Free Online Developer Tools
Fast, privacy-friendly utilities that run entirely in your browser. No sign-up, no uploads, no tracking of your data.
Account apps
Hosted services that need a free Google or GitHub sign-in.
AI
JSON
JSON Formatter
Format, validate and minify JSON online for free. Pretty-print JSON with syntax highlighting and locate syntax errors instantly — right in your browser.
JSON Viewer
View and explore JSON as a collapsible tree online for free. Navigate nested objects and arrays with syntax highlighting — private in your browser.
JSON Compare
Compare two JSON documents online and see every difference — added, removed and changed values with exact paths. Free JSON diff tool.
JSON Repair
Fix broken JSON online for free. Repairs comments, single quotes, unquoted keys, trailing commas and JS/Python literals automatically.
JSON Escape & Unescape
Escape and unescape JSON strings online for free. Convert text to a valid JSON string literal and back — runs in your browser.
JSONPath Tester
Test JSONPath expressions online for free. Run queries against your JSON, see live match counts and flattened results — powered by jsonpath-plus.
JSON Converter
Convert JSON to YAML, CSV or XML online for free. Fast, privacy-friendly conversion that runs entirely in your browser — no upload required.
JSON to JSON Schema
Generate a JSON Schema (draft 2020-12) from example JSON online for free. Types, required fields and nesting inferred automatically.
JSON to Code
Generate TypeScript, JavaScript, Java, Python, Go and C# classes from JSON online for free. Type-safe model generation in your browser.
JSON to TypeScript
Convert JSON to TypeScript interfaces online — nested objects become named interfaces, optional fields detected across arrays. Free, no upload.
JSON to Zod Schema
Generate Zod schemas from JSON online — nested objects become named z.object() schemas with .nullish() optionals and a z.infer type export. Free, no upload.
JSON Schema to Code
Generate type models from a JSON Schema online — TypeScript interfaces, Java records, Python dataclasses, Go, Rust and more. $ref, allOf and required handled.
JSON Flatten & Unflatten
Flatten nested JSON to dot/bracket keys online — or unflatten flat keys back to nested objects and arrays. Custom separators, lossless round-trip, no upload.
OpenAPI & Swagger Validator
Validate OpenAPI 3.x and Swagger 2.0 documents online — structural checks, $ref resolution, endpoint listing and stats. JSON or YAML, paste or fetch — free, no signup.
XML
XML Formatter
Format, validate and minify XML online for free. Pretty-print XML documents with configurable indentation and catch tag errors — in your browser.
XML to JSON Converter
Convert XML to JSON or YAML online for free. Attributes, nested elements and repeated tags handled automatically — private in-browser conversion.
XML to Code
Generate TypeScript, Java, Python, Go and C# classes from XML online for free. Attributes and repeated elements mapped automatically — in your browser.
XPath Tester
Test XPath expressions online — paste XML, enter an XPath query and see matched nodes, attributes and scalar results instantly. Runs locally.
YAML
Converters
CSV to JSON
Convert CSV to JSON online for free. Header-based mapping, quoted fields and type detection — instant conversion in your browser.
JSON to CSV Converter
Convert JSON arrays to CSV online — nested objects flattened automatically, paste or drop JSON and download the CSV. No upload.
Excel to JSON
Convert Excel to JSON online — drop an .xlsx or .csv file, pick a sheet and get structured JSON rows. Files never leave your browser.
JSON to SQL Converter
Convert JSON or CSV to SQL INSERT statements online — CREATE TABLE with inferred column types, MySQL/PostgreSQL/SQLite/SQL Server/Oracle dialects. Reverse: parse INSERTs back to JSON.
Markdown to HTML Converter
Convert Markdown to clean HTML online for free. Sanitized output, optional full document wrapper, GFM tables and code blocks — copy or download the .html file.
Timestamp Converter
Convert Unix timestamps to readable dates and back online for free. Seconds and milliseconds, local and UTC output, live epoch clock — all in your browser.
Timezone Converter
Convert times between timezones online for free. See a wall-clock time rendered in 20 common zones plus Unix/ISO output — powered by the Intl API.
Integer Base Converter
Convert integers between binary, octal, decimal and hexadecimal online for free. Supports 0x/0b/0o prefixes, negative values and arbitrarily big numbers.
Color Converter
Convert colors between HEX, RGB and HSL online for free. Native color picker, live swatch and WCAG contrast ratios against black and white.
TOML Converter
Convert TOML to JSON and back online for free. Parse and serialize TOML configs — pyproject.toml, Cargo.toml — locally in your browser.
.env Converter
Convert .env files to JSON or YAML and back online for free. Handles quotes, comments and multiline escapes — perfect for config migrations.
Chmod Calculator
Unix chmod calculator online — convert file permissions between the rwx checkbox matrix, octal notation (755) and symbolic form (u=rwx).
Text
Text Compare
Compare two texts line by line online for free. See added and removed lines highlighted instantly — a fast, private diff tool.
Diff & Patch Generator
Create unified diff patches online — compare two texts into a .patch file with configurable context, or apply a patch back (even reverse). GNU patch compatible format.
Regex Tester
Test regular expressions online with live match highlighting, capture group details and full JavaScript flag support. Free regex debugger and playground.
Markdown Preview
Write and preview Markdown online for free. Live GitHub-flavoured rendering with tables and code blocks, sanitized HTML output — all in your browser.
HTML Preview
Free online HTML viewer and editor — paste HTML and see a live rendered preview in a sandboxed iframe, side by side with your markup.
SQL Formatter
Format and beautify SQL online for free. Dialect support for MySQL/MariaDB, PostgreSQL, SQLite and T-SQL, keyword casing and indentation options.
Case Converter
Convert text between camelCase, PascalCase, snake_case, kebab-case, UPPER, Title and more — online for free, all variants shown at once.
Text Line Tools
Sort, dedupe, reverse, shuffle, trim and number text lines online for free. Chainable line operations with live line counts — all local.
Word Counter
Free online word counter — count words, characters, sentences and paragraphs, estimate reading time and see your most frequent words. No upload.
Token Counter
Count LLM tokens online — GPT-4o, o3, GPT-4 and Claude encodings with context-window usage and API cost estimate. Runs locally, no upload.
JavaScript Minifier
Minify JavaScript online with Terser — remove whitespace and comments, mangle variable names and compress code. Shows byte savings.
CSS Minifier
Minify CSS online with csso — strip whitespace and comments, merge duplicate rules and shorthand properties. Shows byte savings, all local.
Encoding
Base64 Encoder & Decoder
Encode and decode Base64 online for free. Unicode-safe Base64 conversion with optional URL-safe output — runs entirely in your browser.
URL Encoder & Decoder
Encode and decode URLs and query parameters online for free. Percent-encode special characters safely, directly in your browser.
JWT Decoder
Decode and inspect JWT tokens online for free. View header, payload and claims with readable dates, check expiry, verify HMAC signatures — locally in your browser.
Unicode Converter
Convert text to Unicode code points and back online for free. U+ notation, JS escapes, HTML entities, UTF-8/UTF-16 bytes — with a per-character inspector.
HTML Entity Converter
Encode and decode HTML entities online for free. Named, numeric or minimal escaping for accented characters, symbols and markup — two-way conversion.
Security
JWT Encoder
Create and sign JWT tokens online for free. HS256/384/512 HMAC signing via Web Crypto — the counterpart to our JWT decoder, fully local.
HMAC Generator
Compute HMAC-SHA256/384/512 online for free. Keyed message authentication codes via Web Crypto — the secret never leaves your browser.
Bcrypt Hash Generator
Generate and verify bcrypt password hashes online for free. Adjustable cost factor (4–15 rounds) — computed locally with bcryptjs.
htpasswd Generator
Generate .htpasswd entries online — create bcrypt password lines for Apache and nginx basic auth with adjustable cost. Runs locally.
Password Strength Checker
Check password strength online — zxcvbn-based scoring with crack-time estimates for online and offline attacks, plus improvement tips. Fully local.
TOTP Generator
Generate TOTP codes online — paste a base32 secret or otpauth:// URI and get live 6-digit two-factor codes with countdown. Fully client-side.
SRI Hash Generator
Generate Subresource Integrity hashes online — SHA-256/384/512 integrity attributes for scripts and stylesheets, computed locally.
CSP Generator
Build a Content-Security-Policy header online — pick directives and sources, get the policy string and meta tag variant instantly.
Generators
UUID Generator
Generate UUID v4 or v7 identifiers online for free. Bulk-generate up to 100 cryptographically secure UUIDs and copy them with one click.
UUID v7 Generator
Generate UUID v7 identifiers online for free — time-ordered, sortable UUIDs that embed a millisecond timestamp. Bulk generation, copy with one click.
ULID Generator
Generate ULIDs online for free — 26-char, URL-safe, lexicographically sortable identifiers. Monotonic batch generation, lowercase option, copy with one click.
Nano ID Generator
Generate Nano IDs online for free — compact, URL-safe, cryptographically strong random IDs. Custom length and custom alphabet, bulk generation.
Hash Generator
Generate SHA-1, SHA-256, SHA-384 and SHA-512 hashes online for free. Instant cryptographic digests of any text, computed in your browser.
Password Generator
Generate strong random passwords online for free. Adjustable length and character sets, entropy estimate, bulk generation — crypto-secure in your browser.
QR Code Generator
Generate QR codes online for free. Custom size and error-correction level, SVG and PNG download — everything runs locally in your browser.
Lorem Ipsum Generator
Generate lorem ipsum placeholder text online for free. Paragraphs, sentences or words with optional classic opener — copy with one click.
Cron Expression Explainer
Translate cron expressions to plain English online for free. Field breakdown for the classic 5-field syntax and the 6-field variant with seconds — powered by cronstrue.
Cron Next Run Times
Calculate the next fire times of a cron expression online — see exactly when your schedule runs, in local time or UTC. 5-field and 6-field (seconds) syntax supported.
Cron Expression Generator
Build cron expressions visually — pick minutes, hours, days, months and weekdays, then copy a ready-to-paste crontab line with plain-English description and next run times.
Markdown Table Generator
Create Markdown tables online — edit cells in a visual grid, import TSV/CSV data, set column alignment and copy the generated Markdown.
CSS Gradient Generator
Create CSS gradients online — visual linear, radial and conic gradient editor with color stops and angle, copy the generated background rule.
gitignore Generator
Generate a .gitignore file for your stack — pick languages, frameworks, OS and editors and get a combined file instantly.
AI Rules Generator
Generate rules files for AI coding assistants — CLAUDE.md, AGENTS.md, Cursor rules, Copilot instructions and Windsurf, from stack-aware building blocks.
Favicon Generator
Generate a complete favicon set from one image — multi-size ICO, PNG icons, apple-touch-icon and the HTML link tags. Free, no upload.
Web & SEO
Robots.txt Generator
Generate a robots.txt file online — user-agent rules, disallow paths, crawl-delay and sitemap directive, ready to download.
robots.txt Validator
Validate a robots.txt file online — directive syntax, rules outside agent groups, duplicates, sitemap URLs, Google's 500 KB limit. Paste content or fetch a live file.
sitemap.xml Validator
Validate a sitemap.xml online — XML errors, missing or non-absolute loc URLs, duplicates, bad lastmod/changefreq/priority values, 50,000 URL and 50 MB limits. Paste or fetch.
Meta Tag Generator
Generate HTML meta tags online — title, description, canonical, Open Graph and Twitter Card tags ready to paste into your head section.
SERP Preview Tool
Preview how your page looks in Google search results — title, URL and description snippet with live character counters, desktop and mobile.
llms.txt Generator
Create an llms.txt file for your website — the markdown index that helps LLMs find your docs, APIs and key pages. Copy or download instantly.
.htaccess Generator
Generate an Apache .htaccess file online — HTTPS redirect, www/non-www canonical, 301 redirects, SPA fallback, gzip and caching rules.
DevOps
docker run → Compose
Convert docker run commands to docker-compose.yml online — flags, ports, envs, volumes, healthchecks and limits mapped. Free, no upload.
Nginx Config Generator
Generate an nginx server config online — static site, SPA fallback or reverse proxy with SSL, gzip, CORS and caching. Free, no signup.
Kubernetes YAML Validator
Validate Kubernetes YAML online — structural and kind-specific checks for Deployments, Services, Ingress, RBAC and more. Multi-doc, free, no upload.
Images
Image Converter
Convert images between PNG, JPEG, WebP and AVIF online for free — HEIC and TIFF inputs supported, drop multiple files to batch-convert. Processing happens in your browser, no upload.
Image Compressor
Compress images online for free — reduce JPEG, PNG, WebP or AVIF file size with a quality slider, optional downscaling and a before/after preview. Also opens HEIC and TIFF photos. Files never leave your browser.
Image Cropper
Crop images online for free — drag a crop box or lock an aspect ratio, download as PNG, JPEG or WebP. Also opens HEIC and TIFF. Files never leave your browser.
Background Remover
Remove image backgrounds online for free — AI-powered cutout to a transparent PNG or WebP. Runs entirely in your browser: photos are never uploaded.
Image to Base64
Convert images to Base64 or data URI online for free. Drag & drop PNG, JPG, SVG or WebP and get embeddable Base64 — files never leave your browser.
Base64 to Image
Decode Base64 to an image online for free. Preview data URIs and Base64 strings, inspect size and type, download the file — all local.
Image to Text (OCR)
Extract text from images online — free OCR for screenshots, scans and photos in 30+ languages. Batch support, runs locally in your browser, no upload.
Image to SVG
Convert PNG, JPG or WebP images to SVG vector graphics online for free. Adjustable colors, detail and black & white tracing — files never leave your browser.
SVG Optimizer
Optimize SVG online with SVGO — remove metadata, comments and redundant precision to shrink file size. Preview and copy the optimized markup.
SVG to PNG Converter
Convert SVG to PNG online for free — paste SVG markup or drop a .svg file, choose the output size and download a transparent PNG instantly.
SVG to ICO Converter
Convert SVG logos to ICO favicons online — rendered at up to 256px with transparency, all in your browser. No upload.
PNG to ICO Converter
Convert PNG to ICO favicon online — up to 256px, transparency preserved, generated locally in your browser. No upload.
HEIC to JPG Converter
Convert HEIC photos to JPG online for free — iPhone and iPad photos decoded in your browser, no upload, batch supported.
HEIC to PNG Converter
Convert HEIC to PNG online — lossless PNG output for iPhone photos, processed in your browser without uploading. Batch supported.
AVIF to JPG Converter
Convert AVIF images to JPG online — fix compatibility issues with apps that cannot open AVIF. Runs locally in your browser.
JPG to PNG Converter
Convert JPG to PNG online free — lossless PNG output rendered locally in your browser, no upload required. Batch supported.
WebP to PNG Converter
Convert WebP images to PNG online — transparency preserved, works in your browser with no file upload. Batch conversion supported.
PNG to WebP Converter
Convert PNG to WebP online — much smaller files with transparency intact. Local browser conversion, no upload, batch supported.
Image Resizer
Resize images online for free — exact pixel size, fit inside a box or percentage scaling, with social media presets and batch download. Files never leave your browser.
Resize Image for Instagram
Resize a photo for Instagram online — fit to 1080×1080 square or 1080×1920 story size without cropping. Free, no upload, runs in your browser.
YouTube Thumbnail Resizer
Resize an image to YouTube thumbnail size online — fit to 1280×720 without cropping. Free, no upload, runs in your browser.
Merge PDF
Merge PDF files online for free — combine multiple PDFs into one document in the order you choose. Files never leave your browser.
Split PDF
Split a PDF online for free — extract a page range into one file or save every page as a separate PDF in a ZIP. Runs in your browser, no upload.
PDF Compressor
Compress PDF files online for free — reduce PDF size with three quality presets, or keep text selectable with a lossless re-save. No upload needed.
JPG to PDF Converter
Convert JPG to PDF online for free — combine JPG, PNG, WebP or HEIC photos into one PDF, fit to image size or A4/Letter. No upload, runs in your browser.
PDF to JPG Converter
Convert PDF to JPG or PNG online for free — render each page at 96, 150 or 300 dpi and download single pages or all of them as a ZIP. Runs locally, no upload.
3D
G-code Viewer
View and analyze 3D printing G-code online for free — layer-by-layer toolpath preview, print time, filament usage and slicer stats. Files never leave your browser.
STL & 3MF Viewer
View STL files in 3D online for free — rotate and zoom a shaded preview, inspect volume, surface area, dimensions and manifold errors. Files never leave your browser.
Lithophane Generator
Turn a photo into a 3D-printable lithophane online — flat panel, curved arc or cylinder lampshade STL with a live 3D preview. Free, no upload, no signup.
Text to STL Generator
Turn text into a 3D-printable STL online — name plates, keychains with a hole and rounded corners, or free-standing letters. Live 3D preview, free, no upload.
Filament Calculator
Convert filament length to weight and back online for free — meters ↔ grams by material density and diameter, plus a spool-remaining calculator.
Print Time Estimator
Estimate 3D print time and filament use from an STL file online for free — layer count, deposited volume, toolpath length and a realistic time range. No slicer needed.
3D Printing Cost Calculator
Calculate 3D printing costs online for free — filament, electricity, printer wear, labor, failure buffer and profit margin. Get a suggested selling price per unit.
Temp Tower Generator
Generate printable calibration towers online for free — temperature, retraction distance/speed, flow rate, pressure advance and fan G-code with per-segment values.
Networking
Subnet Calculator
Calculate IPv4 subnets online for free. Enter a CIDR like 192.168.1.10/24 to get netmask, network, broadcast, host range and usable host count.
URL Parser
Parse URLs online — split any URL into scheme, host, port, path, query parameters and fragment, with copy buttons for each part. Free and private.
User-Agent Parser
Parse User-Agent strings online — identify browser, engine, OS, device type and CPU architecture from any UA string. Your own UA prefilled.
CORS Tester
Test CORS headers on any URL from your browser — send a real request, inspect the response headers, and see whether cross-origin reads are allowed, blocked or preflighted.
cURL to Code Converter
Convert cURL commands to code online — turn any curl command into fetch, axios, Python requests, Go, PHP or Rust code. Free, runs in your browser.
Reference
HTTP Status Codes
HTTP status code reference — searchable list of all standard 1xx–5xx codes with names and plain-English descriptions, free online.
ASCII Table
ASCII table reference online for free — all 128 characters with decimal, hex, glyph and control-code names, searchable by any format.
Semver Checker
Check semantic versions online — parse versions, compare two releases, bump major/minor/patch/prerelease and test npm-style ranges like ^1.2 or 1.x for free.
Mail Blackhole Comparison
Free email sandbox plans compared — Mailtrap, Mailisk, Mailloop and MailSlurp vs our Mail Blackhole fake SMTP mailboxes: monthly quotas, retention, API, IMAP and webhooks.
Watchdroid Comparison
Free uptime monitoring compared — UptimeRobot, Better Stack, Healthchecks.io, StatusCake and Uptime Kuma vs our Watchdroid monitors: monitor counts, check intervals, heartbeat/cron support, alerts and status pages.