DevToolMate

Free online developer tools for JSON, encoding, security, text, time, SQL, web, color, and AI workflows. Every tool runs locally in your browser. Your data is not uploaded.

Categories

  • AI tools (5 tools)
  • Cron tools (4 tools)
  • Encoding tools (6 tools)
  • HTML/CSS/JS tools (31 tools)
  • JSON tools (14 tools)
  • Security tools (11 tools)
  • SQL tools (3 tools)
  • Text tools (12 tools)
  • Time tools (7 tools)

AI tools

  • Token Counter: Free token counter and content length calculator. Estimate prompt tokens and string length locally in your browser with character, word, and byte counts. No upload, no account.
  • Prompt Diff: Compare two prompts line by line in your browser. Free, no upload. Private, browser-based developer tool.
  • Embedding Cosine Similarity: Free cosine similarity calculator for vectors. Compute embedding similarity and angle locally in your browser with no upload, no account, no API calls.
  • Markdown to Plain Text: Strip Markdown formatting to plain text online for cleaner LLM prompts. Free, browser-local, no upload required. Privacy-first developer tool.
  • Context Budget Splitter: Split long text into character-budget chunks for LLM context windows. Free browser tool, no upload. Estimate tokens locally.

Cron tools

  • Cron Expression Generator: Free cron expression generator for Quartz, Spring, and crontab. Build 5-field cron job expressions locally in your browser with no upload or account.
  • Cron Expression Parser: Free cron job expression parser: decode cron expressions into plain language and field breakdown locally in your browser. No upload, no account, no execution.
  • Cron Expression Explainer: Free online cron expression generator and explainer. Understand cron job schedules in plain English instantly. Browser-local, no upload, no account.
  • Cron Validator: Validate cron job expressions online: check 5- or 6-field syntax, field ranges, and errors instantly. No upload, no account. Test before Kubernetes, GitHub Actions, or crontab.

Encoding tools

  • Base64 Encoder: Base64 encoder online: convert text to Base64 in your browser. Free, no upload, no account. Handles multiline, Unicode, and special characters locally.
  • Base64 Decoder: Free online base64 decoder. Decode base64 strings to UTF-8 text instantly in your browser with no upload, no account, and no server processing.
  • URL Encoder: Escape string online and percent-encode query parameters with URL Encoder. Encode reserved characters safely in your browser, no upload needed.
  • URL Decoder: Unescape percent-encoded URLs and query strings locally in your browser. Free URL decoder online, no upload, no account. Handles plus signs, Unicode, and form data.
  • HTML Entity Encoder: Escape string online free. Convert &, <, >, and quotes to HTML entities in your browser. No upload, no account, no server processing.
  • HTML Entity Decoder: Unescape named HTML entities online: decode &lt;, &gt;, &amp;, quotes to plain text in your browser. Free, local, no upload, no account.

HTML/CSS/JS tools

  • HTML Formatter: Format HTML online free with pretty-print indentation. Beautify minified markup in your browser, no upload, no account required.
  • HTML Minifier: Online HTML minifier - compress HTML in your browser by removing comments and whitespace. No upload, no account required. Runs locally.
  • CSS Formatter: Format and beautify CSS online in your browser. Pretty-print minified stylesheets with custom indentation. No upload, no account, privacy-first.
  • CSS Minifier: Free online CSS minifier - compress stylesheets by removing comments and whitespace. Runs locally in your browser, no upload, no account required.
  • JavaScript Formatter: Format JavaScript online in your browser with custom indentation. Free, no upload, no account. Pretty-print minified JS as text only - code never executed or stored.
  • JavaScript Minifier: Free JavaScript minifier that runs browser-local. Minify JS by removing comments and whitespace. No upload, no account, no code execution.
  • Color Picker: Free online color picker for HEX, RGB, HSL, HSV, and OKLCH. Pick a color and inspect all formats instantly in your browser. No upload, no account.
  • Color Converter: Free hex to rgba converter: Convert HEX, RGB, HSL, HSV, and approximate OKLCH instantly in your browser. No upload, no account, no data stored.
  • Complementary Colors: Complementary color generator: find opposite hues and evenly spaced palettes from any seed color in your browser. No upload, no account, runs locally.
  • Color Palette Generator: Free hex color palette generator using analogous, triadic, and tetradic color schemes. Build harmonious palettes from one seed color in your browser, no upload or account.
  • Tint and Shade Generator: Free colour shade generator. Create lighter tints and darker shades from any base color using HSL lightness steps. Copy HEX, RGB, HSL, HSV, OKLCH. Browser-local, no upload, no account.
  • Color Blindness Simulator: Simulate protanopia, deuteranopia, or tritanopia for one color. See how colorblind people perceive your design. Browser-local, no upload, free.
  • HEX to RGBA: Hex to rgba converter: paste HEX, RGB, or HSL and adjust alpha from 0 to 1 for instant rgba() output. Local browser processing, no upload.
  • Tailwind Palette Generator: Free shade generator for Tailwind. Generate a 50-950 color palette from one seed color locally in your browser. HEX, RGB, HSL, HSV, OKLCH. No upload, no account.
  • Random Accessible Palette: Generate random accessible color palettes with WCAG contrast checks. HEX, RGB, HSL, HSV, OKLCH formats. Browser-local, no upload.
  • CSS Gradient Generator: Free CSS gradient generator for linear-gradient backgrounds. Set angle 0-360deg, color stops in HEX/rgb/hsl, and preview live. Runs locally in your browser.
  • Box Shadow Generator: Free CSS box shadow generator with live preview. Adjust offset, blur, spread, color locally in your browser. No upload, no account required.
  • Border Radius Generator: Free border radius generator online. Create rounded corners CSS locally in your browser, set uniform or individual corner radii, preview live, copy CSS. No upload, no account.
  • rem to px Converter: Convert rem to px or px to rem with custom root font size. Enter 1.25rem, 3rem, or any value and get instant results in your browser - no upload, no account.
  • CSS Unit Converter: Free CSS unit converter: convert px, rem, em, vw, vh, % locally in your browser. Set root font size and viewport width. No upload, no account required.
  • Aspect Ratio Calculator: Free aspect ratio calculator for CSS aspect-ratio property. Enter 16:9 or pixel dimensions to get simplified ratios, CSS declarations, and responsive sizing, all in your browser, no upload.
  • CSS Specificity Calculator: CSS specificity calculator: score selectors as (a,b,c) tuples and compare them to debug cascade conflicts. Free, browser-local, no upload.
  • CSS Filter Generator: CSS filter online generator. Adjust blur, brightness, contrast, saturate, grayscale with live preview. Copy or download filter.css. Browser-local, no upload, no account.
  • Meta & OG Tags: Generate Open Graph and Twitter Card meta tags as escaped HTML text locally. Free browser tool, no upload, no account needed.
  • robots.txt Generator: Create robots.txt online free. Generate robots.txt files locally in your browser with user-agent, allow, disallow, and sitemap fields. No upload or account needed.
  • SVG to Data URI: Free SVG to data URI converter. Browser-local, no upload. Convert SVG to inline data:image/svg+xml URLs for CSS, img src, and webpack.
  • Image to Base64: Free image to base64 converter. Convert PNG, JPG, GIF, WebP to data URLs in your browser. No upload, no account.
  • Favicon Emoji Data URI: Convert emoji to SVG favicon data URI in your browser. Generate copy-ready link rel icon code locally, no upload or account needed.
  • HTML to Markdown: Format HTML online to Markdown instantly. Free browser-based converter, no upload needed. Convert HTML tags to Markdown locally, safe, private, no account.
  • Markdown to HTML: Convert Markdown to HTML online, free and locally in your browser. Escaped output displays as text, not live code. No upload, no account required.
  • Lorem Ipsum Generator: Generate placeholder Lorem Ipsum paragraphs locally in your browser. Free, no upload, no account. Privacy-first developer tool.

JSON tools

  • JSON Formatter: Online JSON formatter - beautify and format JSON in your browser with adjustable indentation and key sorting. Free, no upload, no account.
  • JSON Validator: Free JSON validator and linter online. Validate JSON syntax in your browser with line-level error messages. No upload, no account, runs locally.
  • JSON Minifier: Minify JSON online by removing whitespace in your browser. Free, no upload, no account. Compress JSON for APIs and storage instantly.
  • JSON Beautifier: Free JSON beautifier online - pretty print with indentation, sort keys, validate syntax. Runs locally in your browser, no upload, no account.
  • JSON to CSV: Convert JSON to CSV online in your browser. Transform JSON arrays into spreadsheet-ready CSV with proper escaping. No upload, no account, no server processing.
  • CSV to JSON: Convert CSV to JSON online, free and private. Handles quoted fields, duplicate headers, Python and JavaScript exports. Browser-local, no upload, no account.
  • JSON to YAML: Convert JSON to YAML online free, no upload. Browser-local converter for Docker Compose, Kubernetes, Helm, Swagger, and GitLab CI configs.
  • YAML to JSON: Convert YAML to JSON online free, no upload. Safe parsing in your browser for docker-compose, Kubernetes, OpenAPI specs. No account needed.
  • JSON Tree Viewer: Inspect JSON paths in a collapsible tree viewer. Explore nested objects and arrays in your browser without uploading. Free, no account, runs locally.
  • JSON Diff: Compare JSON files and spot differences online with canonical formatting and line-oriented diff. Free tool runs in your browser, no upload, no account.
  • JSON to TypeScript: Generate TypeScript interfaces from JSON samples free, online, in your browser. No upload. Customize root type name, infer arrays, quote keys.
  • JSONPath Query: Free jsonpath online tool to query JSON in your browser. Extract fields with dot notation, array indexes, and wildcards. No upload, no account, no server processing.
  • JSON Flatten: Flatten JSON online free with dotted keys. Convert nested objects and arrays to dot notation in your browser. No upload, no account, no server processing.
  • JSON Unflatten: Flatten JSON online then unflatten back to nested objects and arrays. Free browser tool, no upload, no account. Rebuild nested JSON locally.

Security tools

  • JWT Decoder: Decode JWT online and inspect bearer tokens locally in your browser. View header, payload, and OAuth 2.0 claims instantly. Free, no upload, no account.
  • JWT Header Viewer: Decode JWT header online in your browser. View alg, typ, and other header fields locally. Free, no upload, no account required.
  • JWT Payload Viewer: Decode JWT payload online free. View claims like sub, exp, iat in your browser. No upload, no account, no signature verification.
  • SHA-256 Hash Generator: Free online SHA-256 hash generator and calculator. Generate checksums instantly in your browser with no upload or account required.
  • SHA-512 Hash Generator: SHA512 online generator: free browser-based hash tool. Generate 128-character hex checksums locally with Web Crypto. No upload, no account required.
  • SHA-1 Hash Generator: Free SHA-1 encoder online. Generate SHA-1 hashes in your browser, convert to base64. No upload, no account, no server processing.
  • MD5 Hash Generator: Free random MD5 hash generator that runs locally in your browser. Hash random strings, tokens, and identifiers with no upload or account required. MD5 is not collision-resistant; use SHA-256 for new designs.
  • Hash Generator: Generate MD5, SHA1, SHA256, and SHA512 hashes online free in your browser. Encode text to SHA1 hex or compare all four digests instantly. No upload, no account.
  • UUID Generator: Generate random UUID v4 online in your browser. Bulk generate 1 to 10,000 UUIDs instantly with no upload, no account, no server processing.
  • UUID Validator: Free UUID and GUID validator: check valid UUIDs in RFC 4122 format, version/variant nibbles, bulk validate up to 10,000 IDs locally. No upload, no account.
  • Random String Generator: Generate random strings online in your browser with crypto.getRandomValues. Choose hex, alphanumeric, or URL-safe alphabets. Free, no upload, no account required.

SQL tools

  • SQL Formatter: Free SQL formatter online to beautify and pretty-print queries locally in your browser. Format SQL with readable indentation, no upload, no execution, no account needed.
  • SQL Minifier: Compress SQL queries by removing comments and whitespace. Free online SQL minifier runs locally in your browser, no upload, no account needed.
  • SQL Beautifier: Free SQL beautifier online. Format SQL queries in your browser with stable indentation. No upload, no account, no database execution.

Text tools

  • Regex Tester: Free regex tester online for JavaScript. Test patterns, see match indices and capture groups in your browser with no upload, no account required.
  • Text Diff: Free text diff online tool to compare two texts line by line in your browser. See added, removed, and unchanged lines instantly. No upload, no account.
  • String Length Calculator: String length online calculator: count characters, UTF-8 bytes, UTF-16 code units free. No upload, no account. Paste text to check byte length for APIs and databases.
  • Word Counter: Word counter online: count words, characters, and lines instantly in your browser. Free string length calculator. No upload, no account required.
  • Line Counter: Count lines in text online, including empty lines. Free browser-local line counter for logs, CSV, and code. No upload, no account needed.
  • Case Converter: Case converter online: convert text to uppercase, lowercase, title case, sentence case, snake_case, kebab-case, camelCase. Free, browser-local, no upload.
  • Remove Duplicate Lines: Remove duplicate lines online free. Deduplicate text while keeping first occurrence in order. Browser-based, no upload, no account needed.
  • Sort Lines: Order and sort lines alphabetically online with numeric-aware, case-insensitive comparison. Free browser tool, no upload, no account needed.
  • Trim Lines: Trim leading and trailing whitespace from each line locally. Preserves inner spaces and blank lines. Free, browser-based, no upload.
  • Escape String: Escape string online free - convert raw text to valid JSON string literals in your browser. Handles quotes, newlines, tabs, control characters. No upload, no account.
  • Unescape String: Unescape string online: convert JSON escape sequences back to raw text in your browser. Free, no upload, no account. Parse \n, \t, \" locally.
  • QR Code Generator: Free QR Code Generator: Create scannable QR codes as SVG & PNG locally in your browser. No upload, no API, no account. Privacy-first.

Time tools

  • Unix Timestamp Converter: Convert Unix timestamp to date online, free and browser-local. Handles seconds, milliseconds, ISO 8601, negative epochs, and Discord timestamps. No upload, no account.
  • Timestamp Converter: Convert Unix timestamp to date online in your browser. Free tool outputs seconds, milliseconds, ISO 8601 UTC, and local time. No upload, no account, no server processing.
  • Unix Timestamp Generator: Generate current Unix timestamp online instantly from your device clock. Free browser tool shows live epoch seconds, milliseconds, ISO 8601 UTC, and local time. No upload, no account.
  • Date to Unix Timestamp: Convert date to Unix timestamp online. Paste ISO 8601 strings or numeric timestamps; get Unix seconds and milliseconds instantly. Free, browser-local, no upload.
  • Unix Timestamp to Date: Convert Unix timestamp to date online instantly. Auto-detects seconds vs milliseconds. Get ISO 8601, UTC, and local time. Browser-local, no upload.
  • ISO 8601 Converter: ISO 8601 converter: transform Unix timestamps and dates to UTC format online. Browser-local, no upload, no account. Handles seconds, milliseconds, RFC 3339.
  • Timezone Converter: Convert any instant between 400+ IANA time zones in your browser. Paste ISO 8601 or unix timestamp to see UTC offset and local time. Free, no upload, no account.

Engineering case studies

  • The Internal Wiki RAG Pilot: Chunking, Tokens, and SEO Without Sending Data to SaaS: A platform team pilots retrieval-augmented search over an internal wiki, chunking Markdown locally, budgeting tokens, diffing prompts, scoring embedding similarity, and scaffolding robots.txt and meta tags without pasting proprietary content into third-party tools.
  • When the Brand Refresh Met the Tailwind Config: Reconciling Figma Hex with Accessible Production CSS: A design-system lead inherits seventeen new brand swatches from Figma and forty-seven components that still reference the old palette, using local color, palette, and CSS generator tools to ship accessible tokens, gradients, and shadows without uploading brand assets to a third-party API.
  • Cron Expressions Explained: When the Invoice Job Fired Twice on Spring-Forward Sunday: A weekly billing CronJob and a legacy UTC EventBridge rule both thought they owned 2:00 AM Eastern. On US spring-forward Sunday the offsets diverged and customers were invoiced twice. Walk through cron fields, Kubernetes timeZone semantics, and four local DevToolMate tools to validate before the next DST boundary.
  • When OAuth Breaks on a Double-Encoded Redirect: Tracing Bytes Through UTF-8, Base64, URL, and HTML: A production OAuth callback failed because a redirect URL was encoded twice. Follow the incident from pager alert to root cause through UTF-8 bytes, percent-encoding, Base64, HTML entities, JSON escapes, and data URIs.
  • When a Legacy Admin Export Arrived as One Line: Formatting HTML, CSS, and JavaScript as Text: A decommissioned admin panel dumped minified HTML, CSS, and JavaScript into a migration ticket. Follow how the team formatted markup as text, converted fragments to Markdown for docs, and kept every byte local, without executing a single script tag.
  • When Checkout Returns 200 but Totals Lie: Debugging a Silent JSON Contract Break: A payments team traces wrong checkout totals through microservices, using JSON format, validate, convert, diff, and query tools to find a silent schema drift that HTTP status codes never surfaced.
  • Security Incident Hour One: Decode JWTs and Hash Indicators Locally Without Third-Party Debuggers: Follow an on-call engineer through the first hour of a token-related alert, decode JWT headers and claims, fingerprint IOCs with SHA and MD5, and validate request IDs entirely on your machine, with no uploads to external debuggers.
  • When a 600-Line Migration PR Dies in Review: Readability vs Minified Deploy Artifacts: A platform team rejects a massive schema migration because the SQL arrived as a minified deploy artifact nobody could review. Follow how local format, beautify, and minify tools separate source-of-truth readability from production transport, without executing a single statement.
  • On-Call Log Forensics: Regex, Dedupe, and QR Workflows on a 2GB File, All Local: Pager at 2 a.m., a two-gigabyte log export, and a policy that forbids uploading customer data to random websites. Walk through ten DevToolMate text tools for regex testing, diffs, counts, line cleanup, and QR codes during incident triage entirely in your browser.
  • Timestamps and Timezones: Fixing the São Paulo Billing Hour and Mastering UTC, Unix, and IANA Zones: When a billing dashboard shows São Paulo renewals one hour early, the database is usually right and the display layer is wrong. Walk through UTC storage, epoch seconds versus milliseconds, ISO 8601, and IANA timezone conversion with seven local-first DevToolMate tools.

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