The Setup Audit Trail is a built-in log of every metadata change made in Setup — who, when, and what. It's the answer to "who changed this and when did it break?".
It captures things like: a user adding/editing a field, modifying a profile or permission set, changing a sharing rule, activating a flow, deploying a change set, modifying an Apex class. It does NOT capture data changes (use Field History Tracking for that) or runtime events like report exports (use Event Monitoring).
Setup -> Setup Audit Trail. View the last 6 months of changes inline; export the last 6 months as a CSV; for longer retention, use Salesforce Shield's Audit Trail Export Dashboard which extends to 18 months.
Practical uses:
- "When did our validation rule last change?" — search for "validation rule" filtered by section.
- Investigating a regression — match the timestamp of a bug appearing to recent setup changes.
- Compliance — exportable evidence for SOX or similar audits.
Limitation: 6-month visibility window; older changes are gone unless exported. If you have audit obligations, schedule monthly exports to your archive.