Online Tools & Utilities
Free, fast, and easy-to-use web tools for everyone. Streamline your workflow with our comprehensive suite of 266+ utilities.
Try these first — permeability, salinity, molarity, JWT, text-to-speech and more
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From simple text tools to advanced scientific converters, we've got everything you need
Building a Production CLI Tool with Node.js
Ship a production-ready CLI in days, not weeks.
Master the art of building professional command-line tools. From scaffolding to publishing—learn best practices, testing, and deployment strategies used in production.
- Production-ready patterns
- Testing, CI, and npm publish
- Real-world examples
Find the Perfect Tool
Search through our collection of tools or browse by category to find exactly what you need
From the makers
Our products
SaaS tools and books we build alongside Rapid Tools Online — same quality bar, built for real workflows.
SuperApps
Build custom internal apps with tables, calendar, gallery, and more—no code required. Streamline ops and data in one place.
Explore SuperAppsWateronix
Water delivery management for large RO plants in Pakistan: routes, billing, drivers, and reporting—built for serious operations, not chat threads.
See WateronixProduction CLI with Node.js (PDF)
Also in our catalog: ship a production-ready command-line tool—from scaffolding to tests and publish. Same guide promoted site-wide; grab it here too.
View on GumroadAI Apps with Node.js (PDF)
The production AI book for Node.js developers—RAG, agents, streaming chat, and multi-tenant SaaS patterns with TypeScript you can ship.
View on GumroadPopular Tools
Most used converters and utilities — free, instant, no sign-up
AI Tools
Token counter, ChatGPT custom instructions, text chunker, and prompt builders — free and browser-only
AI Token Counter
Count words and characters and estimate ChatGPT, Claude, and Gemini tokens. Context window gauge for 4K–200K. Runs in the browser.
ChatGPT Custom Instructions Builder
Build ChatGPT custom instructions with presets for students, professionals, and creators. Copy each field or download. Runs in the browser.
AI Text Chunker
Split long documents into chunks for ChatGPT and other AI chats. By characters, tokens, or paragraphs with overlap. Copy or ZIP download.
Prompt Generator
Build structured LLM prompts with role, task, context, format, and constraints. Presets for explain, summarize, draft, and more. Copy-ready, runs in the browser.
✨ New Tools
12 new toolsScientific Notation Calculator
Convert numbers to and from scientific notation with arithmetic operations
Carnot Efficiency Calculator
Ideal heat-engine efficiency η = 1 − Tc/Th and related thermodynamics estimates for Carnot cycles
Rotational Dynamics Calculator
Angular momentum L = Iω, torque and angular acceleration for rigid bodies, rolling without slipping helpers
Root Calculator
Calculate nth roots including square root, cube root, and higher order roots
Complex Numbers Calculator
Perform arithmetic operations on complex numbers including addition, subtraction, multiplication, and division
Special Relativity Calculator
Lorentz factor γ, time dilation, length contraction, and relativistic momentum or energy at high speeds
Doppler Effect Calculator
Observed frequency for moving source or observer (sound); optional EM-style recession formulas where applicable
Right Triangle Calculator
Calculate sides, angles, area, and perimeter of right triangles
Snell's Law Calculator
Refraction angles from indices of refraction; critical angle for total internal reflection at an interface
Pythagorean Theorem Calculator
Calculate the length of sides in right triangles using the Pythagorean theorem
Thin Lens Equation Calculator
Object and image distances, focal length, and linear magnification for thin lenses and mirrors (sign conventions)
Remainder Calculator
Calculate the remainder when dividing two numbers (modulo operation)
Recently Updated
12 updatedHash Generator
Generate MD5, SHA1, SHA256, and SHA512 from text or file upload. File hash, checksum from file, verify file integrity. Client-side only.
Calendar
Manage and view events by day, week, or month in a smart calendar interface
Budget Planner
Take control of your finances with comprehensive budget planning. Track income, expenses, set budgets, and achieve financial goals with detailed analytics
Invoice Generator
Create professional invoices with client details, line items, taxes, discounts, and totals. Perfect for freelancers and small businesses
Quote & Estimate Builder
Build clear quotes and estimates with itemized services, optional add-ons, and built-in totals for faster approvals
Expense Tracker
Track daily business expenses by category, add notes, and export summaries for bookkeeping and tax prep
Appointment Scheduler
Create simple appointment schedules, available time slots, and customer bookings
Percentage Calculator
Calculate percentages, percentage increase/decrease, find percentage of a number, and solve percentage problems with step-by-step solutions
Average Calculator
Calculate mean, median, mode, range, standard deviation, and variance with step-by-step calculations and data visualization
Percent Error Calculator
Calculate percent error between experimental and theoretical values
Weighted Average Calculator
Calculate weighted averages where different values have different importance or weights
UUID Generator
Generate RFC 4122 compliant UUIDs (v1 and v4) with multiple output formats for databases, APIs, and applications
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