Skip to content

Output format

--output-format

Choose the command output format.

The default output format is text. Use json when another program or LLM agent should inspect structured output.

In normal generation mode, --output-format json wraps generated modules in a structured payload on stdout. If --output is also supplied, files are still written to disk and the JSON payload mirrors the generated files. --check also supports JSON output for difference reports. --watch keeps its existing text output contract and does not support --output-format json.

Structured JSON is emitted on stdout for successful commands and for --check difference reports. CLI usage errors, validation errors, and runtime generation errors continue to use text on stderr with a non-zero exit code.

Generation JSON includes the normalized requested output path in top-level output when --output is supplied, or null for stdout generation. files[].path is the output file name for single-file disk output, and the path relative to the output directory for directory output. For stdout-only single-file generation it is null, and for multi-module stdout generation it is the generated module path.

Use --output-format json with --generate-prompt to emit structured option metadata instead of Markdown. Use --output-format-json-schema when an LLM agent or tool needs the schema for a JSON payload.

Schema targets are intentionally scoped. generate-prompt emits the PromptPayload schema for --generate-prompt --output-format json. generation emits only the GenerationPayload schema for generated-file JSON. model-metadata emits the schema for files written by --emit-model-metadata. structured-output emits the broader StructuredOutputPayload schema, a union covering GenerationPayload, PromptPayload, CommandOutputPayload, and CheckOutputPayload. Structured payloads use kind as the discriminator.

Usage

datamodel-codegen --input schema.json --output-format text # (1)!
datamodel-codegen --input schema.json --output-format json # (2)!
datamodel-codegen --generate-prompt --output-format json # (3)!
datamodel-codegen --output-format-json-schema generation # (4)!
datamodel-codegen --output-format-json-schema generate-prompt # (5)!
datamodel-codegen --output-format-json-schema model-metadata # (6)!
datamodel-codegen --output-format-json-schema structured-output # (7)!
  1. Emit the default generated Python text
  2. Emit structured JSON containing generated files
  3. Emit structured JSON with current options and argparse metadata
  4. Emit JSON Schema for generated-file JSON output
  5. Emit JSON Schema for structured prompt JSON
  6. Emit JSON Schema for generated model metadata JSON
  7. Emit JSON Schema for any structured command JSON output
Generation JSON output 
{
  "version": 1,
  "format": "json",
  "kind": "generation",
  "output": null,
  "files": [
    {
      "path": null,
      "content": "# generated by datamodel-codegen:\n..."
    }
  ]
}
Prompt JSON output 
datamodel-codegen \
    --input schema.json \
    --output-model-type pydantic_v2.BaseModel \
    --generate-prompt "Choose strict model options." \
    --output-format json