06-command-line-tool.md

Command Line Tool

The json-schema CLI does two things: check that a schema is valid (lint), and emit pre-compiled validator code (gen-validator).

Install

go install github.com/lestrrat-go/json-schema/cmd/json-schema@latest

lint — validate a schema document

Parses a schema and compiles it, reporting any structural or semantic problem. Reads a file, or - for stdin.

json-schema lint schema.json
# Schema schema.json is valid

echo '{"type": "string"}' | json-schema lint -
# Schema stdin is valid

If the document is not a valid schema or cannot be compiled, lint prints the error and exits non-zero — handy as a pre-commit or CI check on schema files.

gen-validator — emit validator code

Compiles a schema and prints Go source that rebuilds the validator directly, so production code can skip compilation. Reads a file or - for stdin.

json-schema gen-validator --name UserValidator user-schema.json

--name sets the generated variable name (default val). See Code Generation for a full example of the output and how to wire it into go:generate.

# from stdin, default variable name "val"
echo '{"type":"string","minLength":1}' | json-schema gen-validator -
# val := validator.String().MinLength(1).MustBuild()

Summary

Command	Purpose	Key flag
lint [file|-]	Verify a schema is valid	—
gen-validator [file|-]	Print Go validator code	--name <var> (default val)