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
Decision gist · record as of 2026-08-14
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.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.10 or later; all calls are async and must be awaited.
- Low install friction with a pure Python wheel.
- Active maintenance with a recent release on 2026-08-13; the repository shows current activity.
License · maintenance · safety
Apache-2.0 (permissive) — Apache-2.0 permissive license allows commercial and private use with minimal restrictions.
last release 2026-08-13 (1 days) · last repo commit 2026-08-13 · 4 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 10,253,945 downloads/mo, #1,465 on PyPI
Alternatives
Verify before relying
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(...)- 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.
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 on it.
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
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.
Requires Python 3.10 or later; all calls are async and must be awaited.
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(...)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 the current Python release >=3.10 |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | 2 packagesfastcorefasttransport |
| Maintenance | Actively maintained 1 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 10,253,945 / month, #1,465 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Programming Language :: Python :: 3Programming Language :: Python :: 3 :: Only |
Evidence: fastspec-0.2.1-py3-none-any.whl
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See also openapi3 · spectree · daytona_analytics_api_client_async · ogx_open_client · daytona_toolbox_api_client_async · apispec · flask-pydantic-spec · prance · openapi-python-client · neptune-api