OnlineFreeTools.org
  • Home
  • Image editing tools
    • Add Text Watermark to Photo — Local Browser Tool
    • Extract Colors from Image — Palette & Click Pick
    • Flip Image — Mirror Horizontally or Vertically
    • Add Border to Image — Color & Width Online
    • Image Compressor — Resize, Quality & Target Size Local
    • Crop & Resize Image — Local Aspect Presets
    • Photo EXIF Viewer & Remover — GPS, Camera & Local Strip
    • Image Format Converter — PNG JPEG WebP AVIF BMP GIF ICO SVG
    • Convert Image to Grayscale — Black & White Online
    • Merge Images — Combine Photos into One Collage
    • Image Optimizer — WebP, AVIF & MozJPEG Local
    • Overlay Images — Put a Logo on a Photo
    • Image to Base64 Converter — Encode & Decode Locally
    • Images to GIF — Make an Animated GIF Locally
    • Images to PDF — Combine Photos into One File
    • Images to PowerPoint — Photos to PPTX Slides
    • Images to Word — Build a DOCX from Photos
    • PDF Page to Image Sizes — Multi-Size Export Pack
    • PDF to JPG — Convert Pages to Images in Your Browser
  • Design tools
    • Generate Brand Color Scale — 50–950 Palette & CSS Tokens
    • Brand Style Guide — Generate a Modular Draft You Can Edit
    • Smart Website Color Scheme — Semantic CSS Tokens
    • WCAG Contrast Checker — AA/AAA Ratio Online
  • PDF tools
    • Compress PDF — Shrink File Size in Your Browser
    • Crop PDF — Trim Page Margins in Your Browser
    • Merge PDF — Combine Files in Your Browser
    • Organize PDF — Reorder or Remove Pages in Your Browser
    • Add Page Numbers to PDF — In Your Browser
    • PDF to Markdown — Extract Text for Notes in Your Browser
    • PDF Watermark — Stamp Text on Every Page in Your Browser
    • Protect PDF — Password-Encrypt in Your Browser
    • Rotate PDF — Fix Page Orientation in Your Browser
    • Split PDF — Extract Pages Locally
    • Unlock PDF — Remove Password You Already Know
  • Developer
    • Add WWW to DNS — A/CNAME, Apex Rules & Provider Guides
    • Archive Extractor Online — Open Compressed Files in Your Browser
    • Base64 Encode & Decode — Convert Text in Your Browser
    • CIDR to IP range — Expand a prefix into usable addresses
    • Core Web Vitals Checker
    • CSV ↔ JSON Converter — Types, Delimiters & Local
    • Domain Lookup — Check DNS Records & Registration Online
    • File Hash Checker — Verify Digests in Your Browser
    • Hreflang Generator
    • HTML Entity Encoder & Decoder — Escape, Unescape & Local
    • IndexNow — Bing URL Submit, Key Check & Status Codes
    • What Is My IP Address — See Your Public IP (IPv4 or IPv6)
    • IP range to CIDR — Turn start–end addresses into prefix lists
    • JSON Schema Validator — Draft-07 Paths & Local
    • JWT Decoder — Read Header & Payload Locally (No Verify)
    • Magnet Link Decoder — Parse Info Hash and Trackers Locally
    • Markdown ↔ HTML
    • Google SERP Preview
    • Meta Tag Generator
    • On-Page SEO Checker
    • Open Graph Preview
    • Random Password Generator — Create Passwords Locally
    • Private CIDR ranges — Check if an IP or prefix is private or special-use
    • Robots.txt Generator
    • JSON-LD Schema Generator
    • XML Sitemap Generator
    • Terraform cidrsubnet — Get the child CIDR Terraform would return
    • Compare Two Texts Online — Text Diff Checker
    • Time Zone Converter — Compare One Moment Worldwide
    • Unix Timestamp Converter — Epoch ↔ Readable Time
    • Unzip File Online — Extract ZIP Files in Your Browser
    • UTM Builder
    • UUID & ULID Generator — Create IDs in Your Browser
    • Check HTTP Response Headers
    • YAML ↔ JSON Converter — Types, Multi-doc & Local
  • Calculators
    • Acceleration Calculator — Change in Velocity
    • Age Calculator — Chronological Age from Birthdate
    • Aspect Ratio Calculator — How to Calculate and Scale Ratios
    • BMI Calculator — How to Calculate Body Mass Index
    • BMR & TDEE Calculator — How to Calculate Daily Calories
    • Body Fat Calculator — How to Estimate Body Fat Percentage
    • Break-Even Calculator — How to Calculate Break-Even Point
    • CAGR Calculator — How to Calculate Compound Annual Growth Rate
    • Circle Calculator — Area and Circumference
    • Compound Interest Calculator — How to Calculate Future Value
    • Concrete Calculator — How to Estimate Concrete Volume
    • Confidence Interval Calculator — How to Calculate a CI
    • Contribution Margin Calculator — Price Minus Variable Cost
    • Date Difference Calculator — Days and Weeks
    • Debt Payoff Calculator — Months to Clear a Balance
    • Density Calculator — Mass over Volume
    • Discount Calculator — How to Calculate Sale Price
    • EMI Calculator — How to Calculate Loan Payments
    • Exponent Calculator — How to Calculate Powers
    • GPA Calculator — How to Calculate Weighted GPA
    • Gradient Calculator — Multivariable ∇f (Partial Derivatives)
    • Gross Margin Calculator — How to Calculate Gross Margin
    • Heart Rate Zone Calculator
    • Ideal Weight Calculator — How to Estimate Ideal Body Weight
    • Inflation Calculator — Future Purchasing Power
    • IRR Calculator — Internal Rate of Return
    • Logarithm Calculator — How to Calculate Logs
    • Macro Calculator — Calories to Protein Carb Fat Grams
    • How to Calculate Marginal Revenue — MR Calculator (ΔTR / ΔQ)
    • Markup Calculator — How to Calculate Markup Percentage
    • Mean Calculator — Average of a Number List
    • Median and Mode Calculator
    • How to Calculate NPV — Net Present Value Calculator
    • Ohm’s Law Calculator — Resistance and Power
    • One-Rep Max Calculator (Epley)
    • P-Value Calculator — How to Calculate a P-Value
    • Pace Calculator — min/km and Speed
    • Paint Calculator — How to Estimate Paint Needed
    • Payback Period Calculator — Years to Recover Investment
    • Percentage Change Calculator — From Old Value to New
    • Permutation and Combination Calculator
    • Present Value Calculator — PV and FV Modes
    • Profit Margin Calculator — Net or Operating Margin
    • Pythagorean Theorem Calculator — How to Find a Missing Side
    • Quadratic Equation Solver — Roots and Discriminant
    • ROI Calculator — How to Calculate Return on Investment
    • Rule of 72 Calculator — Years to Double
    • Salary to Hourly Calculator — How to Convert Pay Rates
    • Sample Size Calculator — How to Estimate Required n
    • Scientific Notation Calculator — How to Convert Scientific Notation
    • Significant Figures Calculator — How to Count and Round Sig Figs
    • Slope Calculator — How to Calculate Slope Between Two Points
    • Standard Deviation Calculator — How to Calculate SD and Variance
    • Tile Calculator — How to Estimate Tile Quantity
    • Tip Calculator — Tip Amount and Split
    • Triangle Area Calculator
    • VAT / GST Calculator — Add or Extract Tax
    • Velocity Calculator — Distance over Time
    • Volume Calculator — Box and Sphere
    • Z-Score Calculator — How to Calculate a Standard Score
    • Measuring Magnetic Fields — Field strength calculator
    • Square Feet to Square Meters — Area Converter for Homes & Renovation
    • Unit Converter — Length / Mass / Temperature / Area / Volume / Speed
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  • Dev Logs

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Dev Logs

Browse Q&A and implementation notes by month. GitHub

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2026-01

  • 更新不记录AI末尾提问规则 2026-01-08
  • 更新README中英文 2026-01-08
  • 删除历史中的文件夹 2026-01-08
  • 初始化Cloudflare项目 2026-01-08
  • 创建开发日志文件夹 2026-01-08
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