WebSocket vs HTTP - Key Differences

WebSocket and HTTP are both communication protocols that run over TCP, but they serve different purposes. When comparing HTTP vs WebSocket, the core difference is clear: HTTP uses a request-response model where the client always initiates communication. WebSocket establishes a persistent connection where both sides can send data at any time.

This distinction drives everything: performance characteristics, infrastructure requirements, and the types of applications each protocol is suited for.

How HTTP Communication Works

HTTP is a stateless, request-response protocol. The client sends a request, the server processes it and sends a response.

Client              Server
  |--- GET /data ---->|
  |<-- 200 OK --------|
  |                    |
  |--- POST /data --->|
  |<-- 201 Created ---|

Every interaction follows the same pattern:

The client opens a TCP connection (or reuses one via keep-alive).
The client sends a request with headers (method, path, host, content type, cookies, authorization, and more).
The server processes the request and sends a response with its own headers.
The server cannot send data unless the client asks for it.

HTTP headers on a typical API request add 200 to 800 bytes of overhead. For a small JSON payload of 50 bytes, the headers can be 10x larger than the actual data.

HTTP/2 and HTTP/3

HTTP/2 introduced multiplexing (multiple requests over one connection), header compression (HPACK), and server push. HTTP/3 uses QUIC instead of TCP for faster connection setup and better handling of packet loss.

These improvements reduce overhead and latency for traditional request-response workloads. But they do not change the fundamental model. The server still cannot send arbitrary data to the client without a request. HTTP/2 server push was designed for pushing related resources (CSS, JS files) alongside HTML, not for real-time data streaming. Most browsers have removed support for it. If you need bidirectional communication, HTTP/2 WebSocket connections still require the upgrade handshake just like HTTP/1.1.

How WebSocket Communication Works

WebSocket HTTP connections start with an HTTP handshake, then upgrade to a persistent bidirectional connection:

Client              Server
  |--- HTTP Upgrade -->|    (one-time handshake)
  |<-- 101 Switching --|
  |                    |
  |<=== data =========>|   (bidirectional, any time)
  |<=== data =========>|
  |<=== data =========>|

After the handshake completes:

No HTTP headers are sent with each message.
Either side can send data at any time without waiting.
The connection stays open until one side explicitly closes it.
Messages are sent as lightweight frames with 2 to 14 bytes of overhead.

Side-by-Side Comparison

Feature	HTTP	WebSocket
Communication model	Request, then response	Bidirectional
Connection lifetime	Short-lived or keep-alive	Persistent
Who can initiate data	Client only	Both client and server
Per-message overhead	200-800 bytes (headers)	2-14 bytes (frame header)
Latency for updates	Higher (new request each time)	Lower (connection stays open)
Protocol prefix	`http://` or `https://`	`ws://` or `wss://`
Caching	Yes (CDN, browser, proxy)	No
Stateless	Yes (by design)	No (connection has state)
Load balancing	Straightforward	Requires sticky sessions
Firewall/proxy support	Universal	May need configuration
Binary data	Yes	Yes
Compression	gzip, brotli (standard)	Per-message deflate (extension)

Performance: Measured Differences

Per-Message Overhead

A typical HTTP request includes headers like this:

GET /api/messages HTTP/1.1
Host: chat.example.com
Accept: application/json
Authorization: Bearer eyJhbGciOiJIUzI1NiIs...
Cookie: session=abc123; preferences=dark
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64)
Accept-Encoding: gzip, deflate, br
Connection: keep-alive

This adds roughly 400 bytes before any payload. Every single request carries similar headers, even if the payload is just {"status":"ok"}.

A WebSocket frame carrying the same payload:

[2 bytes frame header] + [4 bytes mask (client only)] + [payload]

That is 6 bytes of overhead from client to server, 2 bytes from server to client. For applications exchanging hundreds of messages per second, this difference adds up fast.

Latency

HTTP requests incur latency from:

TCP connection setup (1 round trip, or 0 with keep-alive)
TLS handshake (1-2 round trips, or 0 with session resumption)
Request/response round trip (1 round trip minimum)

WebSocket incurs connection setup latency once. After that, sending a message requires no round trip for connection or header negotiation. The message goes directly into the existing TCP stream.

For a client sending 100 small messages per second:

HTTP polling: 100 full request-response cycles. Even with keep-alive, each requires sending and receiving headers. Approximately 40-80 KB of header overhead alone.
WebSocket: 100 small frames. Approximately 0.6-1 KB of total overhead.

Connection Setup Cost

Step	HTTP/1.1	HTTP/2	WebSocket
TCP handshake	Every request (without keep-alive)	Once	Once
TLS handshake	Every request (without keep-alive)	Once	Once
HTTP headers	Every request	Every request (compressed)	Only during handshake
Application data	After headers	After headers	Immediately

When HTTP Is the Better Choice

HTTP works best for interactions that follow the request-response pattern and do not need persistent connections.

REST and GraphQL APIs where the client requests specific data and the server responds. Fetching a user profile, submitting a form, querying a database. These operations are discrete and independent.

Static content delivery benefits from HTTP’s caching ecosystem. Browsers, CDNs, and reverse proxies can cache HTTP responses. WebSocket messages cannot be cached.

File uploads and downloads work well with HTTP’s built-in features: range requests for resumable downloads, multipart encoding for uploads, progress events, and content-length headers.

Server-rendered pages and SEO-critical content should be served over HTTP. Search engines crawl HTTP endpoints. They do not connect to WebSocket servers.

Webhook integrations between services use HTTP POST requests. The request-response model maps naturally to event delivery with acknowledgment.

Low-frequency data that changes every few minutes or less does not justify a persistent connection. A simple HTTP request every 30 seconds is easier to implement and maintain than a WebSocket connection.

When WebSocket Is the Better Choice

WebSocket excels when the application needs frequent, low-latency, bidirectional communication.

Chat and messaging where messages must be delivered instantly to all participants. The server needs to push new messages without waiting for clients to ask.

Live trading and financial data where prices change multiple times per second. Each update needs to reach the client with minimal delay.

Multiplayer games that synchronize game state between players in real time. Player positions, actions, and events need to be exchanged continuously.

Collaborative editing applications where every keystroke, cursor movement, or selection change is broadcast to other participants.

Live notifications and alerts that must appear immediately. Polling introduces a delay equal to the polling interval. WebSocket delivers notifications as soon as they happen.

IoT and telemetry from devices that report sensor readings frequently. The persistent connection avoids the overhead of setting up a new HTTP connection for each reading.

The Middle Ground: Server-Sent Events

If your application only needs server-to-client data push (no client-to-server messages beyond the initial request), consider Server-Sent Events (SSE).

Feature	HTTP Polling	SSE	WebSocket
Direction	Client to server	Server to client	Both
Implementation effort	Simple	Simple	Medium
Auto-reconnect	Manual	Built-in	Manual
Binary data	Yes	No (text only)	Yes
Works with HTTP/2	Yes	Yes	No (separate protocol)
CDN/proxy support	Full	Good	Needs configuration
Max connections per domain	6 (HTTP/1.1)	6 (HTTP/1.1), unlimited (HTTP/2)	No browser limit

SSE is a good fit for dashboards, notification feeds, and live content updates where the client just needs to receive data.

Common Mistakes

Using WebSocket for everything

Some developers default to WebSocket for all server communication. This adds complexity without benefit for standard API calls. Use HTTP for CRUD operations and WebSocket only where real-time bidirectional communication is needed.

Using HTTP polling when WebSocket would be simpler

On the flip side, if your polling endpoint is called every second and the data changes frequently, you are building a worse version of WebSocket with more overhead.

Ignoring connection management

WebSocket connections can drop silently due to network changes, proxy timeouts, or server restarts. Your client code needs reconnection logic with exponential backoff. HTTP requests fail explicitly and can be retried individually.

Forgetting about infrastructure

WebSocket connections are stateful. Load balancers need sticky sessions or a pub/sub layer (like Redis) to route messages correctly. HTTP requests are stateless and can be routed to any server.

Decision Guide

Use this flowchart to decide which protocol fits your use case:

Does the server need to send data without a client request?
- No: Use HTTP.
- Yes: Continue.
Does the client also need to send data to the server over the same connection?
- No: Use SSE.
- Yes: Continue.
Is the data high-frequency (multiple updates per second)?
- No: SSE or long polling may be enough.
- Yes: Use WebSocket.
Do you need binary data support?
- No: SSE works for text.
- Yes: Use WebSocket.

Many applications use both protocols. HTTP handles authentication, file uploads, and API calls. WebSocket handles the real-time features. This is a common and practical architecture.