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See all trending →HTTP 400 Bad Request
The server could not understand the request because its syntax, headers or body are malformed or invalid.
HTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
Firestore: FirebaseError: [code=permission-denied]: Missing or insufficient permissions
Firestore Security Rules denied the read/write — the user isn’t signed in, the rule conditions don’t match, or test-mode rules ex…
HTTP 403 Forbidden
The server understood the request but refuses to authorize it — you (or the server process) are not allowed to access this resour…
Redis: (error) LOADING Redis is loading the dataset in memory
Redis is starting and still reading its RDB/AOF, so it rejects commands temporarily.
Python requests: HTTPSConnectionPool(host='api.example.com', port=443): Max retries exceeded with url: /v1 (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] ...')))
The `requests` call failed during the TLS step and exhausted its retries; the real reason is in the nested SSLError text.
Compute Engine: ERROR: (gcloud.compute.instances.create) Could not fetch resource: The resource 'projects/p/zones/z/instances/vm-1' already exists
You tried to create a resource whose name is already taken in that scope.
Cloud Storage: 403 Forbidden — user@example.com does not have storage.objects.get access to the Google Cloud Storage object
The identity making the request has no read permission on that bucket or object.
Secret Manager: 7 PERMISSION_DENIED: Permission 'secretmanager.versions.access' denied for resource 'projects/123/secrets/db-pass/versions/latest'
The calling identity lacks the Secret Accessor role on that secret, or the secret/version does not exist.
Laravel: Illuminate\Auth\Access\AuthorizationException: This action is unauthorized.
A policy or gate denied the action for the current user, so Laravel returned HTTP 403.
Laravel: Symfony\Component\Mailer\Exception\TransportException: Connection could not be established with host "smtp.mailtrap.io:2525": stream_socket_client(): Unable to connect
Laravel's mailer could not connect to the SMTP host configured in `.env`.
HTTP 404 Not Found
The server can’t find anything at the requested URL.
[nodemon] app crashed - waiting for file changes before starting...
Your app threw an error on startup; nodemon is waiting for a file change to retry.
Thread 1: signal SIGABRT (app crashes with "libc++abi: terminating")
The app deliberately aborted — an uncaught exception, failed assertion or fatalError. The console above the crash has the real me…
Jenkins: Still waiting to schedule task — Waiting for next available executor / 'agent1' is offline
A Jenkins build is queued because no executor with the required label is free or the agent is offline.
ERROR: prepared statement "s1" already exists (PgBouncer transaction mode)
Named prepared statements collided — typically because PgBouncer in transaction pooling mode hands connections between clients.
System has not been booted with systemd as init system (PID 1). Can't operate.
You ran systemctl inside an environment without systemd as PID 1 — a Docker container or older WSL.
Flutter: Unhandled Exception: SocketException: Failed host lookup: 'api.example.com' (OS Error: No address associated with hostname, errno = 7)
The app could not resolve or reach the server: no internet, wrong host name, DNS failure, or missing network permission.
Most looked-up errors
2,380 errors documentedHTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
HTTP 403 Forbidden
The server understood the request but refuses to authorize it — you (or the server process) are not allowed to access this resour…
HTTP 400 Bad Request
The server could not understand the request because its syntax, headers or body are malformed or invalid.
ORA-00933: SQL command not properly ended
Oracle found extra clauses or syntax it doesn’t support at the end of a statement.
MySQL ERROR 1064 (42000): You have an error in your SQL syntax
MySQL couldn’t parse the query. The text after “near” shows where parsing failed.
WordPress: There Has Been a Critical Error on This Website
A PHP fatal error (usually from a plugin or theme) stopped WordPress; the real error is in the debug log or recovery-mode email.
Could not load file or assembly 'X, Version=…' or one of its dependencies
The runtime couldn’t find or load a referenced DLL — missing from the output, wrong version, or wrong platform (x86/x64).
TypeError: Cannot read properties of undefined (reading 'x')
You tried to access a property on a value that is `undefined` (or `null`) — usually data that hasn’t loaded yet or a wrong proper…
Thread 1: signal SIGABRT (app crashes with "libc++abi: terminating")
The app deliberately aborted — an uncaught exception, failed assertion or fatalError. The console above the crash has the real me…
The application was unable to start correctly (0xc000007b)
A program loaded a DLL of the wrong architecture (32-bit vs 64-bit) or a corrupted runtime library.
Warning: Undefined array key / Undefined index
Your code reads an array key that doesn’t exist — common with `$_GET`, `$_POST` and decoded JSON.
HTTP 404 Not Found
The server can’t find anything at the requested URL.
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Paste a raw error, log line, HTTP response or stack trace. We detect the error code, platform and request, match it against our knowledge base, and tell you the likely cause and what to check first.
403 Forbidden nginx/1.24.0 GET /api/usersAnalyze an error
⚖️ Confusing pairs, explained
- 301 vs 302: Permanent vs Temporary Redirect
- 401 vs 403: Unauthorized vs Forbidden
- 400 vs 422: Bad Request vs Unprocessable Content
- Cloudflare 525 vs 526: SSL Handshake Failed vs Invalid SSL Certificate
- Authentication vs Authorization
- 406 vs 415: Not Acceptable vs Unsupported Media Type