Error Encyclopedia

JSON Unexpected Token

Learn what causes the 'JSON Parse error: Unexpected token' error and how to fix it in JavaScript, Python, and other languages.

JSON Unexpected End of Input

Learn why 'Unexpected end of JSON input' occurs and how to fix truncated or incomplete JSON data.

JSON Circular Reference Error

Fix 'Converting circular structure to JSON' error when using JSON.stringify with objects that reference themselves.

401 Unauthorized Error

Learn what a 401 Unauthorized error means, common causes, and how to fix authentication failures in your web applications.

403 Forbidden Error

Learn what 403 Forbidden means, how it differs from 401, and how to fix access denied errors in your applications.

404 Not Found Error

Learn what 404 Not Found means, common causes, and how to fix broken links and missing resources on your website or API.

429 Too Many Requests Error

Learn what 429 Too Many Requests means, how rate limiting works, and how to handle or avoid hitting API rate limits.

500 Internal Server Error

Learn what 500 Internal Server Error means, common causes, and how to debug and fix server-side failures.

502 Bad Gateway Error

Learn what 502 Bad Gateway means, common causes like proxy or load balancer misconfiguration, and how to fix gateway errors.

503 Service Unavailable Error

Learn what 503 Service Unavailable means, how to fix maintenance mode and overload issues, and how to implement proper downtime handling.

CORS Policy Blocked Request

Learn how to fix 'CORS policy: No Access-Control-Allow-Origin header' errors. Understand how CORS works and how to configure it correctly.

CORS Preflight Request Failed

Fix CORS preflight (OPTIONS) request failures. Learn how browsers check CORS permissions before making cross-origin requests.

Module Not Found Error

Fix 'Cannot find module' and 'Module not found' errors in Node.js, TypeScript, and bundlers. Learn how to resolve import path issues.

TypeScript Type Not Assignable Error

Fix 'Type X is not assignable to type Y' errors in TypeScript. Learn how to debug type mismatches, use proper typing, and leverage type inference.

400 Bad Request Error

Learn what 400 Bad Request means, common causes like malformed syntax or invalid request parameters, and how to fix them.

408 Request Timeout Error

Learn what 408 Request Timeout means, why servers time out idle connections, and how to fix slow request issues.

413 Payload Too Large Error

Fix 413 Payload Too Large errors when uploading files or sending large request bodies.

422 Unprocessable Entity Error

Learn what 422 Unprocessable Entity means for API validation errors, how it differs from 400, and how to fix validation failures.

504 Gateway Timeout Error

Fix 504 Gateway Timeout errors. Learn how proxies, load balancers, and CDNs time out waiting for upstream servers.

Invalid Content-Type Header Error

Fix 'Invalid Content-Type' errors when the request Content-Type header does not match the request body format.

ENOENT: File Not Found Error

Fix 'ENOENT: no such file or directory' errors in Node.js. Learn how to check file paths, handle missing files gracefully, and debug file system operations.

EACCES: Permission Denied Error

Fix 'EACCES: permission denied' errors in Node.js and Linux. Learn how to fix file permission, port binding, and npm global install issues.

EADDRINUSE: Port Already in Use Error

Fix 'EADDRINUSE: address already in use' errors. Learn how to find and kill processes using a port, or configure port fallbacks.

Socket Hang Up Error

Fix 'socket hang up' errors in Node.js HTTP clients. Learn why connections are terminated prematurely and how to handle them.

Maximum Call Stack Size Exceeded Error

Fix 'Maximum call stack size exceeded' errors caused by infinite recursion or deep object traversal in JavaScript.

JavaScript Heap Out of Memory Error

Fix 'JavaScript heap out of memory' errors in Node.js. Learn to increase memory limits, detect memory leaks, and optimize memory usage.

Objects Not Valid as a React Child Error

Fix 'Objects are not valid as a React child' error. Learn how React renders content and why objects cannot be directly rendered.

React Missing Key Prop Warning

Fix 'Each child in a list should have a unique key' warning in React. Learn why keys are important and how to choose good key values.

Cannot Read Properties of Undefined Error

Fix 'Cannot read properties of undefined (reading map)' and similar errors in React. Learn how to handle async data and null checks.

React Too Many Re-renders Error

Fix 'Too many re-renders' error in React. Learn how state updates cause infinite loops and how to use useEffect correctly.

React Invalid Hook Call Error

Fix 'Invalid hook call' error in React. Learn the rules of hooks — only call hooks at the top level and only from React function components.

Next.js Image Optimization Error

Fix common Next.js Image Optimization errors including invalid src, missing domains config, and sharp installation issues.

Duplicate Key Constraint Violation Error

Fix 'duplicate key value violates unique constraint' errors in PostgreSQL, MySQL, and other databases when inserting duplicate data.

Column Does Not Exist Error

Fix 'column does not exist' SQL errors in PostgreSQL, MySQL, and other databases when querying or migrating schemas.

Database Deadlock Detected Error

Fix 'deadlock detected' errors in PostgreSQL and other databases. Learn why concurrent transactions deadlock and how to prevent them.

Database Connection Pool Exhausted Error

Fix 'connection pool exhausted' or 'too many connections' errors in PostgreSQL, MySQL, and other databases.

npm ERR! code E401 — Unauthorized Error

Fix 'npm ERR! code E401' errors when installing or publishing private packages. Learn how to authenticate with npm registries.

Command Not Found Error

Fix 'command not found' errors in terminal and CLI. Learn how to fix PATH issues, install missing tools, and use npx for Node.js packages.

SSH Permission Denied (publickey) Error

Fix 'Permission denied (publickey)' SSH errors when connecting to GitHub, AWS, or remote servers.

fatal: Not a Git Repository Error

Fix 'fatal: not a git repository' errors when running git commands outside a git repository or in a detached work tree.

npm ERR! code E403 — Forbidden Error

Fix 'npm ERR! code E403' errors when publishing packages, accessing restricted packages, or hitting npm registry permissions.

OAuth Invalid Grant Error

Fix 'invalid_grant' OAuth 2.0 errors when exchanging authorization codes or refreshing tokens.

JWT Malformed Error

Fix 'jwt malformed' errors when decoding or verifying JWT tokens. Learn the correct JWT format and how to debug invalid tokens.

JWT Token Expired Error

Fix 'jwt expired' errors. Learn how JWT expiration works, how to check the exp claim, and implement token refresh flows.

JWT Invalid Signature Error

Fix 'invalid signature' JWT errors. Learn how JWT signatures work, why they fail, and how to use the correct secret key.

SSL Certificate Expired Error

Fix 'NET::ERR_CERT_DATE_INVALID' and 'SSL certificate expired' errors in browsers. Learn how to update and manage SSL/TLS certificates.

DNS Not Resolved Error

Fix 'DNS not resolved' or 'net::ERR_NAME_NOT_RESOLVED' errors. Learn how DNS resolution works and how to fix domain name lookup failures.

Connection Refused Error

Fix 'ECONNREFUSED' and 'Connection refused' errors when connecting to databases, APIs, or other services.

ERR_CONNECTION_RESET Error

Fix 'ERR_CONNECTION_RESET' or 'net::ERR_CONNECTION_RESET' errors in Chrome and other browsers. Learn why TCP connections are reset and how to fix them.

ERR_SSL_PROTOCOL_ERROR Error

Fix 'ERR_SSL_PROTOCOL_ERROR' errors in Chrome and browsers. Learn how SSL/TLS handshake failures happen and how to fix protocol mismatches.

Git Merge Conflict

Learn how to resolve git merge conflicts. Understand conflict markers, use merge tools, and prevent conflicts in collaborative development.

Detached HEAD State

Fix detached HEAD state in Git. Learn what it means, how to avoid losing work, and how to reattach your HEAD to a branch.

ModuleNotFoundError: No module named

Fix 'ModuleNotFoundError: No module named' errors in Python. Learn to install missing packages, fix import paths, and manage virtual environments.

IndentationError: unexpected indent

Fix 'IndentationError: unexpected indent' in Python. Learn Python's indentation rules and how to fix spacing issues.

KeyError

Fix Python KeyError when accessing dictionary keys that do not exist. Learn to use .get(), setdefault(), and try-except safely.

TS2304: Cannot find name

Fix TypeScript error TS2304 'Cannot find name'. Learn how to declare types, install type definitions, and configure tsconfig.json properly.

TS2339: Property does not exist on type

Fix TypeScript error TS2339 'Property does not exist on type'. Learn to type objects correctly, use type assertions, and narrow types with guards.

TS18048: 'x' is possibly 'undefined'

Fix TypeScript error TS18048 'is possibly undefined'. Learn to use optional chaining, nullish coalescing, and strict null checks correctly.

Cannot Connect to Docker Daemon

Fix 'Cannot connect to the Docker daemon' error. Learn how to start Docker Desktop, check daemon status, and resolve permission issues.

Port is Already Allocated (Docker)

Fix 'port is already allocated' Docker error when ports conflict between containers or host processes.