Free Developer Tools and Converters

Featured Developer Tools tools

JSON ↔ CSV ConverterConverts both ways and flattens nested objects to a depth you set.
Regex Tester & ExplainerHighlights matches and explains every token in plain English.
Cron Expression BuilderTranslates a schedule into plain English and lists the next 5 run times.
Color Contrast CheckerChecks every foreground and background pair against WCAG AA and AAA.

Data & File Converters

6 tools

Move data and documents between formats and pull out the pages or columns you need.

Developers / Data Teams
JSON ↔ CSV Converter
Handles nested objects with configurable flattening depth, null values, and delimiter options. Live preview table.
Nested JSON · auto-detect · preview table
Analysts / Students
CSV Quick Chart Generator
Drop a CSV, pick columns, see a chart instantly. Bar, line, scatter, pie, area, histogram - trendlines, multi-series, outlier detection, color grouping. Download PNG. Zero data leaves your browser.
7 chart types + PNG export
Mapping & GIS
KML to GeoJSON Converter
Convert Google Maps saved places, Google Earth KML/KMZ exports with live map preview and copy to clipboard.
Live map preview
Geospatial
GPX to CSV Extractor
Convert GPS tracks and waypoints into analysis-ready spreadsheets. Preserves elevation, timestamps, and heart rate.
Elevation & HR support
Developers / Students
Markdown to PDF Converter
Paste or upload .md files, pick a theme, and print to clean PDF. Syntax highlighting, tables, task lists, no watermark, no upload, no account.
3 typographic themes
Office Workers
PDF Page Range Splitter
Extract specific pages or page ranges from any PDF entirely in your browser. Thumbnail grid, drag-to-select, multiple named output files, download as ZIP. No upload, no watermark.
Drag-select + ZIP download

Time, Text & Security

7 tools

Timestamps, schedules, patterns, passwords and codes.

Developers
Unix Timestamp Converter
Auto-detects seconds, milliseconds, or microseconds. Bidirectional: type a timestamp or a date. ISO 8601, RFC 2822, relative time, batch convert.
Auto-detect + batch convert
Developers / DevOps
Cron Expression Builder
Type a cron schedule or use the visual builder to get plain English translation and next 5 run times.
Plain English + next 5 runs
Developers
Regex Tester & Explainer
Type a pattern and test string to get highlighted matches, capture groups, and an explanation tree.
Matches + explanation tree
Remote Workers / Teams
Time Zone Meeting Planner
Add up to 6 cities, see a 24-hour working hours grid, find the best overlap time, and copy all times at once.
24h grid + best overlap finder
Developers / Security-Conscious Users
Password Entropy Calculator
Type any password to see entropy in bits, crack times for bcrypt/MD5/online attacks, and weakness explanations. Never transmitted.
Entropy bits + crack time + weakness cards
Developers / CLI Tooling
ASCII Art Text Generator
Type text and pick a font to get FIGlet-style ASCII banner art. Copy as raw, code comment, or hash comment. Standard and Block fonts.
FIGlet-style + copy as comment
Marketers / Developers
QR Code Generator
Create QR codes for URLs, WiFi, vCard, email, and text. Custom colors, PNG download. No watermark, no signup, nothing uploaded.
URL · WiFi · vCard · custom colors

Color, Type & CSS

7 tools

Accessibility checks, shadows, fonts and color matching for print and screen.

Designers / Developers
Color Contrast Checker
Add your palette and check every foreground/background pair for AA and AAA accessibility compliance. Suggested fixes, Tailwind paste, CSV export.
WCAG AA · AAA · full matrix
Frontend Developers / Designers
CSS Box Shadow Generator
Layer multiple shadows visually, adjust offset, blur, spread, and color per layer, then copy the CSS. Includes Material, neumorphism, and soft UI presets.
Multi-layer + presets + copy CSS
Designers / No CSS knowledge
Font Pairing Preview Tool
Pick a heading and body font, type your own text, and see a live preview. Copy the CSS import snippet.
Live preview + CSS snippet
Designers / Frontend Developers
Typographic Scale Generator
Pick a ratio and base size to get a harmonious font scale as CSS variables with optional fluid clamp() values. Tailwind config export included.
CSS vars + fluid clamp() + Tailwind
Designers
Image Color Palette
Drop any photo to get dominant colors as hex codes using k-means clustering - entirely in your browser. Copy as CSS variables, SCSS, or Tailwind config.
CSS + SCSS + Tailwind export
Print Designers
CMYK to Pantone Approximator
Find the nearest Pantone Solid Coated color from CMYK, HEX, RGB, or LAB input using Delta-E color distance. Top 3 matches, copy PMS code.
Delta-E · top 3 Pantone matches
Industrial Designers / Contractors
Pantone to RAL Converter
Find the nearest RAL Classic match for any Pantone Solid Coated code using Delta-E color distance. Top 3 matches with quality rating.
Pantone <-> RAL + Delta-E matching

Images & Storage

2 tools

Resize photos in bulk and plan disk arrays.

Designers / Marketers / Developers
Batch Image Resizer & Converter
Drop up to 50 photos, set a resize rule, choose JPEG/PNG/WebP output, and download all as a ZIP. No uploads, no account, nothing leaves your browser.
50 images · WebP · ZIP download
IT / Sysadmins / NAS Users
RAID Storage Calculator
Configure drives and RAID level to get usable space, fault tolerance, and rebuild time estimate. Compare all RAID levels side by side.
Usable space + fault tolerance + RAID comparison

AI Costs & Context

3 tools

Estimate what AI assistants and agents cost and how much of a context window a text uses.

Individual Developers
AI Coding Assistant ROI Calculator
See if your Copilot, Claude, or other AI coding subscription pays for itself based on the hours it actually saves you.
Net value + breakeven hours
AI Agent Builders
AI Agent Task Cost Calculator
Token calculators price a single prompt - this estimates the real cost of an autonomous agent chaining many tool calls per task.
Per-task cost + multi-step multiplier
Developers / Prompt Engineers
Context Window Budget Planner
Paste text or enter a word count to see estimated tokens used, percent of the model's context window consumed, and how many copies would fit.
Tokens used + % of context window + copies that fit

Which tool do I need?

Flatten JSON into a spreadsheet, or the reverseJSON ↔ CSV Converter
Chart a CSV without opening a spreadsheetCSV Quick Chart Generator
Convert a Unix timestamp to a dateUnix Timestamp Converter
Write or decode a cron scheduleCron Expression Builder
Test a regular expressionRegex Tester & Explainer
Check that text and background colors are accessibleColor Contrast Checker
Build a type scale as CSS variablesTypographic Scale Generator
Pull a color palette out of a photoImage Color Palette
Pull a few pages out of a PDFPDF Page Range Splitter
Resize a folder of photosBatch Image Resizer & Converter
Find a meeting time across time zonesTime Zone Meeting Planner
See how much of a context window a text fillsContext Window Budget Planner

Developer Tools FAQ

Are files uploaded when I use these tools?

No. Conversion, resizing and PDF splitting all run in your browser, so your files stay on your device.

How do I convert nested JSON to CSV?

Paste the JSON into the JSON to CSV converter. It flattens nested objects to a depth you configure, handles null values and lets you choose the delimiter, with a live preview table.

How do I read a cron expression?

Type it into the cron expression builder. It translates the schedule into plain English and lists the next 5 run times.

What does the color contrast checker test?

It checks each foreground and background pair against WCAG AA and AAA and suggests fixes for pairs that fail.

How does the password entropy calculator estimate crack time?

It computes entropy in bits for the password you type and shows crack times for bcrypt, MD5 and online attacks. The password is never transmitted.

Can I export the results as code?

Several tools copy straight into a project. The palette extractor copies CSS variables, SCSS or a Tailwind config, and the type scale generator exports CSS variables with optional clamp() values.

Free Developer Tools