Technical Specification: Free Online URL Encoder and Decoder

1. Overview

A high-performance, single-file browser utility designed to encode and decode URL strings and query parameters. The application prioritizes privacy and speed, performing all transformations client-side.

2. Core Features

• Live Transformation: Text inputs update in real-time as the user types or toggles between encode/decode modes.
• Dual-Mode Processing: Distinct 'Encode' (converts unsafe characters to percent-encoded) and 'Decode' (reverts to human-readable text) functionality.
• One-Click Copy: A prominent 'Copy to Clipboard' feature with a visual success indicator (Toast notification) instead of browser alerts.
• Example Insertion: A helper button that inserts a complex URL string to demonstrate utility capabilities.
• Input Sanitization: Robust handling of special characters, including spaces, brackets, and non-ASCII characters.

3. UI/UX Specification

• Layout:
  • Header: Centered title and concise tool description.
  • Main Interaction Zone: A split-screen or stacked layout (depending on breakpoint) with two large, clear text areas (Input vs. Output).
  • Control Bar: A row of buttons between the text areas for 'Encode', 'Decode', 'Clear', and 'Copy'.
• Design Aesthetic:
  • Color Palette: Pure white background (#FFFFFF) with a light gray (#F9FAFB) header/footer section. Accent colors in a professional indigo or blue (#4F46E5) for primary actions.
  • Typography: System-ui or Inter sans-serif stack for maximum readability.
  • Shadows: Soft, subtle drop shadows (0 1px 3px 0 rgba(0, 0, 0, 0.1)) on card elements to create depth without clutter.
  • Theme: Strict light-mode configuration. No dark mode toggle.

4. Technical Architecture & Constraints

• Single File: The app must contain all HTML, CSS, and JS in one single file. Do not use external CSS or JS build tools.
• Dependencies: Tailwind CSS via CDN is permitted for layout responsiveness. No complex frameworks like React or Vue.
• Constraint Compliance:
  • No Storage: localStorage, sessionStorage, IndexedDB, and cookies are strictly forbidden. State must be handled entirely in memory.
  • No Blocking Calls: Do not use alert(), confirm(), or prompt(). All user feedback must be via custom, DOM-injected components (e.g., small CSS-animated toast banners).
  • Security: Ensure rel="noopener noreferrer" on all anchor tags. Run code strictly in the context of the provided iframe window.
• Responsiveness: Use CSS Grid/Flexbox to ensure the input/output areas stack vertically on mobile devices and align horizontally on desktop screens.

5. Implementation Guide for Developer

1. Use encodeURIComponent() and decodeURIComponent() for the primary logic.
2. Ensure the UI includes a 'Clear' button to quickly reset both text areas.
3. Add a micro-interaction animation when the 'Copy' button is clicked (e.g., button color flash or checkmark icon transition).
4. Include a small 'Info' section below the main tool explaining what encoding is, which will boost SEO ranking.