Free · No Signup · Browser-Only
Free Online Tools for Developers and Data Scientists
Browser-based utilities that run entirely on your device. Zero tracking, zero data sent to any server, zero signup required.
JSON Formatter & Validator
Format, validate, and minify JSON instantly. Detect syntax errors with line numbers. Copy or download the result.
- Developer
- JSON
- Validator
Word Counter & Text Stats
Real-time word, character, sentence, and paragraph counts. Reading time estimate and top keyword density.
- Writing
- SEO
- Readability
Sleep Cycle Calculator
Calculate the ideal bedtime or wake-up time based on 90-minute sleep cycles. Wake up refreshed, not groggy.
- Health
- Sleep
- Calculator
BMI & Healthy Weight Calculator
Calculate your Body Mass Index, healthy weight range, and category. Supports metric and imperial units.
- Health
- Fitness
- Calculator
Heart Rate Zone Calculator
Calculate your 5 heart rate training zones using the Karvonen formula. Enter age and resting heart rate.
- Health
- Fitness
- Training
Base64 Encoder / Decoder
Encode plain text to Base64 or decode Base64 back to text instantly. Supports files and Unicode.
- Developer
- Encoding
- Utility
Color Contrast Checker (WCAG)
Check if your foreground/background color combination passes WCAG AA and AAA accessibility standards.
- Design
- Accessibility
- WCAG
Password Strength Checker
Analyze password entropy, estimate crack time, and get specific improvement tips. 100% local — never sent to a server.
- Security
- Privacy
- Utility
Readability Analyzer
Paste text and get 6 readability scores: Flesch-Kincaid, Gunning Fog, Coleman-Liau, SMOG, ARI, and more.
- Writing
- SEO
- Content
Markdown Editor & Previewer
Split-pane Markdown editor with live HTML preview. Supports headings, tables, code blocks, and more.
- Developer
- Writing
- Markdown
Meta Tags Preview Tool
Preview how your page looks in Google, Twitter/X, and LinkedIn before publishing. Generates ready-to-copy HTML tags.
- SEO
- Developer
- Social Media
CSV Chart Visualizer
Upload a CSV file and instantly generate a line, bar, or area chart. Pick any two columns as axes — your data never leaves your browser.
- DataViz
- Data Science
- CSV
100% Private by Design
Every tool on this page runs entirely in your browser. Your text, files, and data never leave your device. No API calls, no analytics on tool inputs, no accounts.
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