# tool4.dev > Fast, privacy-first developer and engineering tools that run in the browser. Tool inputs stay in the browser unless a page explicitly says otherwise. Each link below opens the canonical human-readable page with usage guidance, limitations, privacy details, and common questions. ## Start here - [All tools](https://tool4.dev/tools): Browse the complete tool catalogue. - [About tool4.dev](https://tool4.dev/about): How the site is designed and why local processing is the default. - [Contact](https://tool4.dev/contact): Maintainer contact and privacy-safe bug reporting. ## Data - [Data tools](https://tool4.dev/tools/data): Validate, compare, convert, and inspect structured developer data. - [JSON Stringify & Unstringify](https://tool4.dev/tools/json-stringify): Turn JSON into a JSON string literal or decode a stringified JSON document locally. - [Structured Data Tree Viewer](https://tool4.dev/tools/json-viewer): Explore JSON, YAML, TOML, and XML as a searchable, collapsible tree in your browser. - [JSON, YAML & CSV Converter](https://tool4.dev/tools/json-yaml-csv): Convert JSON, YAML, and CSV locally with inferred input and explicit output format. - [JSON to Types](https://tool4.dev/tools/json-to-types): Infer TypeScript, Go, or Python data models from a JSON sample locally. - [JSON to JSON Schema](https://tool4.dev/tools/json-schema-generator): Infer a Draft 2020-12 JSON Schema from representative JSON without uploading it. - [JSON Schema Validator](https://tool4.dev/tools/json-schema-validator): Validate JSON against a local Draft 2020-12 schema and inspect every failing path. - [JSON Patch & Merge Patch Tester](https://tool4.dev/tools/json-patch-tester): Apply RFC 6902 JSON Patch or RFC 7396 Merge Patch locally and inspect the resulting document. - [.env.example to Typed Config Loader](https://tool4.dev/tools/env-config-loader): Generate a validated TypeScript, Go, or Python configuration loader from .env.example. - [JSON Diff](https://tool4.dev/tools/json-diff): Compare two JSON documents and see exactly what changed in your browser. - [Text Diff](https://tool4.dev/tools/text-diff): Compare source, configuration, logs, or arbitrary text with focused line-by-line changes. - [.env File Diff](https://tool4.dev/tools/env-diff): Compare two .env files by key. Values stay masked until you reveal them, and nothing is uploaded. - [Regex Tester](https://tool4.dev/tools/regex-tester): Test a JavaScript regular expression against your text, with every match, capture group, and replacement shown locally. - [HL7 v2 Capture Inspector](https://tool4.dev/tools/hl7-v2-inspector): Inspect, filter, and correlate HL7 v2 messages and acknowledgments locally in your browser. - [HL7 v2 Message Diff](https://tool4.dev/tools/hl7-v2-diff): Compare two HL7 messages by field, component, repetition, and subcomponent locally. - [Color Picker & Converter](https://tool4.dev/tools/color-converter): Pick a color or paste any CSS color value and convert it between common, perceptual, and modern color spaces locally. - [Color Contrast Checker](https://tool4.dev/tools/color-contrast): Check WCAG contrast ratios for foreground and background colors, including transparency. - [XPath Tester](https://tool4.dev/tools/xpath-tester): Evaluate XPath 1.0 expressions against XML locally and inspect nodes, values, or paths. - [JSONPath Tester](https://tool4.dev/tools/jsonpath-tester): Evaluate JSONPath expressions against local JSON and inspect every matched path and value. - [SemVer Comparator & Range Tester](https://tool4.dev/tools/semver-range-tester): Compare strict semantic versions and test them against npm-style ranges locally. ## Formatters - [Formatters tools](https://tool4.dev/tools/formatters): Beautify and validate source documents locally without executing or uploading them. - [JSON Formatter & Validator](https://tool4.dev/tools/json-formatter): Format, minify, and validate JSON directly in your browser. - [XML Formatter & Validator](https://tool4.dev/tools/xml-formatter): Format and validate XML locally without fetching external entities. - [SQL Formatter](https://tool4.dev/tools/sql-formatter): Format SQL queries locally while preserving strings, comments, and parameters. - [YAML Formatter](https://tool4.dev/tools/yaml-formatter): Format and validate YAML locally while retaining YAML-specific syntax. - [JavaScript Formatter](https://tool4.dev/tools/javascript-formatter): Format and compact modern JavaScript locally without executing it. - [Reddit Text Formatter](https://tool4.dev/tools/reddit-text-formatter): Draft desktop Reddit Markdown or Discord text with a local preview and character counter. - [TOML Formatter & Validator](https://tool4.dev/tools/toml-formatter): Parse and format TOML 1.0 locally with explicit syntax errors. - [CSS Formatter & Validator](https://tool4.dev/tools/css-formatter): Format and validate modern CSS locally while preserving strings, comments, URLs, and calc expressions. - [LaTeX Equation Editor](https://tool4.dev/tools/latex-equation-editor): Write LaTeX equations with insertion helpers, a live preview, and copy-ready wrappers. ## Encoding - [Encoding tools](https://tool4.dev/tools/encoding): Encode, decode, and transform everyday developer text safely in your browser. - [Base64 Encode & Decode](https://tool4.dev/tools/base64): Encode text to Base64 or decode Base64 strings directly in your browser. - [URL Encoder & Decoder](https://tool4.dev/tools/url-encoder): Encode or decode URL components locally without exposing query data to the server. - [HTML Entity Reference](https://tool4.dev/tools/html-entities): Search every HTML named character reference and copy its forms locally. - [Unicode & Emoji Reference](https://tool4.dev/tools/unicode-emoji): Search thousands of Unicode symbols and every emoji with copyable code points and UTF-8 forms. - [Punycode / IDN Converter](https://tool4.dev/tools/punycode): Convert internationalized domain names between Unicode and ASCII Punycode locally. - [Number Base Converter & Bit Inspector](https://tool4.dev/tools/number-base-converter): Inspect binary, octal, decimal, hexadecimal, signed values, byte order, bitwise operations, floats, and characters. ## Files - [Files tools](https://tool4.dev/tools/files): Convert and inspect local images, documents, spreadsheets, and other files without uploading them. - [SVG Viewer & Editor](https://tool4.dev/tools/svg-viewer): Inspect, format, and preview SVG source locally without executing it. - [Image Converter](https://tool4.dev/tools/image-converter): Convert and resize PNG, JPEG, and WebP images locally with explicit quality and transparency handling. - [SVG Converter](https://tool4.dev/tools/svg-converter): Convert validated SVG source to PNG, JPEG, or WebP locally at exact pixel dimensions. - [Favicon Converter](https://tool4.dev/tools/favicon-converter): Build a real multi-size ICO and modern favicon ZIP package from one local image. - [Markdown Converter](https://tool4.dev/tools/markdown-converter): Convert GitHub Flavored Markdown and sanitized HTML locally, with a safe rendered preview. - [Spreadsheet Converter](https://tool4.dev/tools/spreadsheet-converter): Convert CSV, TSV, XLSX, and tabular JSON files locally with explicit sheet handling and a bounded preview. - [PDF Toolkit](https://tool4.dev/tools/pdf-toolkit): Merge, extract, reorder, rotate, remove, and optionally shrink PDF pages locally in one bounded workspace. - [Images to PDF](https://tool4.dev/tools/images-to-pdf): Arrange PNG, JPEG, and WebP images into a locally generated PDF with explicit page sizing and fit. - [PDF to Images](https://tool4.dev/tools/pdf-to-images): Render selected PDF pages to PNG or JPEG locally at an honest 1×, 2×, or 3× scale. - [Glob Pattern Tester](https://tool4.dev/tools/glob-tester): Test minimatch glob patterns and ordered exclusions against a local list of paths. - [3D Animation to Sprite Sheet](https://tool4.dev/tools/3d-animation-to-sprite-sheet): Render a rigged FBX or GLB character into a PNG sprite atlas with optional frame metadata entirely in the browser. - [Skeletal Mesh Retargeter](https://tool4.dev/tools/skeletal-mesh-retargeter): Rebuild a binary FBX mesh hierarchy with UE5, Unity-style, Mixamo, or custom bone names and download it locally. - [FBX Asset Repairer](https://tool4.dev/tools/fbx-asset-repairer): Repair broken FBX texture paths across an asset pack and download a portable ZIP locally. - [Spritesheet Slicer](https://tool4.dev/tools/spritesheet-slicer): Slice a regular PNG spritesheet into individual frames, preview playback, and download a local ZIP with frame coordinates. - [EXIF Metadata Inspector](https://tool4.dev/tools/exif-inspector): Read photo EXIF metadata locally: camera settings, timestamps, GPS coordinates, orientation, and recorded authorship. - [3D Asset Inspector](https://tool4.dev/tools/3d-asset-inspector): Inspect FBX or GLB meshes, materials, texture references, bones, and embedded animation clips without uploading the asset. ## Security - [Security tools](https://tool4.dev/tools/security): Inspect and work with security-related developer data locally. - [JWT Decoder](https://tool4.dev/tools/jwt-decoder): Decode JWT headers and payloads, and verify HS256 signatures, without sending your token or key to a server. - [PEM & X.509 Certificate Inspector](https://tool4.dev/tools/certificate-inspector): Inspect PEM or DER X.509 certificate identity, validity, names, keys, and fingerprints locally. - [SSH Public Key Inspector](https://tool4.dev/tools/ssh-public-key-inspector): Decode OpenSSH public keys, fingerprints, comments, and authorized_keys options locally. - [HMAC Generator & Verifier](https://tool4.dev/tools/hmac-generator): Compute and verify HMAC-SHA256, SHA-384, and SHA-512 signatures locally. Your payload and secret never leave the browser. - [Hash Generator](https://tool4.dev/tools/hash-generator): Generate SHA-256, SHA-384, or SHA-512 hashes locally for text or files, with optional digest verification. - [Content Security Policy Inspector & Builder](https://tool4.dev/tools/csp-inspector-builder): Parse, normalize, and review Content Security Policy directives with a local restrictive baseline. - [chmod & Unix Permissions Calculator](https://tool4.dev/tools/chmod-calculator): Translate Unix file permissions between octal, symbolic, and chmod command forms. ## Time - [Time tools](https://tool4.dev/tools/time): Convert and inspect timestamps and dates in the browser. - [Unix Timestamp Converter](https://tool4.dev/tools/unix-timestamp): Convert Unix timestamps and ISO dates locally in your browser. - [Cron Parser & Explainer](https://tool4.dev/tools/cron-parser): Explain five-field cron expressions and calculate upcoming runs locally. - [Cron Schedule Builder](https://tool4.dev/tools/cron-builder): Build standard five-field Unix cron schedules from friendly presets or custom fields. ## Generators - [Generators tools](https://tool4.dev/tools/generators): Produce the config files, templates, and values you would otherwise write from memory, deterministically and in your browser. - [UUID Generator](https://tool4.dev/tools/uuid-generator): Generate random UUID v4 values locally without sending them anywhere. - [Random Token Generator](https://tool4.dev/tools/random-token-generator): Generate cryptographically secure random tokens locally in your browser. - [Nginx Config Generator](https://tool4.dev/tools/nginx-config-generator): Generate an nginx server block for a reverse proxy or a static site, including the directives that belong in the http block. - [systemd Service Generator](https://tool4.dev/tools/systemd-service-generator): Write a complete systemd .service file from a few fields, including the directives that only work in pairs. - [.env Template Generator](https://tool4.dev/tools/env-template-generator): Generate a starter .env for the services you use, with conventional names and working local defaults. - [.gitignore Generator](https://tool4.dev/tools/gitignore-generator): Build a .gitignore from maintained fragments for your languages, frameworks, editors, and tooling. - [.env.example Sanitizer](https://tool4.dev/tools/env-example-sanitizer): Turn a real .env into the .env.example you can commit, with every value emptied unless a stated rule keeps it. - [Docker Run to Compose Converter](https://tool4.dev/tools/docker-run-to-compose): Turn a docker run command into a Compose service, with every flag it cannot translate reported. - [robots.txt Generator](https://tool4.dev/tools/robots-txt-generator): Generate a deterministic robots.txt starter file from readable local rules. - [QR Code Generator](https://tool4.dev/tools/qr-code-generator): Generate QR codes for text, links, contact details, Wi-Fi, and messages in your browser. - [Code Snippet Image Generator](https://tool4.dev/tools/code-snippet-image): Turn source code into a polished JPG or standalone HTML card locally. - [Color Harmony Generator](https://tool4.dev/tools/color-harmony): Pick a base color and generate complementary, analogous, triadic, split-complementary, tetradic, square, and monochromatic palettes locally. - [ULID Generator & Inspector](https://tool4.dev/tools/ulid): Generate cryptographically random ULIDs and inspect their timestamp and random components locally. ## HTTP & APIs - [HTTP & APIs tools](https://tool4.dev/tools/http-apis): Build, inspect, convert, and understand HTTP requests, responses, APIs, headers, and browser network data. - [URL & Query String Inspector](https://tool4.dev/tools/url-inspector): Break a URL into its parts and decode every query parameter locally, with credentials in the query string flagged. - [cURL Converter & Explainer](https://tool4.dev/tools/curl-to-code): Read what a curl command actually does, then convert it to JavaScript, Python, Go, Java, C#, PHP, Ruby, or Rust, in your browser. - [HTTP Request Builder](https://tool4.dev/tools/http-request-builder): Build an HTTP request locally and generate equivalent cURL, fetch, Python, or Go code without sending it. - [HTTP Header Inspector](https://tool4.dev/tools/http-header-inspector): Parse raw HTTP request or response headers locally and inspect repeated fields, caching, security, and CORS signals. - [HTTP Status Explorer](https://tool4.dev/tools/http-status-explorer): Search a canonical reference of HTTP status codes by number, family, and meaning entirely in your browser. - [HAR Inspector](https://tool4.dev/tools/har-inspector): Open a browser HAR file locally to summarize requests, timings, sizes, and response details without uploading the archive. - [User-Agent Parser](https://tool4.dev/tools/user-agent-parser): Parse a browser or client User-Agent string into readable local fields. - [OpenAPI Change Inspector](https://tool4.dev/tools/openapi-change-inspector): Compare two OpenAPI documents locally and review removed operations, newly required inputs, and other contract changes. ## Networking - [Networking tools](https://tool4.dev/tools/networking): Inspect DNS, calculate networks and subnets, and work with IP-level developer data. - [CIDR Calculator](https://tool4.dev/tools/cidr-calculator): Calculate IPv4 network, broadcast, mask, and usable address ranges locally. - [SPF & DMARC Record Explainer](https://tool4.dev/tools/dns-record-explainer): Explain an SPF or DMARC record term by term and flag what will not work. - [MAC Address Tool](https://tool4.dev/tools/mac-address): Convert MAC notations, read the assignment bits, and derive the EUI-64 and link-local address. - [Well-Known Ports Reference](https://tool4.dev/tools/port-reference): Search common TCP and UDP ports, what listens there, and the ones they are confused with. - [Subnet Planner](https://tool4.dev/tools/subnet-planner): Divide a block into subnets by host count, around the allocations you already have. - [IPv6 Address Tool](https://tool4.dev/tools/ipv6-tool): Expand, compress, and inspect IPv6 addresses, prefixes, and reverse DNS names. - [IP Range to CIDR Converter](https://tool4.dev/tools/ip-range-converter): Convert address ranges to CIDR blocks and back, aggregate blocks, and find overlaps. ## Electronics - [Electronics tools](https://tool4.dev/tools/electronics): Decode component markings, convert engineering units, and run transparent bench-scale circuit calculations. - [Resistor Code Calculator](https://tool4.dev/tools/resistor-code-calculator): Decode and encode resistor colour bands and common SMD markings. - [Ohm's Law & Power Calculator](https://tool4.dev/tools/ohms-law-calculator): Solve voltage, current, resistance, and power from any two known values. - [Voltage Divider Calculator](https://tool4.dev/tools/voltage-divider-calculator): Calculate loaded or unloaded divider voltage, currents, impedance, and power. - [Series & Parallel Resistor Calculator](https://tool4.dev/tools/resistor-network-calculator): Total a resistor list in series or parallel with tolerance and power results. - [LED Resistor Calculator](https://tool4.dev/tools/led-resistor-calculator): Choose the next preferred LED current-limiting resistor and inspect branch power. - [RC Time Constant & Filter Calculator](https://tool4.dev/tools/rc-calculator): Calculate RC time constant, filter cutoff, and charge/discharge thresholds. - [Engineering Unit Converter](https://tool4.dev/tools/unit-converter): Convert compatible mechanical, electrical, thermal, and data units with guided unit pickers. ## Optional - [Privacy](https://tool4.dev/privacy): How page requests, local input, and anonymous aggregate usage are handled. - [Terms](https://tool4.dev/terms): Terms for using the site. - [XML sitemap](https://tool4.dev/sitemap.xml): Canonical indexable URLs for search crawlers.