---
id: fastspec
version: "0.2.1"
license: Apache-2.0
license_treatment: permissive
maintenance: active
---

# fastspec — Dynamic OpenAPI, Discovery, and GraphQL spec client for Python — turn any API spec into a fully-typed async client with attribute chaining, streaming, and file uploads

License: permissive · Maintenance: active · Downloads: 10.3M/mo

## What it is and what it does

fastspec is a client generator that reads OpenAPI (JSON/YAML) or Google Discovery API specifications and automatically builds a fully async Python client. Instead of hand-writing HTTP calls or maintaining generated code, you load a spec, instantiate a client with auth headers, and call endpoints using attribute chaining—the library handles parameter validation, serialization, streaming, and file uploads transparently.

The package is built on fastcore and fasttransport, providing a lightweight async foundation. It's designed for developers who work with multiple APIs and want to avoid boilerplate; the same pattern works across any spec-compliant API. Operations are discovered at runtime and organized into logical groups, so you can explore available endpoints programmatically.

Use it for:

- Build a unified async client for LLM APIs without hand-writing request code.
- Quickly prototype integrations with REST APIs using their published specs.
- Stream responses from APIs that support streaming with a single flag.
- Upload files to APIs while keeping the client code simple and type-aware.
- Dynamically generate clients for internal or third-party APIs when specs are available.

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

Converts OpenAPI and Google Discovery API specs into fully async Python clients with attribute chaining, streaming, and file upload support.

Yes, if you work with multiple spec-compliant APIs and want to eliminate boilerplate client code. The low install friction, active maintenance, permissive Apache-2.0 license, and no known vulnerabilities make it a safe choice. The async-first design and support for streaming and file uploads cover real API patterns. Start with it if you're building integrations with services that publish OpenAPI or Google Discovery specs.

## Install

pip install fastspec
uv add fastspec
poetry add fastspec

## Installing fastspec

Before you install: Low install friction with a pure Python wheel. Active maintenance with a recent release on 2026-08-13; the repository shows current activity.

License in practice: Apache-2.0 permissive license allows commercial and private use with minimal restrictions.

Quickstart:

pip install fastspec

from fastspec.oapi import OpenAPIClient
from fastspec.spec import SpecParser

spec = SpecParser.from_openapi(spec_dict)
client = OpenAPIClient(spec, headers={"Authorization": "Bearer token"})
# await client.resource.operation(...)

Requires Python 3.10 or later; all calls are async and must be awaited.

Verify before relying:

- Whether the package handles all OpenAPI versions or has known compatibility gaps.
- Performance characteristics when working with very large specs or many concurrent requests.
- Quality of error messages and debugging experience when API calls fail.
- How file uploads are handled across different API specs and content types.

## Package facts

- License: Apache-2.0 (permissive)
- Python support: supports_current
- Install friction: low
- Maintenance: active
- Downloads: 10.3M/month (top 5,000 on PyPI)
- Known vulnerabilities: none known

## Tags

openapi client generator, api spec to python client, async api client from spec, google discovery client, dynamic api client builder, openapi python async, spec-driven http client, api-client, openapi, async

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