Free online developer tools that never see your data
72 browser-based tools for the things developers keep needing: formatting and validating JSON, converting JSON into TypeScript / Java / Go / Python types, Base64 and URL encoding, decoding JWTs, hashing, testing regexes, parsing cron expressions, converting timestamps. Everything runs locally — no sign-up, and nothing you paste leaves the page.
Parsing, conversion and hashing all happen in your browser. There is no backend endpoint that receives your input.
Pages are prerendered static HTML. No login, no install, no request to a server before the tool works.
Behaviour follows the actual specs for JSON, YAML and cron, and conversions that lose information say so instead of silently mangling your data.
JSON essentials
Re-indent minified or messy JSON with 2-space or 4-space indentation, catch syntax errors with exact line and column numbers, then copy or download the result.
Collapse multi-line JSON into a single compact line, with syntax still validated and the before-and-after byte size visible, for request bodies, log lines and message payloads.
Find out immediately whether a document is valid JSON, exactly where it breaks if it is not, and what the structure looks like once it parses.
Turn pseudo-JSON copied out of source code or logs — comments, single quotes, trailing commas, unquoted keys — into standard JSON that other languages will accept.
Turn JSON into an escaped string literal you can paste into source code, or decode an escaped blob from a log or database column back into readable JSON.
Decode \uXXXX sequences into readable characters, or encode accents, CJK, Cyrillic and emoji so a payload survives an ASCII-only pipeline.
Reorder keys at every nesting level so two payloads that differ only in field order become directly comparable, instead of producing a diff where every line changed.
Lay nested JSON out as a collapsible tree, search for a key or value, and copy the path to any node instead of counting braces to work out where a field lives.
Put two JSON documents side by side and see exactly which fields were added, removed or changed, after formatting and sorting away the noise of indentation and key order.
Pull the fields you need out of deeply nested JSON with one expression and watch the matches update as you type, instead of writing a throwaway extraction script.
NDJSON ↔ JSON array, both directions: line-numbered errors, tolerant skipping, logs-friendly.
Paste JSON, run jq expressions instantly; the everyday syntax is covered and unsupported parts say so.
Code & data conversion
Turn a JSON sample into export-ready TypeScript interfaces: nested objects become their own types, arrays become T[], and nulls fall back to any.
Turn JSON into Lombok @Data classes: nested objects become their own classes, snake_case keys become camelCase fields, and @JsonProperty keeps Jackson binding.
Generate Go structs with json tags from a JSON sample: numbers split into int and float64, nested objects become their own structs, and unknown shapes fall back to interface{}.
Turn a JSON sample into Pydantic BaseModel classes: typed fields, nested models written before their parents, and output that runs unchanged on Pydantic v1 and v2.
Two-way conversion between JSON and YAML: the YAML output uses 2-space indentation and keeps key order, and YAML input comes back as formatted JSON.
Convert both ways between JSON and XML: arrays become repeated tags, attributes come back as @_ keys, and the mapping rules are fixed in both directions.
Turn a JSON array into a CSV file you can open in a spreadsheet: the header is the union of every key, cells are quoted and escaped, and nested values become JSON text.
Codable structs with CodingKeys mappings, one struct per nested object — paste-ready.
Data classes with val fields, camelCase names and @JsonProperty mappings out of the box.
serde structs with derive macros, rename mappings, Vec arrays and i64/f64 dispatch.
POCOs with auto-properties, PascalCase names, JsonPropertyName mappings and List<T>.
Two-way Markdown/HTML conversion with a sandboxed live preview; paste rich text and get clean Markdown back.
Clause-per-line SQL beautifier with keyword-case control; string contents are sacred.
Tag-structure re-indentation with CDATA and comments preserved, plus a minifier.
Parse-and-reemit YAML formatting with selectable indent; errors point at line and column.
Encoding & hashing
Encode and decode Base64 for text and images, with UTF-8 handling, the URL-safe alphabet, Data URL support and file size readouts.
Encode and decode URLs and query strings, with both encodeURIComponent and encodeURI, a batch mode for many lines and a query parameter table.
Split a JWT into header, payload and signature, read the time claims as dates, and verify an HS256 signature locally so the secret never leaves the page.
Five digests at once for text or a file, output as hex or Base64, computed locally so the file never leaves your machine.
Escape and unescape HTML entities in three modes; unknown entities pass through instead of being dropped.
SM3 hash and SM4 encryption (ECB/CBC, PKCS#7) with a one-click standard-vector self-test; local and key-safe.
Drop a file to sniff and decode; encode text back into GBK and other legacy encodings — local, honest about loss.
AES-GCM/CBC text encryption with PBKDF2-derived keys and a self-describing ciphertext format.
Browser-local 2048/4096-bit RSA key pairs as standard PEM, downloadable.
Paste a Base32 secret for live TOTP codes, with verification and a migration QR.
RFC 4648 and Crockford Base32 with confusable-tolerant decoding and a byte hex view.
Bitcoin-alphabet Base58 plus short-link Base62, with leading zeros handled correctly.
Text tools
Compare two blocks of text or code line by line in a side-by-side view, ignoring whitespace or case when a config file throws up formatting noise.
Test any regular expression against real text with live highlighting, capture groups, a replacement preview and switchable flags.
Turn a cron expression into a plain-English sentence and the next 10 run times, with a field reference for 5-field and 6-field schedules.
Live character, word and paragraph counts plus platform length budgets as you type.
Split any URL into protocol, host, path segments and a query-param table with encoded/decoded pairs.
Turn curl into fetch / axios / requests / Go code, with the parsed request shown first.
Paste any style, get all eight naming conventions at once with per-row copy — acronyms and digits handled.
Calculators
Two-way conversion between Unix timestamps and dates, with automatic seconds / milliseconds detection, UTC, ISO 8601 and local readings, plus batch conversion and date arithmetic.
One moment across eight time zones, plus natural-day, weekday and duration differences.
Bin/oct/dec/hex conversion with prefix detection, plus a 32-bit bitwise calculator and bit view.
HEX/RGB/HSL/OKLCH conversion plus WCAG contrast checking with a live preview.
Seven unit families with one-typed-value-all-results tables; temperature and KB/KiB done right.
IP + prefix/mask → network, broadcast, usable range and subnet splitting, with an IPv6 inspector; local math.
Number → RMB amount in Chinese words per check-writing rules, plus reverse lookup with a round-trip check.
Generators
Generate up to 100 UUID v4 values with the browser CSPRNG, and check existing UUIDs for validity, version and v1 timestamp.
Generate high-entropy random passwords, Diceware passphrases, and numeric PINs using Web Crypto CSPRNG with real-time Shannon entropy and crack-time evaluation.
Batch-generate ULIDs and NanoIDs; parse ULIDs back to timestamps and UUID form; monotonic mode for DB keys.
Paste one example record, get N structurally identical records with realistic field values.
Files & media
Generate: turn text, URLs, Wi-Fi or contact payloads into a QR code with an optional logo, exported as PNG or SVG. Decode: drop, paste or capture a QR code and read it locally, nothing uploaded.
Parse and play raw PCM streams, WAV, MP3 and more with interactive waveforms, acoustic metrics, frame structure breakdown and hex data inspection.
Batch-compress images or convert between JPG / PNG / WebP with quality and size controls, all locally.
See the camera settings, timestamps and GPS coordinates inside a photo - and whether they should be stripped before sharing.
See the container structure, codec parameters and true bitrate of an MP4/M4A/MOV - and diagnose what breaks streaming.
One image in: favicon.ico, every PNG size, the Apple touch icon, a web manifest and the HTML snippet - as a ZIP.
Merge PDFs in order, extract a page range, or split every page into its own file - locally, without uploads.
Waveform preview with a two-slider selection; preview it, then export MP3 or lossless WAV — sample-accurate, local.
Text or logo watermarks, 9-grid or tiled, batch-packed as ZIP; local canvas compositing, nothing uploaded.
Render each PDF page to JPG/PNG at 1×–3× scale, single-page or full-ZIP export; local rendering.
Reference
Why these tools live in one place
The annoyances that slow developers down are usually small ones: a minified API response that needs to be expanded before you can read it, a documented example that no longer matches the real payload, hand-writing a dozen fields to turn a JSON sample into a typed struct, guessing whether a timestamp is in seconds or milliseconds. None of these is hard. But each one sends you hunting for a tool, pasting data into it, and wondering where that data just went.
Keeping these tools together, and holding two lines — usable instantly, and your data never leaves the browser — is the whole point of this site. They also hand off to each other: what you paste in the formatter is still there when you open the diff, tree view, JSONPath query or code converter, so you never paste twice.
About data safety
There is no backend. Every calculation ships as static files and runs in your browser, which means the API responses, tokens and file contents you paste never leave your machine — you can even disconnect from the network and keep using an open page. The trade-off is explicit: because there is no server, anything that needs one (live HTTP request testing, IP geolocation, document conversion) is out of scope here.
About this site
Display ads cover the domain and hosting costs. Ads never affect how a tool works, and the content you type into a tool is never associated with them. How data is handled, and the cookies ads may set, are described in the privacy policy; what this site is and how it is built is in the about page.