Error Reference

Blocked by CORS policy The browser blocked a request because the server it called did not say your site is allow… Mixed Content Your page is HTTPS but it tried to load something over plain HTTP, so the browser blocked… ERR_CONNECTION_REFUSED Nothing is listening at the address/port you tried to reach, so the connection was refuse… Refused by Content Security Policy A Content-Security-Policy header blocked a script, style, image, or connection that isn't… ERR_TOO_MANY_REDIRECTS The page kept redirecting in a loop until the browser gave up. ERR_BLOCKED_BY_CLIENT A browser extension (usually an ad/tracker blocker) blocked the request — not the server.

400 Bad Request The server couldn't understand the request because it's malformed. 401 Unauthorized You aren't authenticated — the server doesn't know who you are. 403 Forbidden The server knows who you are but won't let you do this. 404 Not Found The server is up, but there's nothing at the URL you requested. 405 Method Not Allowed The URL exists, but not for the HTTP method you used (GET/POST/PUT/…). 429 Too Many Requests You've sent too many requests in a short time and hit a rate limit. 500 Internal Server Error The server hit an unhandled error while processing the request — the real cause is in its… 502 Bad Gateway A proxy/load-balancer got an invalid (or no) response from the upstream app server. 503 Service Unavailable The server is temporarily unable to handle the request — overloaded, down, or in maintena… 504 Gateway Timeout A proxy waited for the upstream server but it didn't respond in time.

Cannot read properties of undefined / null You tried to read a property off a value that was undefined or null — the thing you expec… X is not a function You called something as a function, but it isn't one. X is not defined (ReferenceError) You used a name that doesn't exist in scope. Unexpected token (SyntaxError) The JavaScript (or JSON) parser hit a character it didn't expect — usually a typo in the … Unexpected end of JSON input JSON.parse got an empty or truncated string — there was nothing (or not enough) to parse. Maximum call stack size exceeded A function called itself (directly or indirectly) without a stopping condition — infinite… Cannot use import statement outside a module You used ES module import in a context that isn't treated as a module. Hydration failed (React / Next.js) The HTML the server rendered didn't match what React produced on the client.

Access denied for user (MySQL 1045) MySQL rejected the login — the user, password, or host isn't accepted. SQL syntax error (1064) The database couldn't parse your SQL — there's a syntax mistake at the spot it names. Table doesn't exist (1146) The query references a table the database can't find. Duplicate entry / unique violation (1062) You tried to insert/update a row that collides with a UNIQUE or PRIMARY key. Foreign key constraint fails (1452) A row references a parent row that doesn't exist (or you're deleting a parent that still … Unknown column (1054) The query names a column that doesn't exist in that table. Can't connect to MySQL (2002) The client couldn't reach the MySQL server at all. Deadlock found Two transactions each held a lock the other needed, so the database killed one to break t…

Call to undefined function (PHP) PHP tried to call a function that doesn't exist at that point. Parse error: syntax error (PHP) PHP couldn't even compile the file — there's a syntax mistake, usually just before the li… Allowed memory size exhausted (PHP) The script tried to use more memory than PHP allows and was killed. Maximum execution time exceeded (PHP) The script ran longer than max_execution_time and PHP stopped it. Headers already sent (PHP) Something already sent output to the browser, so PHP can't set headers/cookies/redirects … Call to a member function on null (PHP) You called a method on a variable that was null — the object you expected wasn't created. Undefined variable / array key (PHP) You read a variable or array key that was never set. Too few arguments to function (PHP) You called a function/method without all of its required parameters.

Permission denied The user/process doesn't have permission to read, write, or execute that file or resource. No such file or directory The path you referenced doesn't exist (at least not from where the process is running). command not found The shell couldn't find that command — it isn't installed or isn't on PATH. Address already in use (EADDRINUSE) The port you tried to bind is already taken by another process. Connection refused (ECONNREFUSED) Nothing accepted the connection at that host/port — the service isn't listening there. Segmentation fault (core dumped) A program crashed by accessing memory it shouldn't — a bug in the binary or a bad library. No space left on device (ENOSPC) The disk (or the inode table) is full, so the write failed. Killed / exit code 137 (Out of memory) The process was killed — exit 137 means SIGKILL, usually the out-of-memory killer or a co…

Certificate expired / date invalid The site's TLS certificate is outside its valid date range (usually expired). Certificate authority invalid / self-signed The browser/client doesn't trust the certificate's issuer — it's self-signed or the chain… Certificate hostname mismatch The certificate is valid but isn't issued for the hostname you're visiting. SSL handshake / protocol error The client and server couldn't agree on a secure connection. NXDOMAIN / name not resolved DNS couldn't find that domain — there's no record for the name. DNS server failure / SERVFAIL The DNS resolver itself failed to answer (not a missing record — a resolver problem).