Validation and CI

Generate validation methods

Add --validate to both the generation directive and the scaffold command:

//go:generate go tool gen-jsonschema --validate

go tool gen-jsonschema new \
  -out schema.go \
  -methods 'ToolInput=Schema' \
  --validate \
  --generate
go mod tidy

The generated ValidateJSON([]byte) error compiles the schema once at startup. Validation covers required fields, types, unknown properties, enum membership, and nested structure. Schema-validation failures can be inspected as *jsonschemav6.ValidationError; malformed JSON may instead return a parsing error.

import (
    "errors"
    "log"

    jsonschemav6 "github.com/santhosh-tekuri/jsonschema/v6"
)

func validateToolInput(data []byte) error {
    if err := (ToolInput{}).ValidateJSON(data); err != nil {
        var validationErr *jsonschemav6.ValidationError
        if errors.As(err, &validationErr) {
            log.Printf("invalid field: %s", validationErr.InstanceLocation)
        }
        return err
    }
    return nil
}

Fail CI on drift

JSONSCHEMA_NO_CHANGES flows through every go generate directive and makes the generator fail without writing schema files when schema JSON would change. Generation can still update jsonschema_gen.go when schemas are unchanged, so pair the command with a Git diff:

- name: Check generated schemas
  run: JSONSCHEMA_NO_CHANGES=1 go generate ./... && test -z "$(git status --porcelain)"

For repositories with generators that do not understand JSONSCHEMA_NO_CHANGES, use the broader fallback:

- name: Check all generated files
  run: go generate ./... && test -z "$(git status --porcelain)"

Run go test ./... after the drift check so tests execute against the same generated state that will be committed.