150 Free Developer Tools — Code Checkers, Formatters & More

Free online developer tools: code quality and complexity checkers, security scanners, JSON/SQL/XML formatters, hash and JWT tools, converters and fintech validators. Private and browser-based.

Formatting

JSON Formatter & Validator — Beautify, minify, and validate JSON with readable syntax errors.
SQL Formatter — Format and minify SQL with readable keywords and indentation.
Code Formatter — Format JavaScript, TypeScript, JSON, CSS, HTML, and Markdown with Prettier.
JSON Viewer — View JSON as a tree or as a list of JSON paths with the type of every value.
XML Formatter — Format and indent XML with 2 spaces, 4 spaces or tabs, after checking it is well-formed.
XML Minifier — Minify XML by removing comments and whitespace between tags.
HTML Beautifier — Beautify and indent HTML with Prettier, including inline CSS and JavaScript.
HTML Minifier — Minify HTML: remove comments and collapse whitespace while keeping pre, textarea and script blocks intact.
JavaScript Beautifier — Beautify minified or messy JavaScript with Prettier, using 2 or 4 spaces.
JavaScript Minifier — Minify JavaScript with Terser: remove whitespace and comments, compress and shorten variable names.
CSS Beautifier — Format CSS with one declaration per line and consistent spacing, using Prettier.
CSS Minifier — Minify CSS: strip comments and whitespace, shorten colours and zero units.
YAML Formatter — Format YAML with consistent indentation, after validating it, keeping comments and multiple documents.
Python Formatter — Clean up Python layout: 4-space indentation, PEP 8 blank lines, and spacing after commas and around operators.
Java Formatter — Re-indent Java code in K&R or Allman style with 2 or 4 spaces.
C# Formatter — Re-indent C# code in .NET (Allman) or K&R style.
C++ Formatter — Re-indent C and C++ code in K&R or Allman style.

Validation & regex

Regex Tester — Test regular expressions with flags, match highlighting, and capture groups.
Empty Catch Block Checker (C#) — Find empty, comment-only, and swallowing catch blocks with Roslyn.
Password Validation Regex Builder — Build a password-policy regex with your rules, plus ready-to-paste code for JavaScript, C#, Python and Java.
XML Validator — Check that XML is well-formed and see the exact line and column of the first error.
YAML Validator — Validate YAML syntax and get the line and column of any error.
Dockerfile Linter — Lint Dockerfiles for unpinned images, secrets in ENV, running as root, apt-get mistakes and more.
GitHub Actions Validator — Validate GitHub Actions workflows: structure, job dependencies, unpinned actions, script injection and permissions.
OpenAPI / Swagger Validator — Validate OpenAPI 3 and Swagger 2 specs: required fields, path parameters, duplicate operationIds and broken $refs.
Markdown Linter — Lint Markdown for heading structure, code fences, bare URLs, missing alt text and spacing.
Regex Generator — Get a tested regex for emails, URLs, phone numbers, postcodes, UUIDs, dates and more, with code for four languages.
Regex Cheat Sheet — Searchable regex syntax reference: character classes, quantifiers, groups, lookarounds and flags.
Email Regex — A practical email validation regex, tested against valid and invalid addresses, with code snippets.
URL Regex — A tested regex for http and https URLs, with test cases and code for JavaScript, Python, C# and Java.
Phone Number Regex — Phone number regex patterns for international E.164, US and UK numbers, tested live.

Code analysis

JavaScript Complexity Checker — AST-based cyclomatic complexity and maintainability for JavaScript and TypeScript snippets.
Code Complexity Checker (C#) — Roslyn cyclomatic complexity per method with configurable thresholds.
C# Code Quality Checker — Roslyn rules for empty catch, long methods, logging, and more—with a transparent score.
C# Code Smell Detector — Syntax heuristics for long methods, large classes, magic numbers, and nesting.
Static Code Analysis Tools — Guide to static analysis plus a live C# demo powered by CodeInspector rules.
Cyclomatic Complexity Calculator — Calculate McCabe cyclomatic complexity for every function in JavaScript, TypeScript, Python, Java, C#, C++, C or Go.
Cyclomatic Complexity Calculator for Java — Measure the cyclomatic complexity of Java methods online, with a rating per method.
Cyclomatic Complexity Calculator for Python — Calculate cyclomatic complexity for Python functions and methods, the same way radon and mccabe do.
Cyclomatic Complexity Calculator for C++ — Get the cyclomatic complexity of C++ functions and methods online.
Cyclomatic Complexity Calculator for C — Measure the cyclomatic complexity of C functions, with a rating for each one.
Cyclomatic Complexity Formula Calculator — Work out M = E − N + 2P from a control-flow graph, or M = decisions + 1, with the steps shown.
Code Smell Detector — Find long methods, deep nesting, duplicate code, magic numbers, empty catch blocks and other code smells in any language.
Duplicate Code Checker — Find copy-pasted blocks of code and see how much of a file is duplicated.
Magic Number Finder — Find unexplained numeric literals in code and replace them with named constants.
Technical Debt Calculator — Estimate technical debt in hours and cost, from pasted code or from your own numbers.
Technical Debt Ratio Calculator (SQALE) — Calculate the technical debt ratio and A–E maintainability rating with the SQALE method SonarQube uses.
Dead Code Finder — Find unreachable statements, always-false conditions and functions that are never called.
Function Length Checker — List every function by length and parameter count, and flag ones that are too long.
Deep Nesting Checker — Find functions with deeply nested if/for/while blocks and see how deep each one goes.
Code Readability Score — Score code readability from 0 to 100 using line length, function size, complexity, nesting, naming and comments.
Lines of Code Counter — Count total, code, comment and blank lines (SLOC) plus functions for pasted code.
TODO / FIXME Finder — List TODO, FIXME, HACK, XXX and BUG comments with line numbers.
Naming Convention Checker — Check function, class and variable names against each language's conventions.
Python Type Hint Coverage Checker — See which Python function parameters and return values have type hints, and your overall coverage.
Java Code Checker — Check Java code for common bugs and bad practices: string ==, printStackTrace, raw types, empty catch blocks and high complexity.
PEP 8 Checker — Check Python code against PEP 8: indentation, line length, whitespace, blank lines, comparisons to None and naming.
Python Code Checker — Find Python bugs: mutable default arguments, bare except, is with literals, eval, shadowed built-ins and more.
C++ Code Checker — Check C++ for unsafe string functions, raw new/delete, C-style casts, NULL and other modern C++ issues.
C Code Checker — Find buffer overflows and common C mistakes: gets, strcpy, printf format bugs, unchecked malloc and assignment in if.
JavaScript Code Checker — Lint JavaScript in your browser: ==, var, eval, innerHTML, debugger, console.log, unhandled promises and more.
TypeScript Code Checker — Find TypeScript type-safety leaks: any, non-null assertions, @ts-ignore, loose Object and Function types.
Unused Imports Finder — Find imports that are never used in Python, JavaScript, TypeScript, Java and Go.
Empty Catch Block Checker — Find empty catch blocks, except: pass and ignored Go errors in any language.

Developer utilities

C# Code Review Checklist — Interactive ten-category checklist with progress, notes, and Markdown export.
Cron Expression Generator — Build and validate 5-field Unix cron expressions with plain-English descriptions.
Base64 Encoder / Decoder — Encode and decode UTF-8 text with size indicators—not encryption.
JSON to C# Class — Generate C# classes from JSON objects with nested types and lists.
Diff Checker — Compare two texts line by line and highlight what was added and removed.
Code Diff Checker — Compare two versions of code side by side, ignoring indentation changes by default.
JSON Diff — Compare two JSON documents by structure, ignoring key order and formatting.
Code to Image — Turn code into a clean PNG image with syntax colours, ready for LinkedIn, X, slides and docs.
HTTP Status Codes — Look up any HTTP status code, what it means and how to fix common errors like 401, 403, 404, 500, 502, 503 and 504.
Hex to RGB Converter — Convert hex colours to RGB, RGBA, HSL, Android and C# formats, with a swatch and contrast ratios.
RGB to Hex Converter — Convert RGB, RGBA or HSL colours to hex, with a swatch and every common format.
Hex Color Codes & Picker — Find hex codes for CSS colour names (blue, white, green, orange, purple…) or convert any colour.
WCAG Contrast Checker — Check the contrast ratio between text and background colours against WCAG AA and AAA.
URL Encoder / Decoder — URL-encode or decode text, encode a full URL, or break a URL into its parts and query parameters.
HTML Entity Encoder / Decoder — Escape &, <, >, quotes (or all non-ASCII characters) as HTML entities, or decode entities back to text.
JSON Escape / Unescape — Escape text for use inside a JSON string (quotes, backslashes, newlines, tabs) or unescape it back.
Case Converter — Convert identifiers between camelCase, PascalCase, snake_case, SCREAMING_SNAKE, kebab-case and more.
Number Base Converter — Convert numbers between decimal, hex, binary and octal, including very large values.

Security

SQL Injection Code Checker — Find SQL built with string concatenation, interpolation or format() in Java, C#, Python, JavaScript, PHP and more.
API Key & Secret Leak Checker — Find hard-coded API keys, tokens, passwords, private keys and connection strings in code or config.
XSS Vulnerability Checker — Find XSS sinks in front-end and server code: innerHTML, document.write, dangerouslySetInnerHTML, v-html, Html.Raw and unescaped templates.
Regex DoS (ReDoS) Checker — Check regular expressions for catastrophic backtracking that can freeze a server.
.env File Validator — Validate .env files: syntax, duplicate keys, unquoted spaces, unclosed quotes and real-looking secrets.
PII in Logs Detector — Find log statements that write card numbers, CVVs, passwords, tokens, emails or other personal data.
JWT Security Checker — Audit a JWT for alg none, missing expiry, long lifetimes, missing audience, embedded keys and sensitive claims.

Fintech & payments

Money Calculation Bug Checker — Find money stored in float or double, BigDecimal(double), toFixed rounding and other currency bugs.
PCI DSS Developer Checklist — A developer-focused PCI DSS v4.0 checklist: card data storage, logging, secrets, secure coding and testing.
IBAN Validator — Validate IBANs for 70+ countries: country length and mod-97 checksum, with UK sort code breakdown.
Luhn Algorithm Checker — Check card numbers, IMEIs and other IDs with the Luhn (mod 10) algorithm, or calculate the check digit.
Test Credit Card Numbers — Test card numbers for Visa, Mastercard, Amex, Discover and RuPay, including declines and 3-D Secure.
Rounding Calculator — Round numbers with half-up, half-even (banker's), up, down, ceiling and floor using exact decimal maths.
Floating Point Precision Checker — See the exact value a double stores and how far 0.1 + 0.2 style calculations drift from the decimal answer.
SWIFT / BIC Validator — Validate SWIFT/BIC codes and break them into bank, country, location and branch.
ABA Routing Number Validator — Validate US ABA routing numbers with the 3-7-1 checksum and Federal Reserve prefix.
UK Sort Code Validator — Validate UK sort code and account number formats.

Hashing, JWT & passwords

Hash Generator — Generate MD5, SHA-1, SHA-256, SHA-384, SHA-512, SHA-3, Keccak-256, NTLM and CRC32 hashes at once.
MD5 Hash Generator — Generate an MD5 hash of any text, in hex or Base64, instantly in your browser.
MD5 Checker — Check whether text matches an expected MD5 hash.
SHA-1 Hash Generator — Generate the SHA-1 hash of any text in hex or Base64.
SHA-256 Hash Generator — Generate a SHA-256 hash of any text in hex or Base64.
SHA-384 Hash Generator — Generate a SHA-384 hash in hex or Base64, the format used for Subresource Integrity (SRI).
SHA-512 Hash Generator — Generate a SHA-512 hash of any text in hex or Base64.
SHA-3 & Keccak-256 Generator — Generate SHA3-224, SHA3-256, SHA3-384, SHA3-512 or Ethereum Keccak-256 hashes.
Bcrypt Hash Generator — Hash a password with bcrypt and a cost factor you choose.
Bcrypt Hash Checker — Check whether a password matches a bcrypt hash.
NTLM Hash Generator — Generate the NTLM (NT) hash of a password: MD4 of the UTF-16LE text.
Password Hash Generator — Create a salted PBKDF2-SHA256 (600,000 iterations) or bcrypt password hash.
Random Hash Generator — Generate cryptographically random 128-, 256- or 512-bit hex strings.
HMAC Generator — Generate HMAC-SHA256, SHA-512, SHA-1 or MD5 signatures in hex and Base64.
File Checksum Calculator — Calculate MD5, SHA-1, SHA-256, SHA-512 and CRC32 checksums of a file without uploading it.
CRC32 Checksum Calculator — Calculate the CRC32 checksum of text in hex and decimal.
JWT Decoder — Decode a JSON Web Token's header and payload, with human-readable expiry, issued-at and claims.
Bearer Token Decoder — Paste an Authorization: Bearer header and decode the token inside it, or learn why it can't be decoded.
JWT Generator — Create HS256, HS384 or HS512 signed JWTs from a JSON payload and secret, for testing APIs.
Password Strength Checker — Check password strength, entropy and estimated crack time, with tips to improve it. Nothing leaves your browser.
Password Generator — Generate strong random passwords or memorable passphrases with the browser's secure random generator.

Generators

UUID Generator — Generate up to 1,000 UUIDs at once: version 4 (random), version 7 (time-ordered) or version 1.
GUID Generator — Generate GUIDs in the format you need: uppercase, {registry}, no hyphens, C# or SQL Server.
UUID Validator — Check whether values are valid UUIDs and see their version, variant and (for v7) creation time.
Lorem Ipsum Generator — Generate lorem ipsum paragraphs, sentences, words, lists or HTML.
Dummy Text Generator (English) — Generate readable English placeholder text instead of Latin.
Mock Data Generator — Generate fake test data as JSON, CSV or SQL INSERT statements from a simple field list.
Cron Expression Explainer — Explain any cron expression in plain English and list its next five run times.
Quartz Cron Generator — Build Quartz and Spring @Scheduled cron expressions with seconds, ?, L and #.
.gitignore Generator — Generate a .gitignore for Node, Python, .NET, Java, Go, C++, IDEs and operating systems, with secrets always excluded.
README Generator — Generate a clean README.md with install, usage, tests, contributing and license sections.
Open Source License Generator — Generate MIT, ISC, BSD, Unlicense text or Apache 2.0 and GPL-3.0 file headers with your name and year.

Date & time

Epoch & Unix Timestamp Converter — Convert Unix timestamps (seconds, ms, µs or ns) to dates in UTC and major time zones, and dates back to epoch.
Time Zone Converter — Convert a date and time between UTC, US, UK, Europe, India, Singapore, Japan and Australia, with daylight saving.
Time Difference Calculator — Calculate the exact time between two dates in days, hours, minutes, seconds, weeks and weekdays.
UTC to Eastern Time Converter — Convert UTC to US Eastern Time (EST or EDT) for any date, with daylight saving handled.
ISO 8601 Date Converter — Convert dates to every ISO 8601 form (UTC, offset, week date, ordinal) and decode durations like P1DT2H.
Date Format Converter — Translate date format patterns between Python strftime, Java, C#/.NET, JavaScript (dayjs) and PHP.

Converters

JSON to YAML Converter — Convert JSON to clean, readable YAML.
YAML to JSON Converter — Convert YAML (including multi-document files) to JSON.
JSON to CSV Converter — Convert a JSON array to CSV, flattening nested objects into dotted columns.
CSV to JSON Converter — Convert CSV to JSON objects or arrays, with types detected and the delimiter auto-detected.
JSON to XML Converter — Convert JSON to well-formed, indented XML.
XML to JSON Converter — Convert XML to JSON, keeping attributes as @name keys and repeated elements as arrays.
JSON to Java POJO — Generate Java POJOs, Lombok @Data classes or records with Jackson annotations from JSON.
JSON to Python Dataclass — Generate Python dataclasses, Pydantic models or TypedDicts with type hints from JSON.
JSON to TypeScript — Generate TypeScript interfaces, type aliases or Zod schemas from JSON.
JSON to Go Struct — Generate Go structs with json tags from JSON.
JSON to SQL INSERT — Turn a JSON array into CREATE TABLE and INSERT statements for PostgreSQL, MySQL or SQL Server.
cURL to Code Converter — Convert a cURL command to Python requests, JavaScript fetch, C# HttpClient, Java HttpClient or Go.
SQL to MongoDB Converter — Convert SQL SELECT, UPDATE and DELETE queries to MongoDB find, aggregate, updateMany and deleteMany.