P0 and P1 severity

Last updated 2 October 2026.

What do P0 and P1 mean?

P0 and P1 are the two highest severities a code review finding can have: P0 is critical, such as a security hole, data loss or a crash on a main path, and P1 is high, such as a feature that does not work.

In MergeSafe

• P0 Critical and P1 High block a merge and fail the mergesafe-review check.
• P2 Medium and P3 Low never block.
• A disputed P0 or P1 is withdrawn or downgraded to P3.

Examples of each: Severity: P0, P1, P2 and P3.

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