Understand large codebases | Codex use cases1# Understand large codebases | Codex use cases
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3Codex 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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5Copy page [Export as PDF](https://developers.openai.com/codex/use-cases/codebase-onboarding/?export=pdf)30Copy page [Export as PDF](https://developers.openai.com/codex/use-cases/codebase-onboarding/?export=pdf)
28 - the top gotchas to watch for before making changes53 - the top gotchas to watch for before making changes
29 End with the files I should read next.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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31Explain 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.
32 Include:59 Include:
33 - which modules own what60 - which modules own what