developer tools, private by default
78+ tools that run entirely in your browser — open DevTools → Network and watch nothing happen. No signup, no ads, no telemetry on your input; the rare tool that needs a server says exactly what it does. Need the same work server-side or at scale? It's a no-signup, pay-per-call developer API — your credit key is the API key.
- tools
- 78
- signup
- none
- API
- pay-per-call
The free browser-side tools are open source — run your own copy
Every free tool here is client-side, so the whole site is static: clone it, run one
docker build, and self-host it anywhere — or just read the source. MIT licensed,
no tracking, nothing to sign up for.
# pay-per-call
No-signup — your credit key is the API key. The Developer API + Pro tools, billed in credits. docs & pricing →
Transcribe hours of audio — podcasts, meetings, lectures, interviews
Drop a long audio or video file. It's split in your browser with ffmpeg.wasm, sent to cloud Whisper in pieces, then stitched back into one clean transcript — export TXT, SRT, or VTT. Pay only for the minutes you transcribe with a credit key: no account, no subscription, nothing kept.
Transcribe a file →# dev [35]
parsers, calculators, converters, validators
Regex Tester
Test, debug, and explain regular expressions.
JWT Decoder & Verifier
Decode and verify JSON Web Tokens (HS256, RS256, ES256) in your browser.
Color Picker & WCAG Contrast
Hex / RGB / HSL / OKLCH / HWB conversion, WCAG contrast, image palette extraction, Tailwind-style scale from any color.
Diff Checker
Compare two texts or JSON documents. Line, word, char, and JSON-aware modes.
Cron Expression Builder & Tester
Describe any cron expression in plain English and preview the next 10 fires in your timezone.
Hash Generator
MD5, SHA-1, SHA-256, SHA-384, SHA-512 of text or files in your browser. Hex / Base64 / Base64url.
curl Converter
Convert a curl command to fetch, axios, Python, Go, Rust, and 10 more targets.
CIDR Calculator
IPv4 subnet math: network, broadcast, host range, mask, split, contains check.
Base64 Encoder & Decoder
Encode/decode Base64 in your browser. Text and file modes, standard and URL-safe variants. UTF-8 aware.
Base Converter
Convert integers between decimal, binary, hex, and octal. BigInt-backed.
Unix Timestamp Converter
Convert Unix timestamp ↔ ISO 8601 / local / UTC. Auto-detect seconds vs ms vs μs. Live ticker.
Time Duration Calculator
Hours and minutes between two times. Overnight wraparound, break deduction, decimal-hours output.
Slug Generator
Turn any string into 7 case styles: kebab, snake, camel, pascal, dot, title, SCREAMING_SNAKE.
A/B Test Significance Calculator
Two-proportion z-test with p-value, confidence interval, and relative lift. 90 / 95 / 99% levels.
HAR File Viewer
Open .har captures from Chrome / Firefox DevTools. Filter, inspect headers and bodies. Local-only.
GraphQL Schema Visualizer
Browse GraphQL SDL types, fields, args, unions, enums, interfaces. Cross-type navigation.
URL Encoder / Decoder
Percent-encode and decode URLs. Component, full-URL, and form modes. URL parts breakdown.
HTML Entity Encoder / Decoder
Encode HTML entities (& < > ") or decode entity-escaped text. Named, decimal, hex modes.
HTTP Status Code Reference
Every HTTP status code with description, RFC source, and typical use. Searchable by code, name, or use-case.
HTTP Request Client
Send any HTTP request (GET/POST/PUT/PATCH/DELETE) with custom headers + body, see the full response, copy as curl. CORS-free via an edge proxy.
AI Regex Generator
Describe what to match in plain English, get a regex + explanation, and test it in one click. Free, no signup.
AI Commit Message Generator
Paste a git diff, get a clean Conventional Commit message. Free, no signup. The diff is sent to an AI model and not stored.
Unicode / Emoji Inspector
Break any string into code points, categories, escapes (JS / HTML / URL), and NFC/NFD/NFKC/NFKD normalization. In your browser.
CSS Unit Converter
Convert px ↔ rem ↔ em ↔ pt ↔ % ↔ vw ↔ vh. Configurable root font-size and viewport.
What's My IP Address
See your public IP, network (ASN), approximate location, and TLS/HTTP connection details. Read at the edge, stored nowhere.
HTTP Header Checker
Inspect any URL's response headers, follow its redirect chain, and grade its security headers (HSTS, CSP, X-Frame-Options). Runs on the edge, stores nothing.
Mock REST API
Paste a JSON (or any) response, pick a status and content-type, and get a stable public endpoint that returns it. Free fake API. No signup.
Pastebin
Paste text or code, get a shareable link that expires (1 hour to 30 days). No account, no ads.
Temp Mail (Disposable Inbox)
Generate a throwaway, receive-only email address, catch a verification message, and let it self-destruct in an hour. No signup. Anti-abuse by design.
Webhook Tester
Get a temporary URL, point any webhook at it, and watch incoming requests — method, headers, body — arrive live. Free, no signup. Bins auto-expire in 24h.
Email Auth Checker (SPF · DKIM · DMARC)
Check a domain's SPF, DKIM, and DMARC records and get a plain-English verdict on spoofing protection. Live DNS lookups on the edge — nothing stored.
DNS Lookup
Look up A, AAAA, MX, TXT, CNAME, NS, and more for any domain. Run on the edge via DNS-over-HTTPS — your browser never makes the query and nothing is stored.
CT Subdomain Finder
Find every subdomain and TLS certificate a domain published to Certificate Transparency logs. Passive recon via crt.sh on the edge — no packets to the target.
LLM Token Counter
Count tokens and estimate API cost for GPT-5, GPT-4o, Claude, Gemini, and DeepSeek — with a live token visualizer. Exact OpenAI tokenization, 100% in your browser.
Claude Tool Schema Validator
Check Claude tool definitions for anything the Messages API would reject, and convert OpenAI functions and MCP tools to Anthropic format.
# data [16]
JSON, YAML, TOML, CSV, Markdown shape-shifting
JSON to CSV Converter
Convert JSON to CSV and back. 100% in your browser.
Markdown ↔ HTML Converter
Convert GitHub-flavored Markdown to HTML and back. Live preview, syntax highlighting.
PDF to Markdown & JSON
Extract a PDF to clean Markdown or structured JSON, entirely in your browser. Headings, paragraphs, per-page text. No upload, no signup.
HTML to JSON, Markdown & Text
Paste HTML, get a structured JSON outline, clean Markdown, or plain text — in your browser. Optional AI extraction into your own JSON schema.
JSON Formatter & Error Reviewer
Validate, pretty-print, and minify JSON. Pinpoint syntax errors by line and column.
JSON ↔ YAML Converter
Convert JSON to YAML and back. Kubernetes-friendly, block or flow style, sort keys.
JSON to Types Generator
Generate TypeScript, Zod, Go, Rust, Python, and 6 more languages from a JSON sample.
Mock Data Generator
Generate fake JSON / JSON Lines / CSV / SQL INSERT records from a template. Powered by faker.
TOML ↔ JSON Converter
Convert between TOML and JSON. Tables, arrays of tables, dates. Bidirectional via smol-toml.
SQL Playground
Run real SQLite in your browser — empty DB, open a .sqlite file, or import a CSV. Query and export, all client-side (WASM). No upload.
CSV Viewer
Open a CSV, filter and sort it, export to CSV or JSON — entirely in your browser. No upload, no row paywall.
CSV → Chart
Turn CSV data into a bar, line, or pie chart and export as SVG — in your browser, nothing uploaded.
XLSX ↔ CSV / JSON
Convert Excel/ODS spreadsheets to CSV or JSON and back to XLSX — in your browser, nothing uploaded.
JSON ↔ XML Converter
Convert JSON to XML and back, both directions, in your browser. Attributes and text nodes preserved. No upload.
PDF Metadata Stripper
Inspect and remove PDF Info dictionary + XMP metadata in your browser. Field-level toggle, before/after view.
Markdown Table Generator
Paste CSV / TSV / pipe-separated rows. Output a GitHub-flavored Markdown table with column alignment.
# image [10]
pixel-pushers — compress, resize, convert, optimize, render
Image Compressor
Compress JPG, PNG, and WebP without quality loss.
Image Size Converter
Resize JPG, PNG, and WebP to exact pixel dimensions.
EXIF Viewer & Stripper
Inspect and remove camera, GPS, and personal metadata from images. Lossless.
Image Format Converter
Convert JPG ↔ PNG ↔ WebP in your browser. Batch, quality control, lossless WebP.
SVG Optimizer
Shrink SVG with SVGO: strip editor cruft, round numbers, preserve rendering. Runs in your browser.
Mermaid Diagram Renderer
Render flowcharts, sequence, class, state, ER, Gantt, and pie diagrams from Mermaid source. Export SVG / PNG.
Aspect Ratio Calculator
Simplify W×H to a ratio, or derive the missing dimension from a target ratio. 8 common presets.
Watermark Remover
Brush over a watermark; the tool inpaints the area from surrounding pixels. Browser-only. Modest quality by design.
Background Remover
Strip image backgrounds with BiRefNet running locally in your browser. PNG with alpha or solid color replacement.
Image to Text (OCR)
Extract text from screenshots, scans, and photos in 10 languages. tesseract.js, runs in your browser.
# video & audio [7]
record, transcribe, trim, split, compress — in your browser
Video Splitter & Joiner
Split videos into clips or merge into one. One-click export to 1080×1920 vertical MP4 for YouTube Shorts and TikTok. Browser-only, no upload.
Video Compressor
Compress MP4, MOV, WebM, MKV, AVI to smaller MP4 (H.264 + AAC). Three quality presets, optional resolution cap. Runs entirely in your browser.
YouTube Shorts & TikTok Converter
Resize any video to 1080×1920 vertical MP4 for YouTube Shorts, TikTok, and Instagram Reels. Pad or crop mode. Browser-only, no upload.
Shorts Safe Zone & Pre-flight Checker
Check a Short before you post it: safe-zone overlay for YouTube Shorts, TikTok and Reels, plus format, loudness (LUFS), silent intro, black opening frame, cuts and loop point. Runs in your browser.
Audio to Text Transcriber
Transcribe audio & video files with Whisper running locally in your browser. Export TXT, SRT, VTT. Includes SRT/VTT subtitle converter. No upload.
Long Audio Transcription
Transcribe hours-long audio & video — podcasts, meetings, lectures — with cloud Whisper. Files are split in your browser and sent in pieces. Export TXT, SRT, VTT. Credits, no signup.
Audio Recorder
Record from any microphone and download as WebM, WAV, MP3, M4A, or OGG. Optional local Whisper transcription. Browser-only, no upload.
# generator [10]
spit out fresh bytes — IDs, passwords, QR, favicons, ASCII
QR Code Generator with Logo
Generate branded QR codes with a custom logo overlay.
Color Palette Generator
Press space to generate harmonious palettes. Lock favorites, regenerate the rest. Export CSS, JSON, SVG, PNG.
Favicon & App Icon Generator
Web favicon pack, iOS AppIcon.appiconset, Android launcher (mipmap + adaptive), or custom-size zip — from one image.
UUID Generator
UUID v4 / v7, ULID, Nano ID, hex token, short ID. Crypto-secure. Batch up to 1000.
Password Generator
Strong random passwords or XKCD-style passphrases. Crypto-secure, ambiguous-char exclusion, entropy meter.
ASCII Art Generator
Turn text into ASCII banners with 10 figlet fonts. Standard, Big, Slant, ANSI Shadow + more.
URL Shortener
Shorten a long link so it fits in a simpler, easier-to-scan QR code. The one tool here with a server — and it tells you exactly what it stores.
Tier List Maker
Drag-and-drop S/A/B/C/D tier lists. Upload images, customize tiers, export PNG. Browser-only, auto-saves locally.
One-Time Secret
Share a password or note via a link that works once, then self-destructs. End-to-end encrypted in your browser — the server only holds an unreadable blob.
Temp File Share
Upload a file (up to 25 MB), get a shareable link that expires in 1 hour to 7 days, then auto-deletes. No signup. Guarded to always stay $0.
# games [14]
mini-games — hands, face, or voice as the controller, nothing leaves the tab
6-7 Hand Cam
[camera]Move your hands on the beat or smash falling 6s and 7s. Webcam hand tracking, in-browser.
play →
Rock Paper Scissors Cam
[camera]Throw real hand gestures at your webcam and beat the AI — first to 5 wins.
play →
Finger Ninja
[camera]Slice flying code glyphs with your fingertips — webcam fruit ninja, no install.
play →
Hand Pong
[camera]Pong with your hand as the paddle — vs AI or 2 players sharing one webcam.
play →
Air Piano
[camera]Falling-note rhythm game played with your fingertips in the air — webcam + WebAudio.
play →
Flappy Arms
[camera]Flap your actual arms to fly the bird through pipes — webcam body tracking.
play →
Squat Dodge
[camera]Lean and squat to dodge incoming walls — a webcam workout disguised as a game.
play →
Face Flappy
[camera]Open your mouth to flap — flappy bird steered entirely by your face.
play →
Scream Jump
[mic]Scream (or hum) to fly — a voice-controlled rocket run, 100% local audio.
play →
Daily Hex
Guess the color's hex code in 6 tries — a new puzzle every day, same for everyone.
play →
Reflex Lab
Reaction time, aim, number memory, typing burst — benchmark yourself, locally.
play →
The Pale One
Find 8 pages in a dark PS1-style forest while a tall, faceless figure blinks closer. First-person WebGL horror, nothing saved.
play →
Cube Miner
A blocky voxel sandbox in PS1 style — break and place blocks, walk or fly a procedural island. In-browser, nothing saved.
play →
Dead City
Over-the-shoulder PS1-style zombie shooter — clear city streets with infinite handgun ammo, grab health, push deeper. In-browser, nothing saved.
play →# recent writing
view all →-
Math.max(...array) throws a RangeError once the array gets big
Spreading an array into a function call passes every element as a separate argument. Past roughly 125,000 elements Node 26 throws 'Maximum call stack size exceeded', which breaks Math.max, push(...items) and String.fromCharCode-based base64.
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Number('') is 0, so a blank field passes numeric validation
Number() and unary plus turn an empty or whitespace-only string into 0, not NaN, so isNaN checks, Zod's coerce.number() and an empty PORT= line all accept blank as zero. Check for empty before converting.
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Returning a promise from try skips your catch
Inside an async function, return fetchUser() in a try block hands the promise back before it settles, so catch never sees the rejection and finally runs before the work is done. return await fixes both, and it is not slower.
# why?
Most online converters upload your data, show three ad banners, and ask for an email. This site doesn't. Nearly every tool here is a static page with a small script that runs in your browser, so your input never leaves your device. A few tools need a server because the browser physically can't do the job — and each one is labeled and spells out exactly what it does: the URL shortener stores your link so it can redirect, the DNS lookup only relays a query and keeps nothing. We add a free-tool backend only when there's no client-side way, and only while it stays free on Cloudflare's edge — those tools cost you $0, always. Pages are open-source and hosted on Cloudflare so they load fast from anywhere. A small set of clearly-marked Pro tools are paid with credits for heavy server work the browser physically can't do — they're opt-in and never gate or replace a free tool.