Backends¶

fastreq ships three pluggable HTTP backends behind one interface. They share the same surface so you can swap one for another without rewriting call sites.

Why three?¶

The right HTTP client depends on the target:

niquests — the required default. Best general performance, HTTP/2 built-in, both sync and async.
httpx — opt-in alternative for codebases that already use httpx everywhere.
curl_cffi — opt-in for TLS-fingerprint impersonation against sites that block plain HTTP clients.

All three implement the same [Backend][fastreq.backends.Backend] abstract class, so the rest of fastreq (concurrency gate, retry policy, rate limiter, proxy manager) is backend-agnostic.

The contract¶

Every backend implements the same three methods (see [Backend][fastreq.backends.Backend]):

class Backend(ABC):
    async def request(self, config: RequestConfig) -> NormalizedResponse: ...
    async def close(self) -> None: ...
    def supports_http2(self) -> bool: ...

Backends normalize their responses into a [NormalizedResponse][fastreq.backends.NormalizedResponse] that downstream code consumes uniformly. That means switching backends does not change return-type handling, retry behaviour, or response parsing.

Auto-detection¶

from fastreq import fastreq

results = fastreq(urls=["https://httpbin.org/get"], backend="auto")

backend="auto" (the default) selects niquests. niquests is a required dependency so it is always available; the other two are opt-in via extras.

Extra	Backend	Install
(none — core)	`niquests`	`pip install fastreq`
`httpx` (+ `h2`)	`httpx`	`pip install fastreq[httpx,h2]`
`curl`	`curl_cffi`	`pip install fastreq[curl]`

HTTP/2¶

Backend	HTTP/2 by default	Notes
`niquests`	✅	Always on for HTTPS endpoints
`httpx`	opt-in	Requires `pip install fastreq[h2]`
`curl_cffi`	✅	Via the impersonated browser's settings

When http2=True is requested but the backend does not support it, fastreq downgrades silently and logs at DEBUG level.

Browser impersonation (curl_cffi only)¶

Only the curl_cffi backend supports impersonate=. Pass a target like "chrome131", "safari184", or "random". See Impersonate a Browser.

from fastreq import fastreq

results = fastreq(
    urls=["https://finance.yahoo.com/quote/AAPL"] * 20,
    backend="curl_cffi",
    impersonate="chrome131",
    concurrency=10,
)

User-agent rotation is disabled automatically when impersonate is set, since curl_cffi supplies a matching UA.

Sync vs async¶

niquests supports both sync and async natively.
httpx and curl_cffi are async-only. fastreq's fastreq() sync wrapper runs the async client via asyncio.run for you, so both forms are exposed as a uniform API.

Removed backends¶

aiohttp and requests were removed in fastreq 3.0. Selecting either raises ConfigurationError with a migration hint:

BackendError: Backend 'aiohttp' is no longer supported in fastreq 3.0.
Use 'niquests' (default) or 'httpx' instead.
Install with: pip install fastreq[httpx]

When to choose which¶

Default to niquests for APIs and clean-network targets. Fastest, simplest.
Choose httpx if your codebase already speaks httpx or you need a transport that integrates with httpx's ecosystem (custom auth, retry helpers).
Choose curl_cffi when sites reject plain HTTP clients based on TLS fingerprint (Cloudflare / Akamai / Yahoo Finance style detection). Slowest of the three.