Free Developer & SaaS Tools — SaaSQuickStart

A growing library of free online tools for developers and SaaS builders: LLM cost calculators, token counters, regex testers, JWT decoders, and more. 59 tools, all free.

AI / LLM

• LLM API Cost Calculator — GPT-4o vs Claude vs Gemini Pricing — Compare LLM API pricing across GPT-4o, Claude 3.5 Sonnet, Gemini 1.5 Pro, Llama 3, and Mistral. Enter prompt and completion token counts to see cost per request, per 1K, and per 1M requests side by side.
• AI Token Counter — GPT-4, Claude & Gemini Token Calculator — Count tokens in your text for GPT-4, Claude, and Gemini. See token count, word count, character count, and estimated API cost per model. Supports system prompts, conversation history, and long documents.
• AI Prompt Template Builder — Reusable Prompts with {{Variables}} — Build reusable AI prompt templates with {{variable}} placeholders. Fill in variables, preview the final prompt, and copy instantly. Save templates to localStorage. Works with ChatGPT, Claude, Gemini, and any LLM.
• AI Model Comparison 2025 — GPT-4o vs Claude vs Gemini vs Llama — Side-by-side comparison of top AI models: context window, input/output pricing, strengths, and best use cases. GPT-4o, Claude 3.5 Sonnet, Gemini 1.5 Pro, Llama 3, Mistral, and more. Updated 2025.
• AI Coding Agent Slash Commands Cheatsheet — Claude Code, Copilot, Aider, Gemini CLI — Every slash command for the top AI coding agents in one searchable reference: Claude Code, GitHub Copilot Chat, Aider, and Gemini CLI. Plus what Cursor and Windsurf use instead.

Developer

• JWT Decoder — Decode JSON Web Tokens Online — Paste any JWT and instantly decode the header and payload. See all claims, expiry countdown, issued-at time, and signature algorithm. No data sent to any server — runs entirely in your browser.
• Unix Timestamp Converter — Epoch Time to Date Online — Convert Unix epoch timestamps to human-readable dates and back. Live current timestamp, timezone selection, and common reference timestamps (Unix epoch, Y2K, Y2K38). Supports milliseconds and seconds.
• Base64 Encoder & Decoder — Encode & Decode Online — Encode text or files to Base64, or decode Base64 strings back to text. Supports standard Base64 and URL-safe Base64url (no +, /, = padding). Free, instant, private — nothing uploaded.
• JSON Formatter & Validator — Beautify & Minify JSON Online — Format and beautify JSON with proper indentation, validate JSON syntax, or minify JSON for production. Paste your JSON and get instant results with error highlighting.
• UUID & ULID Generator — Generate v4 UUIDs Online — Generate cryptographically secure UUID v4 and ULID identifiers instantly. Bulk generate up to 100 at once, copy all, and choose your preferred format. Uses crypto.getRandomValues().
• Cron Expression Builder — Visual Cron Job Generator & Tester — Build cron expressions visually with hour-range, weekday, and interval options. Supports expressions like */30 9-16 * * 1-5. See plain-English description, next 5 run times, and copy instantly.
• Regex Tester & Explainer — Test Regular Expressions Online — Test regular expressions with live match highlighting, capture groups, and named groups. Get a plain-English explanation of common patterns. Supports JavaScript regex syntax with flags (g, i, m, s).
• URL Encoder & Decoder — Percent-Encode & Decode Online — Encode special characters in URLs (percent-encoding) or decode %xx encoded strings back to readable text. Supports encodeURIComponent and full URI encoding. Handles unicode, spaces, and special characters.
• HTTP Status Codes — When to Use 200, 404, 429, 500 — Complete HTTP status code guide for REST APIs. When to use 200 vs 204, 400 vs 422, 401 vs 403, 404 vs 410, 429 rate limiting, and 5xx errors. Quick decision guide + searchable by code or description.
• MongoDB ObjectID Decoder — Extract Timestamp from ObjectID — Decode any MongoDB ObjectID to extract its embedded creation timestamp, random bytes, and counter. See exactly when a document was created without a separate createdAt field. Also generates new ObjectIDs.
• Webhook Signature Verifier — Debug Stripe, GitHub, Shopify HMAC — Debug webhook HMAC-SHA256 signature failures for Stripe, GitHub, Shopify, or any provider. Paste payload, secret key, and signature header — computed vs received shown side by side. Nothing leaves your browser.
• .env File Parser — Validate & Export dotenv Variables — Paste your .env file to detect duplicate keys, unquoted values with spaces, and invalid key names. Secrets auto-masked. Export as bash source, Docker --env-file, or JSON. Works with dotenv, direnv, and Docker Compose.
• API Rate Limit Calculator — Design Rate Limits by Plan Tier — Design API rate limits per plan tier. Calculate requests/second, burst capacity, daily and monthly quotas. Compare token bucket, fixed window, and sliding window algorithms. Generates 429 response header examples.
• Semver Calculator — Bump Semantic Version Numbers Online — Parse and bump semantic version strings (major, minor, patch, pre-release). Compare two semver strings and understand npm, Go, and Cargo version range implications. Shows next release version instantly.
• cURL Command Builder — Generate curl Commands Online — Build curl commands visually. Select HTTP method, add request headers, body, and authentication (Bearer token, Basic auth, API key header). Live curl output updates as you type. Copy as formatted multi-line command.
• API Key Generator — Design Keys Like Stripe & OpenAI — Generate API keys with custom prefix (sk_live_, pat_, lsk_), length, and character set. Shows entropy in bits. Get Go, TypeScript, and Python generation code. Inspired by Stripe (sk_live_) and OpenAI (sk-) formats.
• JWT Payload Builder — Design JWT Claims Without Signing — Design your JWT payload visually. Toggle standard claims (iss, sub, aud, exp, iat, nbf, jti), add custom claims (role, tenantId), and see the base64url token structure. Includes a Go jwt-go signing code snippet.
• Docker Image Size Estimator — Optimize Before You Build — Estimate Docker image size before running docker build. Choose from 16 real base images (alpine, debian, node, python, golang), add layers for packages and app code, compare single vs multi-stage builds. Get reduction tips.
• OpenAPI Validator — Validate Swagger YAML & JSON Specs — Paste your OpenAPI 3.x or Swagger 2.0 YAML or JSON and instantly catch missing required fields, undocumented operations, missing operationId, and code-gen blockers. No upload required — runs entirely in your browser.
• Text Diff Checker — Compare Two Texts & Find Differences Online — Compare two blocks of text line by line to see exactly what changed. Added lines highlighted green, removed lines red. LCS-based algorithm (same as git diff). Copy unified diff output. Nothing leaves your browser.
• SQL Formatter & Beautifier — Format SQL Queries Online — Paste messy SQL and get cleanly indented, keyword-uppercased SQL instantly. Handles SELECT, INSERT, UPDATE, DELETE, JOINs, GROUP BY, ORDER BY, AND/OR conditions, and CTEs. No data leaves your browser.
• Number Base Converter — Decimal, Hex, Binary, Octal Online — Convert numbers between decimal (base 10), hexadecimal (base 16), binary (base 2), and octal (base 8). Type in any field to update all others. Shows grouped binary and bit length. Supports up to 64-bit values.
• Timezone Converter — World Clock & Time Zone Converter Online — Convert a time from any timezone to multiple world timezones simultaneously. Covers 30+ cities: UTC, New York, London, Tokyo, Sydney, Singapore, Dubai, and more. Handles DST automatically via the IANA timezone database.

SaaS & Business

• Sprint Capacity Calculator — Agile Story Points & Team Velocity — Calculate your team's real sprint capacity in hours and story points, accounting for availability, vacation, and meeting overhead per member. Get a recommended story-point budget for Scrum sprints.
• UTM Link Builder — Google Analytics 4 Campaign URL Generator — Build GA4 UTM campaign tracking URLs instantly. Add utm_source, utm_medium, utm_campaign, utm_term, and utm_content parameters and copy the tracking link. Preview the full URL before sharing.
• MRR & ARR Calculator — Monthly Recurring Revenue for SaaS — Calculate MRR and ARR from multiple subscription plans. Add plans with subscriber counts to get total Monthly Recurring Revenue, Annual Recurring Revenue, ARPU, and a 12-month growth projection.
• SaaS Churn Rate Calculator — Revenue Churn, CLV & Annual Impact — Calculate monthly churn rate, annual churn rate, revenue churn (MRR churn), and customer lifetime value (CLV). See the real dollar impact of losing customers and how reducing churn by 1% affects ARR.
• Startup Runway Calculator — Months of Runway & Burn Rate — Calculate how many months of runway your startup has left. Enter cash balance and monthly burn rate to see runway in months, breakeven point, and what-if scenarios for cutting burn or adding revenue.
• Stripe Fee Calculator — Processing Fees & Net Payout — Calculate exact Stripe processing fees for any charge amount. See net payout for US, international, ACH, SEPA, UK, EU, and AU cards. Includes reverse calculator: what to charge to receive a specific net amount.
• SaaS Metrics Calculator — NRR, LTV/CAC Ratio, Payback Period — Calculate Net Revenue Retention (NRR), LTV/CAC ratio, and CAC payback period. Industry benchmark bands show whether your SaaS metrics are world-class, good, or at-risk. Used by founders and finance teams.
• Stripe Proration Calculator — Upgrade & Downgrade Mid-Cycle Cost — Calculate what Stripe charges when a customer upgrades, downgrades, or changes seat count mid-billing cycle. Shows credit for unused time, charge for new plan, net amount, and the exact Node.js Stripe API call.
• Business Days Calculator — Count Working Days Between Dates — Count business days between any two dates, excluding weekends and public holidays. Supports US Federal holidays, UK Bank Holidays, and custom holiday lists. Perfect for SLA deadlines, sprint planning, and delivery estimates.
• Link Rotator / Traffic Splitter — A/B Test URL Redirect — Split traffic between multiple URLs by weight (60/40, 33/33/33, or any ratio). Generates a self-contained HTML redirect page to host free on GitHub Pages, Netlify, or Cloudflare Pages — no server needed.

Privacy & Security

• EXIF Metadata Remover — Strip GPS & Camera Data from Photos — Remove EXIF metadata from JPEG photos before sharing online. Strips GPS coordinates, camera model, serial number, lens info, and timestamps. 50+ fields cleared. Free, instant, private — runs in your browser.
• Secure Password Generator — Strong Random Passwords Online — Generate cryptographically secure passwords with custom length (8-128 chars), uppercase, lowercase, numbers, and symbols. Bulk generate up to 50 at once. Uses crypto.getRandomValues() — nothing stored or transmitted.
• SHA Hash Generator — SHA-256, SHA-512 Online — Generate SHA-1, SHA-256, SHA-384, and SHA-512 cryptographic hashes of any text or file. Uses the browser's native Web Crypto API — nothing is uploaded to any server.
• JWT Secret Generator — Generate JWT_SECRET & .env Keys — Generate cryptographically secure secrets for JWT_SECRET, JWT_REFRESH_SECRET, AUTH_SECRET (NextAuth), WEBHOOK_ENCRYPTION_KEY, and SESSION_SECRET. Hex, Base64, Base64url output. Equivalent to openssl rand -hex 32.
• TOTP 2FA Generator — QR Code for Google Authenticator & Authy — Generate TOTP secrets and authenticator QR codes to test your 2FA implementation. Scan with Google Authenticator or Authy and watch the live 6-digit code update every 30 seconds. RFC 6238. Nothing leaves your browser.

Content & SEO

• Reading Time Estimator — How Long to Read Any Article — Paste any article, blog post, or document and instantly get reading time at slow, average, and fast speeds. Also shows word count, character count, sentence count, and estimated API cost for LLMs.
• URL Slug Generator — Title to SEO-Friendly URL Converter — Convert any title, heading, or text into a clean, SEO-friendly URL slug. Handles special characters, accents, spaces, and non-ASCII. Supports batch processing of multiple titles at once.
• Meta Tag & Open Graph Preview — Google, Twitter, LinkedIn — Preview how your page looks in Google search results, Twitter/X cards, LinkedIn, and Facebook share previews. Enter title, description, and OG image URL to see live side-by-side previews.
• robots.txt Generator — Block Crawlers & AI Bots Online — Generate a robots.txt file visually. Add allow/disallow rules per user-agent, block AI crawlers (GPTBot, CCBot, Claude-Web), set your sitemap URL, and download the ready-to-use file.
• Google Search Operator Builder — Advanced Search Query Generator — Build advanced Google searches without memorizing syntax. Combine site:, filetype:, intitle:, inurl:, exact phrases, OR, exclusions, and before:/after: date filters, then copy the query or run it on Google.
• Schema Markup Generator — JSON-LD Structured Data for SEO — Generate valid JSON-LD structured data for Organization, Article, Product, FAQ, and Breadcrumb schema. Fill in the fields and copy a ready-to-paste script tag for rich results in Google.
• Sitemap.xml Generator — Free XML Sitemap Builder — Paste your URLs and generate a valid sitemap.xml with lastmod, changefreq, and priority. Copy or download the file to submit to Google Search Console. Runs entirely in your browser.
• Keyword Density Analyzer — Word & Phrase Frequency Checker — Paste any text to see keyword density — single words plus two- and three-word phrases with counts and percentages. Optionally ignore stop words. Spot keyword stuffing and check on-page SEO focus.
• Meta Robots & X-Robots-Tag Generator — noindex / nofollow Builder — Generate the robots meta tag and X-Robots-Tag HTTP header. Toggle noindex, nofollow, noarchive, nosnippet, max-snippet, and max-image-preview, then copy the tag or header.
• Hreflang Tag Generator — Multilingual & International SEO — Generate valid hreflang link tags for multilingual and multi-region pages, including x-default. Paste your language/region codes and URLs to get copy-ready tags.
• WCAG Color Contrast Checker — AA & AAA Accessibility Test — Check if your foreground and background colors meet WCAG 2.1 accessibility standards. Shows contrast ratio, AA compliance (4.5:1 normal, 3:1 large text), and AAA compliance (7:1). Includes color picker.
• Markdown to HTML Converter — Free Online MD to HTML — Convert Markdown to clean HTML instantly. Supports headings, bold, italic, lists, fenced code blocks, blockquotes, and links. Live preview + raw HTML output. Copy and paste into any CMS or rich-text field.

Data & Analytics

• HTML Table to JSON / CSV — Scrape Tables from Any Webpage — Paste HTML from any webpage and extract tables as clean JSON or CSV. Works with Wikipedia, sports stats, financial data, and any HTML source. Handles multiple tables and nested headers. No upload needed.
• CSV Column Remover — Remove & Delete Columns from CSV — Upload any CSV file, select which columns to remove, preview the result, and download a clean file. Works with Excel exports, database dumps, and any comma-separated file. No data leaves your browser.
• A/B Test Calculator — Statistical Significance & P-Value — Determine if your A/B test results are statistically significant. Enter visitors and conversions for control and treatment to get p-value, confidence level, relative lift, and a clear pass/fail verdict.
• Percentage Calculator — % Change, Of, Increase & Decrease — Calculate percentage change between two numbers, find what percentage one number is of another, increase or decrease a value by a percentage. Multiple calculation modes with step-by-step explanations.