HTTP Status Codes: Complete Reference Guide

Every HTTP request returns a status code that tells you exactly what happened. Understanding HTTP status codes is essential for web developers, API engineers, and anyone working with web scraping or proxy infrastructure. This complete reference guide covers every status code category with practical examples and troubleshooting tips.

What Are HTTP Status Codes?

HTTP status codes are three-digit numbers returned by a server in response to a client’s request. They are grouped into five classes based on the first digit, each indicating a different type of response.

1xx Informational Responses

These codes indicate the server has received the request and is continuing to process it.

2xx Success

Success codes confirm the request was received, understood, and accepted.

Checking Status Codes with cURL

# View the response status code
curl -o /dev/null -s -w "%{http_code}" https://example.com

View full response headers including status line
curl -I https://example.com

import requests

response = requests.get("https://example.com")
print(f"Status Code: {response.status_code}")
print(f"Reason: {response.reason}")

3xx Redirection

These codes indicate the client must take additional action to complete the request, usually following a redirect.

Handling Redirects

# Follow redirects automatically
curl -L https://example.com/old-page

Show redirect chain
curl -L -v https://example.com/old-page 2>&1 | grep "< HTTP\|< location"

Limit redirect depth
curl -L --max-redirs 5 https://example.com

import requests

Follow redirects (default behavior)
response = requests.get("https://example.com/old-page")
print(f"Final URL: {response.url}")
print(f"Redirect history: {[r.status_code for r in response.history]}")

Disable auto-redirect
response = requests.get("https://example.com/old-page", allow_redirects=False)
print(f"Status: {response.status_code}")
print(f"Location: {response.headers.get('Location')}")

4xx Client Errors

Client error codes indicate the request contains an error or cannot be fulfilled.

Common 4xx Fixes

# Debug 400 errors - check your request format
curl -v -X POST https://api.example.com/data \
-H "Content-Type: application/json" \
-d '{"key": "value"}'

Fix 401 - add authentication
curl -u username:password https://api.example.com/protected
curl -H "Authorization: Bearer YOUR_TOKEN" https://api.example.com/protected

Fix 407 - add proxy authentication
curl -x http://proxy:8080 --proxy-user user:pass https://example.com

5xx Server Errors

Server error codes indicate the server failed to fulfill a valid request.

Cloudflare-Specific Status Codes

Cloudflare uses custom 5xx codes for issues between Cloudflare and the origin server:

Status Code Decision Flowchart

When you encounter an error, follow this diagnostic approach:

1. Is it 4xx? → The problem is with your request. Check URL, headers, body, and authentication.
2. Is it 5xx? → The problem is on the server. Retry with exponential backoff.
3. Is it 3xx? → Follow the redirect or update your saved URL.
4. Is it 429? → You are being rate-limited. Slow down and add delays between requests.

Retry Logic for Server Errors

import requests
import time

def request_with_retry(url, max_retries=3, backoff_factor=2):
for attempt in range(max_retries):
response = requests.get(url)

if response.status_code == 200:
return response

if response.status_code in [429, 500, 502, 503, 504]:
wait_time = backoff_factor ** attempt
if response.status_code == 429:
# Check Retry-After header
retry_after = response.headers.get("Retry-After")
if retry_after:
wait_time = int(retry_after)
print(f"Got {response.status_code}, retrying in {wait_time}s...")
time.sleep(wait_time)
else:
response.raise_for_status()

raise Exception(f"Failed after {max_retries} retries")

Using Proxies to Handle Status Codes

Many 4xx errors (especially 403 and 429) occur because the server is blocking your IP. Using residential proxies can help bypass these blocks by rotating your IP address.

# Rotate through proxies to avoid rate limiting
curl -x http://user:pass@proxy.example.com:8080 https://target-site.com

FAQ

What is the most common HTTP status code?

200 OK is the most common status code, indicating a successful request. Among errors, 404 Not Found is the most frequently encountered.

What is the difference between 401 and 403?

A 401 Unauthorized means authentication is required but was not provided or is invalid. A 403 Forbidden means the server understood the request but refuses to authorize it, even with valid credentials.

How do I check HTTP status codes in a browser?

Open DevTools (F12), go to the Network tab, and reload the page. Each request shows its status code in the Status column.

What should I do when I get a 5xx error?

Server errors are usually temporary. Wait and retry with exponential backoff. If the error persists, contact the website administrator or check their status page.

Are HTTP status codes case-sensitive?

No. Status codes are numeric (three digits) and are not case-sensitive. The reason phrases (like “OK” or “Not Found”) are optional and can vary by implementation.