Error map
428 HTTP 428 Precondition Required
HTTP · layer 2, Network
Centre: this error. First ring: errors it is linked with (12). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (12)
java.util.concurrent.TimeoutException
A Future.get(timeout) or async operation didn’t complete in the allowed time.
HTTP 304 Not Modified
The cached copy is still valid, so the server sends no body and the client reuses its cache.
Unexpected characters at the top of the page / headers already sent by BOM
A UTF-8 byte-order mark (BOM) at the start of a PHP file is sent as output, breaking headers, JSON and images.
HTTP 100 Continue
An interim response telling the client to go ahead and send the request body — normal when the client sent Expect: 100-continue.
Cloudflare Error 1040 / 1041: Invalid request header modification
A Transform Rule tried to set or remove a request header that Cloudflare doesn’t allow to be modified, or produced an invalid val…
Go: fatal error: all goroutines are asleep - deadlock!
Every goroutine is blocked waiting (on a channel, mutex or WaitGroup), so the program can never continue.
Refused to load the script because it violates the following Content Security Policy directive
The page’s Content-Security-Policy doesn’t allow that script, style, image or connection source.
Optimistic lock conflict: OptimisticLockException / StaleObjectStateException / version mismatch
Someone else changed the record after you read it, so your update — based on an old version — was rejected to avoid overwriting t…
HTTP 103 Early Hints
An interim response that sends Link headers early so the browser can preload CSS, fonts or scripts while the server is still buil…
HTTP 417 Expectation Failed
The server or a proxy can’t meet the Expect header in the request — almost always Expect: 100-continue.
EF Core: A second operation was started on this context instance before a previous operation completed
The same DbContext was used concurrently — async calls not awaited, parallel tasks sharing a context, or a context registered as…
Main Thread Checker: UI API called on a background thread: -[UIView setNeedsLayout]
UIKit was used from a background thread; UI must only be touched on the main thread.
Two steps away (36)
HTTP 408 Request Timeout
The server closed the connection because the client took too long to send the complete request.
HTTP 504 Gateway Timeout
A proxy or gateway waited too long for the upstream server to respond and gave up.
HTTP 409 Conflict
The request conflicts with the current state of the resource — e.g. a duplicate or an edit based on an outdated version.
HTTP 301 Moved Permanently
The resource has a new permanent URL; clients and search engines should use the address in the Location header from now on.
HTTP 412 Precondition Failed
A conditional request header (If-Match, If-Unmodified-Since) didn’t match the current state of the resource.
HTTP 200 OK (but something is still wrong)
The request succeeded at the HTTP level — yet the page is blank, the data is wrong, or an error is hidden inside the response bod…
Warning: Cannot modify header information - headers already sent
You called `header()`, `setcookie()` or `session_start()` after output had already been sent to the browser.
CORS Error: No 'Access-Control-Allow-Origin' header is present
The browser blocked a cross-origin request because the server’s response didn’t include the CORS headers allowing your site’s ori…
HTTP 411 Length Required
The server refuses a request with a body but no Content-Length header.
HTTP 413 Content Too Large (Request Entity Too Large)
The request body is bigger than the server is willing to accept — usually a file upload over the configured limit.
HTTP 505 HTTP Version Not Supported
The server doesn’t support the HTTP protocol version used in the request.
WordPress: The link you followed has expired
Usually an upload (theme, plugin, media) larger than PHP’s upload/post limits — WordPress receives an empty request and shows thi…
Warning: session_start(): Session cannot be started after headers have already been sent
session_start() ran after output was sent, so PHP can’t set the session cookie.
HTTP 416 Range Not Satisfiable
The client asked for a byte range (Range: bytes=…) that lies outside the file — usually a resumed download of a file that changed…
Cloudflare Error 1035 / 1036: Invalid request rewrite (invalid URI path / query string)
A Transform Rule (URL rewrite) produced an invalid path or query string.
java.util.ConcurrentModificationException
A collection was modified while being iterated (even in a single thread).
java.lang.InterruptedException (sleep interrupted)
A blocked thread (sleep, wait, join, queue take) was interrupted by another thread.
ERROR: could not serialize access due to concurrent update
A REPEATABLE READ/SERIALIZABLE transaction conflicted with a concurrent one and must be retried.
Mixed Content: The page was loaded over HTTPS, but requested an insecure resource
An HTTPS page tried to load a script, API or image over plain HTTP, and the browser blocked (or warned about) it.
SecurityError: Blocked a frame with origin "x" from accessing a cross-origin frame.
Script tried to read or modify an iframe (or window) from another origin.
Script error. (at line 0) — cross-origin error details hidden
An error happened in a script from another origin, and the browser hid the details.
Error: Too many re-renders. React limits the number of renders to prevent an infinite loop.
A state update runs during render, which triggers another render, which updates state again — forever.
Warning: A component is changing an uncontrolled input to be controlled
An input’s `value` started as `undefined` (uncontrolled) and later became a defined value (controlled), or vice versa.
java.lang.IllegalStateException
A method was called when the object wasn’t in the right state for it.
Cloudflare Error 524: A Timeout Occurred
Cloudflare connected to the origin, but the origin didn’t send an HTTP response within 100 seconds.
ERROR: canceling statement due to statement timeout
A query ran longer than statement_timeout and PostgreSQL cancelled it.
Performance: N+1 query problem (one query per row in a loop)
Code runs one query to load a list, then one more query per item — hundreds of queries per page.
HTTP 400 Bad Request
The server could not understand the request because its syntax, headers or body are malformed or invalid.
HTTP 407 Proxy Authentication Required
A proxy between you and the server requires credentials before it will forward your request.
Upload error: File type not allowed / unsupported file type
The upload was rejected because the file’s type — extension, MIME type or actual content — isn’t on the allowed list.
InvalidOperationException: Unable to resolve service for type 'X' while attempting to activate 'Y'
ASP.NET Core’s dependency injection container can’t build Y because one of its constructor dependencies (X) was never registered.
API Error: Idempotency key reused with different parameters (idempotency_key_in_use)
An Idempotency-Key header was sent again with a different request body, or while the first request with that key was still runnin…
API Error: Too many concurrent requests (concurrency limit reached)
You have more requests in flight at once than the API allows for your key — even if your requests-per-minute rate is fine.
ConditionalCheckFailedException: The conditional request failed
A write’s ConditionExpression evaluated to false, so DynamoDB didn’t perform it — often exactly as designed.
Operation cannot be fulfilled on deployments.apps "x": the object has been modified; please apply your changes to the latest version and try again
Optimistic-concurrency conflict: the object changed (new resourceVersion) between when you read it and when you tried to update i…
Conflict: AnotherOperationInProgress — Another operation is in progress on the resource
Azure is still processing a previous change on the same resource, so new operations are rejected until it finishes.
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