supaschema and Squawk both improve PostgreSQL migration safety, and they are complementary rather than competing. Squawk is a free linter that analyzes migration SQL you have already written. supaschema generates the migration from declarative SQL and then runs its own replay-safety and lock-hazard checks.
Short answer
Use Squawk when you hand-write migration SQL and want a free lock-safety linter over it. Usesupaschema when you want the migration generated from declarative SQL files and checked in the same tool. You can also run both: generate and check with supaschema, then lint the rendered SQL with Squawk.
Comparison
| Capability | supaschema | Squawk |
|---|---|---|
| Generates migrations | Yes, from declarative SQL | No, lints SQL you provide |
| Lock-safety analysis | Yes (supaschema check) | Yes |
| Replay-safety guards (IF EXISTS, ON CONFLICT) | Yes | Partial, focused on lock and breaking-change rules |
| RLS policy body changes | Compared structurally | Not its focus |
| Generated types | TypeScript and Zod from the SQL tree | None |
| License | Free core (open) | Open source (MIT / Apache-2.0) |
| Database or Docker required | No | No |
Why the workflow differs
Squawk is a focused static linter: you point it at migration SQL and it flags dangerous operations such as table-lockingALTERs. It does not generate migrations or model the schema.
supaschema starts a step earlier. It diffs declarative SQL into a migration, then supaschema check applies replay-safety and lock-hazard rules to the result. Because supaschema also models the schema, it can compare RLS policy bodies structurally and generate TypeScript and Zod types from the same source.
The two are not mutually exclusive: if you already trust Squawk’s lint rules, you can keep running it over the SQL supaschema diff renders.
Last verified 2026-06-18 against the Squawk documentation and GitHub
repository. Confirm current behavior and licensing before relying on it.
Atlas lint is paid: free alternatives
Free Postgres migration-safety options, including Squawk and supaschema.
The check command
The replay-safety and lock-hazard diagnostics supaschema runs on each
migration.