toolkit

HTTP Request Flow

Runs in browser

Visualize network request lifecycle

Request

Secure (HTTPS)

Quick URLs (CORS-friendly):

Simulated Latencies

DNS Resolution 40-135ms
TCP Handshake 30-80ms
TLS Handshake 40-150ms
Server Processing 100-500ms

How to Use

Enter a URL and send a request.

You will see:

  • DNS Resolution Steps
  • TCP/TLS Handshake Timing
  • Server Processing & Response
Request Flow

Enter a URL and press Enter or click Send

Visualize DNS resolution, TCP/TLS handshakes, and server response

Related Tools

Simulators

TCP Handshake

Simulators

HTTP/2 Streams

Guides

How HTTPS Works

The Engineering of a Network Request

When you type a URL into your browser, it triggers a remarkably complex sequence of distributed systems operations. Before a single byte of HTML is rendered, your machine must navigate global DNS hierarchies, negotiate cryptographic secrets, and establish reliable byte-streams over an unreliable internet. This lifecycle defines Web Performance.

1. DNS Resolution (The Phonebook)

Computers route traffic using IP addresses (like 203.0.113.42), not human-readable domain names. The Domain Name System (DNS) acts as the internet's phonebook.

The Recursive Journey:
  1. Local Cache: Check browser → OS cache. (0ms)
  2. ISP Resolver: Query your local ISP's recursive resolver. (~15ms)
  3. Root Server (.): Queries the global root servers, which point to the TLD servers.
  4. TLD Server (.com): Queries the Top-Level Domain servers, which know who manages the root domain.
  5. Authoritative Name Server: The final server (e.g., Cloudflare, Route53) returns the exact A Record (IPv4) or AAAA Record (IPv6). (~40-100ms total)

2. The TCP 3-Way Handshake

Before HTTP data can flow, a reliable Transmission Control Protocol (TCP) connection must be formed. This ensures packets are delivered in order, without loss.

Step 1
SYN

Client asks to synchronize sequence numbers.

Step 2
SYN-ACK

Server acknowledges and synchronizes its own sequence.

Step 3
ACK

Client acknowledges. The socket is now established.

This handshake inherently takes exactly 1.5 Round Trip Times (RTT), bounded by the speed of light in fiber optic cables.

3. The TLS Handshake (HTTPS)

If connecting via HTTPS on port 443, a Transport Layer Security (TLS) handshake happens immediately after the TCP connection to encrypt the impending HTTP payload.

ClientHello: "I want to connect securely. I support these cipher suites."

ServerHello & Certificate: "Let's use AES-GCM. Here is my public key certificate proving I am the real website."

Key Exchange: The client encrypts a 'pre-master secret' using the server's public key. Both sides mathematically derive the same symmetric session key. The tunnel is now encrypted. (TLS 1.3 optimizes this to 1 RTT).

4. Server Processing & TTFB

The client finally sends the actual HTTP Request (e.g., GET /api/data HTTP/1.1). The server ingests it, queries databases, renders templates, and serializes a response.

Time To First Byte (TTFB)

This is a critical performance metric. TTFB is the total time from the user initiating the request to the browser receiving the very first byte of the HTTP response. High TTFB usually indicates slow database queries, struggling application servers, or network congestion. Optimal TTFB is heavily dependent on caching or deploying Content Delivery Networks (CDNs) near the end-user.

Further Reading