What Are HTTP Status Codes and What Do They Mean? (200, 404, 500 Explained)
Every time you make an API call or visit a website, the server responds with more than just data – it sends back a three-digit status code that tells you exactly what happened with your request. These codes are like the server’s way of saying “Success!”, “You made a mistake,” or “Something’s broken on my end.”
Understanding HTTP status codes is crucial for debugging API issues, building robust applications, and creating better user experiences. When your app breaks, these codes are often your first clue about what went wrong and where to look for solutions.
Brief History: Why Status Codes Exist
Section titled “Brief History: Why Status Codes Exist”HTTP status codes were designed in the early 1990s as a standardized way for servers to communicate request outcomes. Rather than forcing developers to parse response messages in different languages, status codes provide a universal numeric language that every HTTP client can understand instantly. The three-digit format allows for logical grouping while leaving room for future expansion.
Status Code Categories
Section titled “Status Code Categories”HTTP status codes follow a logical pattern where the first digit indicates the category:
2xx (200-299): Success These status codes indicate that the client’s request was successfully received, understood, and accepted.
Examples: 200 OK, 201 Created, 202 Accepted
3xx (300-399): Redirection These status codes indicate that further action needs to be taken by the client to complete the request.
Examples: 301 Moved, 302 Found
4xx (400-499): Client Error These status codes indicate that the client seems to have made an error in their request.
Examples: 404 Not Found, 409 Conflict, 422 Validation
5xx (500-599): Server Error These status codes indicate that the server failed to fulfill a valid request from the client.
Examples: 500 Internal Error, 502 Bad Gateway, 503 Unavailable
Restaurant Service Analogy
Section titled “Restaurant Service Analogy”Think of status codes like responses from a restaurant’s order system:
- 2xx: “Your order is ready!” (Success) ✔️
- 3xx: “We moved to a new location, go to…” (Redirection) 🏃♂️
- 4xx: “You ordered something not on the menu” (Your mistake) 🚨
- 5xx: “Our kitchen is broken” (Restaurant’s problem) 🥲
2xx Success Codes
Section titled “2xx Success Codes”200 OK - Standard Success
Section titled “200 OK - Standard Success”When Used: Request succeeded and server is returning requested data.
Client Handling: Process the returned data normally.
API Design: Use for successful GET, PUT, PATCH requests that return data.
201 Created - Resource Created
Section titled “201 Created - Resource Created”When Used: New resource was successfully created (typically POST requests).
Client Handling: Extract new resource ID from response or Location header.
API Design: Always use for successful resource creation, include Location header.
202 Accepted - Request Queued for Processing
Section titled “202 Accepted - Request Queued for Processing”When Used: Server accepted the request for processing but hasn’t completed it yet.
Client Handling: Poll the status URL or wait for webhook notification to check completion.
API Design: Use for long-running operations, always provide way to check status.
204 No Content - Success Without Data
Section titled “204 No Content - Success Without Data”When Used: Request succeeded but there’s no content to return (often DELETE requests).
Client Handling: Request succeeded, no response data to process.
API Design: Use for successful DELETE operations or updates that don’t return data.
3xx Redirection Codes
Section titled “3xx Redirection Codes”301 Moved Permanently - Resource Moved
Section titled “301 Moved Permanently - Resource Moved”When Used: Resource has permanently moved to a new URL.
Client Handling: Update bookmarks/links to use new URL.
API Design: Use when permanently changing endpoint URLs, always include Location header.
302 Found - Temporary Redirect
Section titled “302 Found - Temporary Redirect”When Used: Resource temporarily available at different URL.
Client Handling: Follow redirect but keep using original URL for future requests.
API Design: Use for temporary relocations or load balancing redirects.
4xx Client Error Codes
Section titled “4xx Client Error Codes”400 Bad Request - Invalid Request
Section titled “400 Bad Request - Invalid Request”When Used: Request syntax is malformed or invalid parameters.
Debugging: Check request format, required fields, parameter types.
Client Handling: Show user-friendly error, validate input before sending.
API Design: Provide specific error details about what’s wrong.
401 Unauthorized - Authentication Required
Section titled “401 Unauthorized - Authentication Required”When Used: Request lacks valid authentication credentials.
Debugging: Check if API key/token is included and valid.
Client Handling: Redirect to login or prompt for credentials.
API Design: Include WWW-Authenticate header with auth method.
403 Forbidden - Access Denied
Section titled “403 Forbidden - Access Denied”When Used: Server understood request but refuses to authorize it. This includes both permission denial and resource quota exhaustion.
Debugging:
- User is authenticated but lacks permission for this action
- User has exhausted their API quota (monthly/daily limit)
- Check if quota is exhausted via
X-Quota-*headers
Client Handling:
- Show “access denied” or “quota exceeded” message based on response
- For quota errors: direct user to upgrade page or show reset time
- Don’t retry automatically
API Design: Clearly explain why access was denied (permissions vs quota exhaustion).
404 Not Found - Resource Doesn’t Exist
Section titled “404 Not Found - Resource Doesn’t Exist”When Used: Requested resource doesn’t exist on the server.
Debugging: Check URL spelling, verify resource ID exists.
Client Handling: Show “not found” message, offer alternative actions.
API Design: Use for missing resources, not for access control.
Exception: Some servers use 404 as a generic response when they don’t want to reveal the specific reason for denying access (security through obscurity). However, this practice can make debugging harder and is generally discouraged in favor of more specific 4xx codes.
422 Unprocessable Entity - Validation Failed
Section titled “422 Unprocessable Entity - Validation Failed”When Used: Request is syntactically correct but semantically invalid.
Debugging: Request format is correct but data doesn’t meet business rules.
Client Handling: Show field-specific validation errors to user.
API Design: Provide detailed field-level error information.
429 Too Many Requests - Rate Limited
Section titled “429 Too Many Requests - Rate Limited”When Used: Client is making requests too quickly and has exceeded the per-minute rate limit.
Debugging: Slow down request frequency or implement retry logic with exponential backoff.
Client Handling: Respect Retry-After header, implement exponential backoff, add delays between requests.
API Design: Include Retry-After header with wait time.
Note: This is different from quota exhaustion (403). Rate limits are per-minute restrictions, while quotas (403) are daily/monthly allocations.
403 vs 429: Quota vs Rate Limiting
Section titled “403 vs 429: Quota vs Rate Limiting”403 Forbidden (Quota Exhausted)
- You’ve used up your monthly/daily quota allocation
- Non-temporary - wait for quota reset or upgrade plan
- Example: Used 10,000/10,000 monthly requests
- Response includes link to upgrade page
429 Too Many Requests (Rate Limited)
- You’re making requests too quickly
- Temporary - slow down and retry with delays
- Example: 201 requests in 1 minute (limit: 200/min)
- Implement exponential backoff retry logic
5xx Server Error Codes
Section titled “5xx Server Error Codes”500 Internal Server Error - Something’s Broken
Section titled “500 Internal Server Error - Something’s Broken”When Used: Server encountered unexpected error it can’t handle.
Debugging: Check server logs, this is a server-side issue.
Client Handling: Retry after delay, show generic error message.
API Design: Log detailed errors server-side, return generic message to client.
502 Bad Gateway - Upstream Server Error
Section titled “502 Bad Gateway - Upstream Server Error”When Used: Server acting as gateway received invalid response from upstream server.
Debugging: Problem with load balancer, proxy, or upstream service.
Client Handling: Retry after delay, likely temporary issue.
503 Service Unavailable - Server Temporarily Down
Section titled “503 Service Unavailable - Server Temporarily Down”When Used: Server temporarily unable to handle requests (maintenance, overload).
Debugging: Server is intentionally offline or overloaded.
Client Handling: Respect Retry-After header, show maintenance message.
API Design: Use during planned maintenance, include Retry-After header.
520 Web Server Error - Cloudflare Specific
Section titled “520 Web Server Error - Cloudflare Specific”When Used: Cloudflare received invalid or unexpected response from origin server.
Debugging: Issue between Cloudflare and your origin server.
Client Handling: Retry after delay, contact site administrator if persistent.
Note: This is a Cloudflare-specific code, not part of official HTTP standards.
Status Code Best Practices
Section titled “Status Code Best Practices”For API Developers
Section titled “For API Developers”-
Be Specific: Use the most accurate status code for each situation
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Consistency: Use the same codes for similar situations across your API
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Include Error Details: Always provide helpful error messages in response body
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Don’t Abuse 200: Don’t return 200 OK for error conditions with error details in body
For API Consumers
Section titled “For API Consumers”-
Handle Categories: Write code that handles 2xx, 4xx, and 5xx categories appropriately
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Respect Rate Limits: Honor 429 responses and Retry-After headers
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Retry Logic: Implement smart retries for 5xx errors but not 4xx errors
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User Experience: Translate status codes into meaningful messages for users
Debugging with Status Codes
Section titled “Debugging with Status Codes”Quick Debugging Guide
Section titled “Quick Debugging Guide”- 2xx codes: Request succeeded, process response
- 3xx codes: Follow redirects automatically (most HTTP clients do this)
- 4xx codes: Fix your request (check authentication, parameters, permissions)
- 5xx codes: Server problem, try again later or contact support
Common Status Code Mistakes
Section titled “Common Status Code Mistakes”Using Wrong Codes
Section titled “Using Wrong Codes”❌ Wrong: Returning 200 OK with error message in body
⚠️ Why it is wrong: This is confusing to clients as the status code contradicts the response body. Applications expect success for 200 codes, so error handling may be bypassed, creating subtle bugs.
✅ Right: Return appropriate 4xx or 5xx code with error details
Inconsistent Usage
Section titled “Inconsistent Usage”❌ Wrong: Using 404 for missing resources and access denial
⚠️ Why it is wrong: Inconsistent status codes make debugging difficult and confuse users. Clients can’t reliably determine if a resource doesn’t exist or if they lack permission to access it.
✅ Right: Use 404 for missing resources, 403 for access denial
Missing Error Details
Section titled “Missing Error Details”❌ Wrong: Just returning status code without explanation
⚠️ Why it is wrong: Without detailed error messages, developers waste time guessing what went wrong. Good error responses should explain the issue and suggest how to fix it.
✅ Right: Include helpful error message and recovery suggestions
Official Resources
Section titled “Official Resources”For comprehensive status code information, consult these authoritative sources:
- RFC 7231 - HTTP/1.1 Semantics: Official HTTP specification
- MDN HTTP Status Codes: Developer-friendly documentation
- IANA Status Code Registry: Complete official registry
The Bottom Line
Section titled “The Bottom Line”HTTP status codes are a universal language for communicating request outcomes between clients and servers. They provide immediate insight into what happened with your request and guide you toward the appropriate response – whether that’s processing successful data, fixing a malformed request, or implementing retry logic for server errors.
Understanding these codes helps you build more robust applications, debug issues faster, and create better user experiences. When something goes wrong with an API call, the status code is usually your first and most important clue about what happened and how to fix it.
Master these numeric messages, and you’ll be fluent in the fundamental feedback system that keeps the web’s communication flowing smoothly.
Continue Your API Journey
Section titled “Continue Your API Journey”Ready to dive deeper?
- What is an Endpoint? API Endpoints Explained - Learn about API endpoints, their key components, common patterns and endpoint design best practices.
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What’s the difference between 401 and 403?
401 Unauthorized means you need to authenticate (missing or invalid credentials). 403 Forbidden means you’re authenticated but don’t have permission to access this resource.
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Should I use 200 for all successful responses?
No. Use 200 for successful GET requests, 201 for resource creation, 204 for successful deletion without response body, and 202 for accepted async operations.
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What status code should I return for validation errors?
Use 422 Unprocessable Entity for semantic validation errors (invalid email format, missing required field). Use 400 Bad Request for malformed syntax.
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When should I use 500 vs 503?
Use 500 Internal Server Error for unexpected application errors. Use 503 Service Unavailable for planned maintenance or temporary outages (includes Retry-After header).
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Is 404 only for missing pages?
No. Use 404 for any resource not found: missing user IDs, deleted articles, non-existent endpoints. It means “the requested resource does not exist.”