fastapi-code-generator

Generate a FastAPI application from an OpenAPI document.

📣 💼 Maintainer update: Open to opportunities. 🔗 koxudaxi.dev

Documentation

The docs site is the source of truth for user-facing documentation:

• Overview
• CLI Reference
• Supported Formats
• Development & Contributing

Use this README as a quick start. The full examples, templating details, and development workflow live in docs/.

Installation

uv tool install fastapi-code-generator

pip install fastapi-code-generator

Quick Start

fastapi-codegen --input openapi.yaml --output app --output-model-type pydantic_v2.BaseModel

fastapi-code-generator uses datamodel-code-generator to build the model layer. See the overview guide for a complete end-to-end example, custom templates, custom visitors, and router generation.

Command Help Snapshot

This block is generated from the current CLI so the README and docs overview stay aligned. For tested option scenarios and examples, use the CLI reference page.

Usage: fastapi-codegen [OPTIONS]

Options:
  -e, --encoding TEXT             [default: utf-8]
  -i, --input TEXT                [required]
  -o, --output PATH               [required]
  -m, --model-file TEXT
  -t, --template-dir PATH
  --model-template-dir PATH
  --enum-field-as-literal [all|one|none]
  -r, --generate-routers
  --specify-tags TEXT
  -c, --custom-visitor PATH
  --disable-timestamp
  --strict-nullable               Respect explicit OpenAPI nullable flags when
                                  generating models.
  --include-request-argument      Auto-inject a FastAPI Request parameter into
                                  operations when not present.
  -d, --output-model-type [pydantic_v2.BaseModel|pydantic_v2.dataclass|dataclasses.dataclass|typing.TypedDict|msgspec.Struct]
                                  [default: pydantic_v2.BaseModel]
  -p, --python-version [3.10|3.11|3.12|3.13|3.14]
                                  [default: 3.10]
  -V, --version
  --use-annotated                 Use typing.Annotated for generated model
                                  field constraints.
  --reuse-model                   Reuse identical generated models as the same
                                  type.
  --enable-faux-immutability      Generate frozen Pydantic models so instances
                                  are hashable when their fields are hashable.
  --install-completion            Install completion for the current shell.
  --show-completion               Show completion for the current shell, to
                                  copy it or customize the installation.
  --help                          Show this message and exit.

Common Tasks

• Generate a single-file app from an OpenAPI spec: fastapi-codegen --input openapi.yaml --output app
• Generate router modules for larger applications: fastapi-codegen --input openapi.yaml --output app --template-dir modular_template --generate-routers
• Limit router regeneration to specific tags: fastapi-codegen --input openapi.yaml --output app --template-dir modular_template --generate-routers --specify-tags "Wild Boars, Fat Cats"
• Target Pydantic v2 output: fastapi-codegen --input openapi.yaml --output app --output-model-type pydantic_v2.BaseModel

Further Reading

• Overview for the full walkthrough and generated output example
• CLI Reference for option-by-option behavior and tested scenarios
• Supported Formats for the generated support matrix
• Development & Contributing for the local workflow and docs maintenance steps