“I use ToolMono's JSON Formatter every single day at work. It's faster than anything else and my data never leaves my machine — that's non-negotiable for me.”
Developer Utility PlatformUpdated August 2026
Every tool you need. Right in your browser.
ToolMono is a blazing-fast developer utility platform. Format JSON, encode Base64, generate UUIDs, test regexes — all offline, all instant, zero tracking.
- Tools Available
- 76+
- Instant Search
- ⌘K
- Privacy
- 100% Local
- Avg TTFB
- <50ms
Featured Tools
The most popular utilities in one place
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Student Attendance Calculator
Calculate your attendance percentage, find how many classes you can miss, and see how many classes you need to attend to reach 75%, 80%, or any target.
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Markdown Table Generator
Create and edit Markdown tables online. Paste CSV, TSV, Excel or Google Sheets data, import Markdown, preview the result, align columns and copy clean GitHub-compatible Markdown.
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HTTP Status Code Reference & Lookup
Look up HTTP status codes by number or meaning. Understand 1xx–5xx responses, common causes, API usage, retry guidance, examples, RFC references and related codes.
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User-Agent Parser & Analyzer
Parse and analyze User-Agent strings online. Identify browser, version, operating system, device, rendering engine, CPU hints, bots, and Client Hints with batch parsing and JSON/CSV export.
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Cron Expression Generator & Validator
Build, validate and understand cron expressions online. Generate cron schedules visually, preview upcoming runs, test time zones and check Unix, Quartz and cloud scheduler syntax.
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Robots.txt Validator & Tester
Validate and test robots.txt files online. Check syntax, Allow/Disallow rules, Googlebot access, URL crawlability, sitemaps, AI crawlers, and SEO issues with exact winning-rule explanations.
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Dockerfile Linter & Analyzer
Analyze Dockerfiles for syntax errors, security risks, Docker best practices, image optimization opportunities, and build-caching improvements directly in your browser.
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HAR File Analyzer
Analyze HTTP Archive (HAR) files online to inspect network requests, response times, status codes, payload sizes, redirects, headers, and performance waterfalls directly in your browser.
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CORS Tester & Debugger
Test CORS configuration online, diagnose browser cross-origin errors, inspect CORS headers, test preflight OPTIONS requests, and get actionable server fix recommendations.
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HTTP Headers Analyzer
Analyze HTTP response headers online, audit security headers (CSP, HSTS, CORS), inspect cookies, detect information disclosure, and review caching policies.
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.env Validator & Environment Variable Comparator
Validate .env files, detect syntax errors, duplicate keys, empty values, potential secrets, compare environments, find missing variables, and review configuration drift.
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GraphQL Response Analyzer
Analyze GraphQL API responses online. Inspect data, errors, response paths, null values, structure, and response statistics with a privacy-first browser-based analyzer.
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GraphQL Playground & Query Tester
Test GraphQL APIs online with an interactive query editor, variables, headers, schema introspection, documentation explorer, response viewer, and GraphQL error debugging.
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JSON Schema Diff & Breaking Change Detector
Compare two JSON Schema versions and identify added, removed, and modified fields, type changes, constraint changes, required-field changes, and potential breaking changes.
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JSON Schema Validator
Validate JSON data against a JSON Schema online with detailed errors, JSON paths, draft detection, and browser-based processing.
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OpenAPI Example Request Generator
Generate ready-to-use API requests from OpenAPI and Swagger specifications. Select an endpoint, configure parameters and authentication, and instantly generate cURL, JavaScript Fetch, Axios, Python Requests, Node.js, and Raw HTTP examples.
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OpenAPI Diff Checker
Compare two OpenAPI or Swagger specifications online and detect breaking changes instantly. Compare endpoints, parameters, request bodies, response schemas, and security requirements in your browser.
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OpenAPI Validator Online
Validate, lint, and audit OpenAPI 3.2, 3.1, 3.0 and Swagger 2.0 specifications in JSON or YAML. Detect syntax errors, broken $ref pointers, path issues, security vulnerabilities, and API design warnings in your browser.
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JKS Viewer Online
Open and inspect Java KeyStore (JKS), PKCS12, PFX and JCEKS files directly in your browser.
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Webhook Tester – Free Tool to Inspect & Debug Webhooks Online
Generate a free temporary webhook URL to capture, inspect, and debug incoming HTTP payloads, headers, and JSON in real time. Replay requests instantly.
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Open Graph Checker & Social Media Preview Tool | Debug OG Tags
Instantly preview how your link looks on Facebook, Twitter, LinkedIn, and WhatsApp. Debug missing Open Graph tags, validate images, and fix your social media metadata with our professional-grade Open Graph Checker.
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Mermaid Editor – Create & Preview Mermaid Diagrams Online
Write, edit, and live-preview Mermaid.js diagrams directly in your browser. A fast, free, and private online Mermaid editor with instant PNG and SVG export.
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Postman to OpenAPI Converter
Convert your Postman Collection (JSON v2.0/2.1) to OpenAPI 3.0/3.1 specs instantly. Browser-based, secure, and free. No login required.
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Tailwind to Inline CSS Converter (HTML Email Ready)
Convert Tailwind CSS classes to inline style attributes instantly. Free online HTML email inliner with Tailwind v3 & v4 support, responsive fallbacks, and live preview.
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IP Subnet Calculator – CIDR, Subnet Mask & Host Range
Free online IP subnet calculator. Calculate CIDR notation, subnet masks, network addresses, broadcast ranges, usable hosts, and wildcard masks instantly.
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Parquet Viewer Online - Free In-Browser Parquet File Reader & SQL Explorer
View, inspect, and query Apache Parquet files online instantly in your browser. 100% private local processing using WebAssembly. View schemas, metadata, and export to CSV or JSON.
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PEM Certificate Decoder Online - Decode X.509 & SSL Certs | ToolMono
Free, 100% client-side PEM Certificate Decoder. Inspect X.509 fields, SANs, validity dates, fingerprints, and issuer details instantly in your browser.
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cURL to Code Converter: Instant In-Browser Translation
Convert cURL commands and browser DevTools requests into clean, idiomatic code for JavaScript, Python, Node.js, Go, and PHP. 100% client-side with zero server uploads.
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Numerical Methods Calculator
Interactive engineering workspace for Bisection, Newton-Raphson, Secant, Simpson's, Gaussian Elimination, and RK4.
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Docker Compose Visualizer
Visualize Docker Compose files as interactive service dependency graphs and architecture diagrams. Inspect networks, volumes, ports, and dependencies directly in your browser.
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OpenAPI Mock Generator
Generate realistic mock API responses from OpenAPI and Swagger specifications. Select an endpoint and response status, resolve schemas and $ref references, customize mock data, and export ready-to-use mock fixtures or server code entirely in your browser.
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Prompt Token Calculator
Count AI and LLM tokens in prompts, code, JSON, and text. Compare token usage by supported encodings with browser-based processing and no prompt uploads.
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AI.txt Validator
Validate AI.txt syntax, directives, and policy rules directly in your browser. Find line-level errors, review compatibility warnings, and generate a clean AI.txt file.
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PDF Tools Online
Use free online PDF tools to merge, split, compress, convert, edit, sign, and organize PDF files. Fast browser-based utilities with no installation required.
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Text Case Converter
Convert text online to UPPERCASE, lowercase, Title Case, Sentence case, Capitalized Case, Toggle Case, camelCase, snake_case and more.
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Text Compare
Compare two texts online and find differences instantly. Highlight changes line-by-line, word-by-word, or character-by-character with a fast browser-based diff checker.
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JSON Diff Checker
Compare two JSON files or objects online and find structural differences instantly. Detect added, removed, and modified values with nested key paths in your browser.
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Project Diff Viewer & Folder Comparison Tool
Compare two project folders, directories, or ZIP files online. Find added, removed, and modified files and inspect side-by-side content differences directly in your browser.
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Word Counter Online
Free word and character counter for essays, blogs, students, SEO, social media and everyday writing.
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JSON Formatter
Free online JSON formatter, beautifier, and validator. Format, indent, minify, and inspect JSON with real-time syntax error detection in your browser. 100% client-side.
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SQL Formatter
Free online SQL formatter and beautifier. Format, indent, and clean up SQL queries instantly in your browser. Supports MySQL, PostgreSQL, T-SQL, and Oracle.
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Regex Tester Online
Test JavaScript regular expressions with live match highlighting, capture-group inspection, flags, and replacement preview. 100% client-side privacy.
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SQL Query Analyzer Online
Inspect SQL statement structure, detect anti-patterns, evaluate query complexity, and generate plain-English summaries directly in your browser.
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JSON to CSV Converter
Convert JSON to CSV online with support for arrays, nested objects, custom delimiters and Excel-friendly CSV output. Fast browser-based conversion.
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CSV to JSON Converter
Convert CSV to JSON online with file upload, custom delimiters, smart type inference, dot notation unflattening, and JSON preview. 100% client-side conversion.
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Excel to JSON Converter
Convert Excel files (.xlsx, .xls, .xlsm) to JSON online with multi-worksheet support, raw primitive casting, and JSON preview. 100% client-side conversion.
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JSON to Excel Converter
Convert JSON data to Excel (.xlsx) online. Flatten nested objects, preview spreadsheet data, and download an Excel workbook directly from your browser.
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Hash Generator
Generate hashes and file checksums locally in your browser. Compare digests, copy results, and use MD5, SHA-1, SHA-2, SHA-3, BLAKE2, and supported HMAC algorithms.
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JWT Decoder Online
Decode JWT tokens instantly in your browser. Inspect headers, payload claims, verify signatures, convert timestamps, and debug JWTs securely with 100% client-side processing.
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Online UUID & GUID Generator
Generate secure UUID v4 and time-ordered UUID v7 identifiers online. Create single or bulk UUIDs with formatting controls, GUID support, and client-side Web Crypto generation.
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Base64 Encoder Decoder
Free, 100% client-side Base64 encoder and decoder. Convert text, strings, and data to Base64 or Base64URL instantly with UTF-8 support, padding controls, and client-side processing.
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Color Converter
Free online color converter. Convert HEX, RGB, RGBA, HSL, CMYK, LAB, OKLCH & CSS color codes instantly with live preview, WCAG contrast checker & developer exports.
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Secure Password Generator
Generate strong random passwords and memorable passphrases instantly in your browser. Customize length, characters, and options with browser-based cryptographic randomness.
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Package.json Viewer & Explorer
Free online package.json viewer and explorer. Inspect npm dependencies, scripts, metadata, entry points, and Node.js configuration directly in your browser.
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Requirements.txt Analyzer & Syntax Checker
Parse and inspect requirements.txt files online. Analyze Python dependencies, version specifiers, extras, markers, and pinning directly in your browser.
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Dependency Graph & Tree Viewer
Visualize NPM and project dependencies online. Explore package.json and lockfile dependency trees, trace transitive packages, and inspect dependency relationships directly in your browser.
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NPM Dependency License Checker
Check licenses for NPM and Node.js dependencies online. Inspect package versions, license identifiers, direct and transitive dependencies, and export a license inventory when supported.
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Online HAR File Sanitizer & Sensitive Data Redactor
Sanitize HAR files online by redacting cookies, Authorization headers, Bearer tokens, and other sensitive data directly in your browser.
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JSON Transformer
Free online multi-engine JSON transformer. Filter, reshape, map, and restructure complex JSON payloads using JavaScript, jq, JSONPath, and Jolt specifications with 100% client-side Web Worker execution, live preview, and Monaco editors.
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Local Background Remover
Remove solid-color backgrounds entirely inside your browser. No uploads, no login, unlimited use.
Popular Tools
The most frequently used utilities by developers
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Text Compare
Compare two texts online and find differences instantly. Highlight changes line-by-line, word-by-word, or character-by-character with a fast browser-based diff checker.
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JSON Formatter
Free online JSON formatter, beautifier, and validator. Format, indent, minify, and inspect JSON with real-time syntax error detection in your browser. 100% client-side.
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Regex Tester Online
Test JavaScript regular expressions with live match highlighting, capture-group inspection, flags, and replacement preview. 100% client-side privacy.
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Base64 Encoder Decoder
Free, 100% client-side Base64 encoder and decoder. Convert text, strings, and data to Base64 or Base64URL instantly with UTF-8 support, padding controls, and client-side processing.
Trusted by Developers
Thousands of engineers, data scientists, and security pros use ToolMono daily.
“The JWT Decoder saved me hours of debugging auth issues. I can see the token claims instantly without installing anything. Genuinely impressed.”
“Finally a Base64 tool I can use on sensitive payloads. Client-side only, zero uploads, works offline. ToolMono is now my go-to bookmark.”
“The Regex Tester with code generation for 8 languages is a massive time saver. I paste a pattern once and get copy-ready snippets for Python, Go, and JS simultaneously.”
“ToolMono is the only dev tool suite I've recommended to my entire team. Fast, private, beautiful dark mode. No accounts, no nonsense.”
Frequently Asked Questions
Everything you need to know about ToolMono.
What is ToolMono?+
ToolMono is a free, browser-based developer tools platform offering 76+ utilities — including a JSON Formatter, Base64 Encoder/Decoder, JWT Decoder, Regex Tester, and SQL Formatter — that run entirely in your browser with no server calls, no signup, and no data tracking.
Are ToolMono tools free to use?+
Yes. Every tool on ToolMono is free with no account required, no rate limits, and no paywalls. The platform is independently maintained by a four-person engineering team.
Is my data safe when using ToolMono?+
All processing happens 100% in your browser. No data — including API keys, JSON payloads, JWT tokens, or code — is ever sent to ToolMono servers or any third-party service.
What developer tools does ToolMono offer?+
ToolMono provides 76+ tools across 17 categories: JSON formatting and validation, Base64 encoding/decoding, JWT decoding and verification, regex testing, SQL formatting, text diffing, image conversion, hash generation, UUID generation, YAML validation, and many more developer utilities.
Does ToolMono work offline?+
Most ToolMono tools work fully offline after the initial page load, since all processing runs locally in the browser. Tools that require network access (such as the Webhook Tester) need an internet connection.