aiohttp Client
Async HTTP client (and server) for Python using asyncio. aiohttp's ClientSession makes async HTTP requests with connection pooling, streaming, WebSocket support, and cookie management. The standard for async HTTP in Python before httpx's rise. Still widely used for WebSocket connections (aiohttp supports WS natively), streaming downloads, and legacy async codebases.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
TLS/SSL configurable with ssl.SSLContext. Certificate verification on by default. Client certificate auth supported. aio-libs maintains regular security patches.
⚡ Reliability
Best When
You need native WebSocket support or are maintaining existing aiohttp async code — aiohttp's WS support is mature and widely deployed.
Avoid When
Starting a new async Python project without WebSocket requirements — use httpx for its cleaner API and sync/async consistency.
Use Cases
- • Make async HTTP calls from agent services with connection pooling — aiohttp's ClientSession reuses connections for efficient batched API calls
- • Establish WebSocket connections for real-time agent communication — aiohttp supports ws:// and wss:// with full bidirectional messaging
- • Stream large agent responses (LLM streaming, file downloads) with aiohttp's async streaming without buffering full response in memory
- • Build agent HTTP clients with cookie-based session management for web automation that requires login state
- • Use aiohttp's TCPConnector for connection limit control in high-concurrency agent HTTP workloads
Not For
- • Modern async HTTP for new code — httpx is now preferred for its cleaner API and sync/async parity; aiohttp for legacy compatibility and WebSocket use cases
- • Sync Python code — aiohttp requires asyncio; use requests or httpx-sync for synchronous HTTP
- • Simple one-off requests — httpx or even urllib.request is simpler for non-session HTTP calls
Interface
Authentication
Auth via headers or aiohttp.BasicAuth. No built-in OAuth. Token injection via headers dict or connector. Supports client-side TLS certificates.
Pricing
Open source aio-libs project. Apache 2.0 license.
Agent Metadata
Known Gotchas
- ⚠ ClientSession must be used as async context manager or explicitly closed — creating session in async function without closing leaks connections; use 'async with aiohttp.ClientSession() as session'
- ⚠ Response body must be consumed within the request context manager — accessing response text after 'async with session.get() as response' block closes raises RuntimeError
- ⚠ aiohttp does NOT raise exceptions on non-2xx responses by default — must call response.raise_for_status() explicitly or check response.status; silent 4xx responses are a common agent bug
- ⚠ DNS caching: aiohttp reuses DNS lookups within a session — if the target service scales horizontally, old DNS entries may bypass load balancers; configure ttl_dns_cache=0 to disable
- ⚠ Total timeout vs connect timeout: aiohttp.ClientTimeout has separate total, connect, sock_connect, and sock_read — failing to set total timeout means individual operations can hang indefinitely
- ⚠ WebSocket message size limit defaults to 4MB — large agent messages (embeddings, documents) exceed this limit and raise WebSocketError; configure max_msg_size on WS connection
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for aiohttp Client.
Scores are editorial opinions as of 2026-03-06.