Learning Path
Debug HTTP Problems in Production
A pragmatic troubleshooting stack for the failures engineers see most often.
Built for: Engineers diagnosing broken API calls, browser errors, auth failures, or caching surprises.
What you should get from this path
- Diagnose CORS, auth, and server failures faster.
- Inspect live headers and cookies with better context.
- Move from symptoms to protocol-level root causes.
Start with targeted debug guides
Use the shortest path to the failure mode you are seeing.
- Debug Guide
Debugging CORS Errors
Step-by-step diagnosis for preflight failures, missing headers, and credentials issues.
CORS is one of the highest-friction browser errors and needs a dedicated checklist.
- Debug Guide
Debugging 403 Forbidden
Troubleshoot authz failures, CSRF, blocked IPs, and role checks.
Separates authentication problems from authorization and policy failures.
- Debug Guide
Debugging 500 Internal Server Error
Systematic workflow for server-side crashes, logs, and response handling.
Provides a disciplined production incident workflow rather than ad hoc guesses.
Inspect live behavior
Use tools that surface protocol details directly from real responses.
- Tool
Header Inspector
Fetch any URL and analyze response headers with linked guidance.
Makes missing headers, redirect chains, and cache policy issues visible immediately.
- Tool
CORS Debugger
Simulate requests and preflights to understand what the browser will allow.
Reduces the guesswork around origin, method, and credential combinations.
- Tool
Site Verifier
Scan a URL for TLS, security headers, cookies, and caching signals.
Bundles the most common production checks into one scan.
Keep these references nearby
These pages cover the response semantics and headers behind common failures.
- Status Code
HTTP 403 Forbidden: Access Denied
403 Forbidden means the server refuses the request. Find whether Cloudflare, nginx, Apache, S3 or your app sent it; fix permissions, WAF rules and role checks.
Explains the most common authorization failure code in detail.
- Status Code
HTTP 404 Not Found: What It Means and How to Fix It
404 Not Found means no resource exists at that URL. Find which layer sent it, then fix routing, deploys, rewrites, CDN cache and soft 404s, with curl checks.
Useful when debugging routes, rewrites, and stale client assumptions.
- Status Code
HTTP 500 Internal Server Error: Meaning and Fixes
500 means the server hit an error it did not handle. Find which layer sent it, read the right log for nginx, Apache, WordPress, Django, Next.js or Express.
Maps generic server failures to concrete debugging moves.
- Status Code
HTTP 429 Too Many Requests: Causes, Retry-After and Fixes
Fix HTTP 429 Too Many Requests: read Retry-After and RateLimit headers, back off with jitter, and set up express-rate-limit v7, nginx limit_req and Cloudflare.
Critical for diagnosing throttling and rate-limit behavior in production.
- Header
Access-Control-Allow-Origin Header: CORS Errors and Fixes
Access-Control-Allow-Origin explained: exact browser errors, why * fails with credentials, why you need Vary: Origin, and fixes for nginx, Express and Django.
Core reference when requests fail because the browser rejects the response.
- Header
Authorization Header: Bearer, Basic and 401 Fixes
Authorization header carries credentials as scheme plus token. Bearer and Basic formats, WWW-Authenticate, why proxies strip it, redirects, CORS and storage.
Relevant when request credentials are present but the server still rejects access.
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