aiohttp
Async HTTP client/server framework for Python — provides both aiohttp.ClientSession for HTTP client and aiohttp.web for HTTP server with WebSocket support. aiohttp features: ClientSession with connection pooling/reuse, concurrent requests, streaming uploads/downloads, WebSocket client and server, TCPConnector for DNS caching and SSL, multipart, cookie jars, middleware, signal handlers, route-based request handling, aiohttp.web Application for building REST APIs, and comprehensive error handling. Battle-tested for high-throughput async scenarios.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
HTTP library. SSL verification on by default. Do not set ssl=False in production. aiohttp.web server: validate all input, use proper CORS headers, rate limit endpoints. WebSocket server: validate origin header. Cookie handling is automatic — protect session cookies.
⚡ Reliability
Best When
High-throughput async HTTP clients and WebSocket connections — aiohttp excels at concurrent scraping, WebSocket servers, and high-volume async HTTP workloads.
Avoid When
Synchronous code (use requests/httpx sync), production REST APIs (use FastAPI), or when httpx's simpler API suffices.
Use Cases
- • Agent async HTTP client — async with aiohttp.ClientSession() as session: async with session.get(url, timeout=aiohttp.ClientTimeout(total=30)) as resp: resp.raise_for_status(); data = await resp.json() — async client; agent makes non-blocking HTTP requests; ClientSession reuses connections; raise_for_status() for error checking
- • Agent concurrent requests — async with aiohttp.ClientSession() as session: tasks = [session.get(url) for url in urls]; responses = await asyncio.gather(*tasks); results = [await r.json() for r in responses] — concurrent; agent fetches multiple URLs simultaneously; gather() runs all tasks concurrently; connection pooling handles backend limits
- • Agent WebSocket client — async with aiohttp.ClientSession() as session: async with session.ws_connect(ws_url) as ws: await ws.send_str(json.dumps(msg)); async for msg in ws: if msg.type == aiohttp.WSMsgType.TEXT: handle(msg.data) — WebSocket; agent maintains persistent WebSocket connection; handles reconnection; msg.type checks TEXT/BINARY/CLOSE
- • Agent streaming download — async with aiohttp.ClientSession() as session: async with session.get(url) as resp: async for chunk in resp.content.iter_chunked(8192): await write_chunk(chunk) — streaming; agent downloads large files without memory accumulation; iter_chunked for binary; iter_any for available data; readline for text streams
- • Agent lightweight REST server — app = aiohttp.web.Application(); async def handler(request): data = await request.json(); return aiohttp.web.json_response({'result': process(data)}); app.router.add_post('/process', handler); aiohttp.web.run_app(app, host='0.0.0.0', port=8080) — server; agent exposes webhook endpoint
Not For
- • Production web frameworks — aiohttp.web is capable but FastAPI/Starlette have better ecosystem, OpenAPI, and type support for production APIs
- • Synchronous code — aiohttp requires async/await throughout; for sync HTTP use requests or httpx sync client
- • Simple scripts — aiohttp's async context managers add boilerplate; httpx has simpler API for both sync and async
Interface
Authentication
No auth — HTTP library. Supports BasicAuth via aiohttp.BasicAuth, bearer token via headers, custom auth.
Pricing
aiohttp is Apache 2.0 licensed. Free for all use.
Agent Metadata
Known Gotchas
- ⚠ ClientSession must be created inside async context — creating ClientSession() outside async function causes DeprecationWarning in 3.x and may fail; agent code: always create inside async function or async with block; do not create at module level; one session per application lifetime (reuse), not per request
- ⚠ Timeout uses ClientTimeout not seconds — aiohttp.ClientTimeout(total=30) not just 30; session.get(url, timeout=30) is deprecated; agent code: timeout = aiohttp.ClientTimeout(total=30, connect=10); session.get(url, timeout=timeout); total= is end-to-end; connect= is connection establishment only
- ⚠ resp.json() must be awaited — async with session.get(url) as resp: data = resp.json() is WRONG — missing await; must be: data = await resp.json(); same for resp.text(), resp.read(); forgetting await returns coroutine object not data; agent code: always await response content methods
- ⚠ Response consumed only once — once resp.text() or resp.json() awaited, content is consumed; calling again raises aiohttp.ClientPayloadError; agent code needing to read body twice: content = await resp.read(); then json.loads(content.decode()); or text = await resp.text(); then json.loads(text)
- ⚠ TCPConnector must be shared across sessions — creating new TCPConnector per session defeats connection pooling; agent code: connector = aiohttp.TCPConnector(limit=100); session = aiohttp.ClientSession(connector=connector); share one connector; set connector_owner=False if session should not close connector on session close
- ⚠ raise_for_status() must be called explicitly — aiohttp does NOT raise on 4xx/5xx by default; resp.status is the status code; agent code: always call resp.raise_for_status() inside response context manager; or check: if not resp.ok: handle_error(); raise_for_status() only available inside 'async with session.get() as resp:' block
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Scores are editorial opinions as of 2026-03-06.