HTTP status codes explained – 404, 500, 503 & more

In short

Every response from a web server begins with a three-digit code. The first digit tells you what is going on: 2xx = all good, 3xx = redirected, 4xx = error on your side (request, permissions, missing page), 5xx = error at the server. This page explains every important code, the most common cause on web hosting and the first step toward a fix.

How to read a status code

When your browser requests a page, the server first sends a status line such as HTTP/2 404. After that come headers and the content. You can see the code in your browser’s developer tools (F12 key, “Network” tab) or with curl:

curl -I https://meinprojekt.de/
curl -sI -o /dev/null -w "%{http_code}\n" https://meinprojekt.de/unterseite

The first command shows all headers, the second only the number.

Class	Meaning	Who is “to blame”?
1xx	Information, processing in progress	Nobody, rarely seen
2xx	Success	–
3xx	Redirect	A rule or plugin redirects
4xx	Error in the request	Wrong address, missing permissions, block
5xx	Error in the server	Script, configuration or load

What kind of code do you see?

3xx (redirect)Check where it redirects to→

403Access denied→

404Page not found→

500, 502, 503, 504Server error→

520 to 526Errors from Cloudflare→

1xx – Information

Code	Name	Meaning
100	Continue	The server has received the headers; the client should send the rest. Runs invisibly.
101	Switching Protocols	Switch of protocol, e.g. to WebSocket.
103	Early Hints	The server sends hints in advance about which files the page needs.

You do not have to do anything. Troubleshooting starts at 4xx and 5xx.

2xx – Success

Code	Name	Meaning
200	OK	The page was delivered. All good.
201	Created	Something was newly created, e.g. through an interface (API).
204	No Content	Successful, but without content.
206	Partial Content	Only part of the file, e.g. in video streaming.

200 and still broken

Some pages report “200 OK” but show an empty page or an error text. This is a “soft error”. In that case the fault lies in the script, not the server. Look in the error log (Error 500 and white page).

3xx – Redirects

A redirect sends the browser to a different address. This is intended for http to https or for moved pages, and unintended in loops.

Code	Name	Meaning	Permanent?	Method kept?
301	Moved Permanently	The page has moved. Search engines adopt the new address.	Yes	May become GET
302	Found	Temporarily elsewhere. Search engines keep the old address.	No	May become GET
303	See Other	After a form: fetch the target page with GET.	No	Becomes GET
304	Not Modified	The page has not changed; the browser uses its stored copy.	–	–
307	Temporary Redirect	Temporary; method and content stay the same.	No	Yes
308	Permanent Redirect	Permanent; method and content stay the same.	Yes	Yes

• 301 or 302? For “this page is moving for good” use 301, for “briefly under maintenance” use 302.
• 304 is not an error. It shows that caching works (Understanding caching).
• Too many redirects in a row produce “ERR_TOO_MANY_REDIRECTS” (redirect loop). See Error 404 and redirects.

4xx – Errors on the request side

The server understood the request but cannot or will not fulfil it.

Code	Name	Meaning	Common cause on web hosting	First step
400	Bad Request	The request is malformed.	Corrupt cookies, address too long, badly built request	Delete the site’s cookies, check the address
401	Unauthorized	Login required or wrong.	Password protection (.htpasswd) or wrong credentials	Check your credentials
403	Forbidden	Access forbidden.	Wrong file permissions, .htaccess block, security rule (WAF)	Error 403
404	Not Found	The address does not exist.	Typo, deleted page, missing permalink rules	Error 404
405	Method Not Allowed	Method (e.g. POST) not allowed.	Form submits to the wrong address, rule blocks it	Check the form’s target and method
406	Not Acceptable	The server cannot deliver the requested format.	Security rule blocks the request	Send the time and address to support
408	Request Timeout	The client was too slow.	Unstable connection	Reload, use another connection
409	Conflict	Conflict with the state of the data.	Simultaneous changes	Reload, try again
410	Gone	Page was removed on purpose.	Your own rule or plugin	Tells search engines: “page is gone for good”
413	Payload Too Large	Upload too large.	upload_max_filesize or post_max_size too small	Make the file smaller or adjust the PHP values in the web panel
414	URI Too Long	Address too long.	Very long parameters	Shorten the request
415	Unsupported Media Type	File type not allowed.	Upload of a blocked type	Choose another format
418	I’m a teapot	Joke code, rarely used.	–	–
421	Misdirected Request	Wrong server for this domain.	Domain not assigned to the website	Check the domain in the web panel
429	Too Many Requests	Too many requests in a short time.	Security or rate limiting, bots, plugin loop	Wait, find the trigger
431	Request Header Fields Too Large	Headers or cookies too large.	Too many or too large cookies	Delete cookies
451	Unavailable For Legal Reasons	Blocked for legal reasons.	Legal block	–

The most important 4xx codes in everyday use

• 404 is the most common. It is not a server outage, it just means “there is nothing at this address”.
• 403 has many possible sources: file permissions, .htaccess, a security rule. A 403 can also come from a security rule of the server that wrongly considers a request dangerous. In that case support can help: send them the time and the address.
• 429 limits automated queries. The cause is sometimes bots, sometimes your own services asking too often.

5xx – Errors in the server

Here your request is not wrong; something on the server or in your website is. On shared hosting, a look at the error log helps.

Code	Name	Meaning	Common cause on web hosting	First step
500	Internal Server Error	General error.	PHP error in the code, broken .htaccess, faulty plugin, memory limit	Error 500
501	Not Implemented	Function not available.	Unusual method	Rare, contact support
502	Bad Gateway	An upstream service returned nonsense.	PHP process crashed, redirect to a service	Reload, check plugins/scripts
503	Service Unavailable	Service currently unavailable.	Maintenance mode, overload, maintenance on the server	Wait briefly, look at the status page
504	Gateway Timeout	The service did not answer in time.	Very slow script, large import, slow database	Speed up the script, check the time limit
505	HTTP Version Not Supported	Protocol version not supported.	Outdated client	Rare
507	Insufficient Storage	No storage space.	Storage full	Free up space
508	Loop Detected	Loop detected.	Rewrite loop	Check .htaccess

500 or 503 – which is it?

500 means: something is broken (code, configuration). 503 means: the service is currently unable to respond (maintenance, overload). A 503 often disappears on its own, a 500 does not.

Cloudflare errors 520 to 526

The codes 520 to 526 do not exist in the HTTP standard. They come from Cloudflare, an intermediary service (CDN) that some websites use. You only see them if your domain runs through Cloudflare. They tell you at which point between Cloudflare and your server something goes wrong.

Code	Name	Meaning	What you can check
520	Web Server Returned an Unknown Error	Server responds unexpectedly.	Error log, PHP errors, redirect rules
521	Web Server Is Down	Server does not accept connections.	Is the website running? Status page, firewall
522	Connection Timed Out	Timeout while connecting.	Server overloaded or blocking Cloudflare addresses
523	Origin Is Unreachable	Server not reachable.	DNS in Cloudflare points to the wrong address
524	A Timeout Occurred	Server answered too late.	Slow script, long queries
525	SSL Handshake Failed	Encryption between Cloudflare and server fails.	Check the certificate on the server
526	Invalid SSL Certificate	Server certificate invalid.	Renew the certificate, check mode “Full” instead of “Full (strict)”

Cloudflare has several SSL modes. If the mode does not match the certificate on your server, 525/526 or redirect loops result. A valid certificate must exist on the server itself; more in SSL certificates and HTTPS.

How it all fits together

Where a status code originates

1. ▶Browser sends a requestGET /page
3. 2Optional: Cloudflare or another intermediary52x errors originate here
5. 3Web server (Apache)301/302/403/404, rules from .htaccess
7. 4PHP and database500/502/504 on script errors
9. ✓Response with status code

Checking status codes

# Just the code
curl -s -o /dev/null -w "%{http_code}\n" https://meinprojekt.de/

# Follow redirects and show every step
curl -sIL https://meinprojekt.de/ | grep -E "^HTTP|^location"

In the browser: F12, Network tab, reload the page, Status column.

Frequently asked questions

Is a 404 bad for search engines?

Individual 404 pages are normal. The problem is many important pages suddenly returning 404. Redirect moved pages with 301.

What should I send to support?

The address, the status code, the time and what you changed beforehand. More in Describing errors well.

Why is my 500 error gone after a minute?

Then it was usually a brief overload or a script that was just restarting. If it happens repeatedly, check the error log.

Further reading

• Error 500 and white page
• Error 403: access denied
• Error 404 and redirects
• Status page and maintenance