fastspec

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 on this page — 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

fastspec on PyPI

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

Evidence: fastspec-0.2.1-py3-none-any.whl

Keywords: nbdev

Tags

More WWW/HTTP packages