Go API Validation

API validation usually needs more than a boolean result. Clients need field paths, readable messages, and predictable JSON output. Valgo builds those results from validation sessions.

Validate a request payload

Use Is(...) when you want each validator chain to stop after the first failed rule:

val := v.Is(
  v.String(input.Email, "email").Not().Blank().Email(),
  v.String(input.Password, "password").Not().Blank().LengthBetween(8, 72),
)

Use Check(...) when you want to collect multiple messages from the same chain:

val := v.Check(
  v.String(input.Password, "password").Not().Blank().LengthBetween(8, 72),
)

Return structured errors

Valgo can convert a validation session to an error, inspect messages, or produce structured output for JSON responses.

if err := val.ToError(); err != nil {
  return err
}

See Go Validation Errors and JSON Output for output options and Go Sign-up Form Validation for a complete request-style example.

Nested API payloads

For nested JSON payloads, use namespaces to create stable paths:

val := v.Is(
  v.In("address",
    v.String(input.Address.City, "city").Not().Blank(),
  ),
)

For arrays or repeated fields, see Validate Go Slices and Indexed Errors.