ToolStack

About the startup

ToolStack is a collection of 58+ free browser-based tools for developers, marketers, writers, and creators. Every tool works instantly — no account required, no paywall, no forced sign-up. Open the page, use the tool. DEVELOPER TOOLS JWT Decoder — paste any JSON Web Token and instantly decode the header, payload, and signature. Everything runs client-side; your token never leaves the browser. JSON Formatter & Validator — format, minify, and validate JSON with syntax highlighting and clear error messages. SQL Formatter — clean up SQL queries with full dialect support: PostgreSQL, MySQL, SQLite, and T-SQL. Regex Tester — live regex matching with highlight, capture group display, and flag toggles. Write and test patterns as you type. Code Diff Checker — paste two code blocks and get a side-by-side diff with line-level highlighting. Base64 Encoder/Decoder — encode text or files to Base64, decode strings back to readable output. Unix Timestamp Converter — convert between Unix timestamps and human-readable dates in any direction. UUID Generator — generate RFC 4122-compliant UUIDs in bulk, instantly. Markdown Editor — write Markdown with a live preview panel. Copy or export the rendered output. UTM Builder — build properly formatted UTM tracking URLs for campaigns without typos or formatting errors. WHOIS Lookup — query domain registration details, expiry dates, and registrar info. SSL Certificate Checker — verify SSL certificate validity, expiry, and issuer for any domain. Website Down Checker — check whether a site is down for everyone or just you. IP Address Lookup — find geolocation, ISP, and network details for any IP address. DESIGN TOOLS CSS Gradient Generator — build linear and radial gradients with a visual editor and copy ready-to-use CSS output. Color Contrast Checker — test color combinations against WCAG 2.1 AA and AAA accessibility standards. Favicon Generator — upload an image and generate a complete favicon set for all devices and platforms. Color Palette Generator — generate harmonious palettes from a base color using complementary, analogous, and triadic relationships. WRITING & CONTENT TOOLS Word Counter — count words, characters, sentences, paragraphs, and reading time in real time. Character Counter — track counts against limits for Twitter/X, LinkedIn, meta descriptions, and ad headlines. Case Converter — convert text between UPPERCASE, lowercase, Title Case, camelCase, snake_case, kebab-case, and more. Paraphrasing Tool — AI-powered rewriting that restructures sentences while preserving meaning. Grammar Checker — catch grammar, spelling, and punctuation errors with AI-assisted suggestions. Text Summarizer — paste long articles or documents and get a concise summary in seconds. GENERATOR TOOLS AI Prompt Generator — generate structured prompts for ChatGPT, Claude, Midjourney, and other AI tools. Cover Letter Generator — generate tailored cover letters from a job title, company name, and background. Four tone modes: professional, confident, creative, and concise. Business Name Generator — generate brandable business name ideas for any niche. Blog Title Generator — generate SEO-friendly blog titles and headline variations. Meta Description Generator — generate click-worthy meta descriptions optimized for search snippets. Email Signature Generator — build professional HTML email signatures with social links and branding. Hashtag Generator — generate relevant hashtags for Instagram, LinkedIn, and X from any topic. YouTube Tag Generator — generate SEO-optimized tags for YouTube videos to improve discoverability. QR Code Generator — generate QR codes for URLs, Wi-Fi credentials, text, and more. Download as PNG. Lorem Ipsum Generator — generate placeholder text by word, sentence, or paragraph count. Password Generator — generate cryptographically secure passwords with custom length and character rules. PDF Generator — convert text and HTML content to downloadable PDFs directly in the browser. FINANCE & CALCULATOR TOOLS Invoice Generator — create and download professional invoices as PDFs with no account needed. Mortgage Calculator — calculate monthly payments, total interest, and amortization schedules. Compound Interest Calculator — model investment growth with custom principal, rate, frequency, and time period. Salary Calculator — convert between hourly, daily, weekly, monthly, and annual salary figures. Percentage Calculator — solve percentage problems: what is X% of Y, percentage change, and reverse percentage. VAT Calculator — add or remove VAT at any rate. Covers UK, EU, and international pricing. Tip Calculator — split bills and calculate tips for any group size. Age Calculator — calculate exact age in years, months, and days from any birthdate. SECURITY TOOLS Password Breach Checker — check whether a password appears in known data breaches via the Have I Been Pwned API. Uses k-anonymity hashing; the full password is never transmitted.