A short one — this time about a colleague’s work worth sharing.

Yury Usishchev built validgo-gen — an OpenAPI 3.0 → Go code generator focused on the one thing Go’s JSON handling is notoriously bad at: input validation.

The core problem: after json.Unmarshal, a missing field, an explicit null, and an empty "" all collapse into the same zero value. Your handler can’t tell them apart — and for a strict API contract, those are three very different cases.

validgo-gen solves it with two-layer validation:

  • Pre-deserialization — inspects raw JSON before unmarshaling: missing required fields and invalid nulls get caught while they’re still distinguishable.
  • Post-deserialization — go-playground/validator struct tags (min, max, oneof, email, unique) on the resulting structs.

What I like about the generated code:

  • chi integration — plugs into existing middleware, no custom runtime lock-in.
  • Per-operation interfaces — clean dependency injection instead of one giant server interface.
  • Idiomatic types — *string for optionals, decimal.Decimal, time.Time. No Java-flavored Go.
  • Built via go/ast — output is valid, gofmt-compliant Go by construction, not by template luck.

If you’ve been burned by oapi-codegen (no validation), ogen (non-standard runtime coupling), or openapi-generator (Java-style everything) — give it a look.