Free Online Tools for Everything You Do
Browse 2,706+ free interactive tools - home improvement estimators, pet calculators, cooking converters, automotive tools, finance planners, fitness calculators, developer utilities and more. No sign-up. 100% private. Runs entirely in your browser.
Regex Extractor - Extract Text with Regex Online
Free online regex extractor: extract emails, URLs, phone numbers and dates from text with regular expressions. Dedupe, count, and export matches to CSV, JSON or plain lines. 100% client-side.
IP Address Extractor — IPv4 & IPv6 from Any Text
Free IP extractor: pull valid IPv4 and IPv6 addresses from any text with robust regex, labelled private/public/loopback. 100% client-side.
Regex Split
Split strings using regular expressions.
Regex Strip Special Characters & Pattern Tester
Free online regex tool, pattern matching tester, and generator. Strip special characters, test JavaScript and Python regex replace, and build URL regular expressions.
Regex Tester - Test & Debug Regular Expressions Online
Free online regex tester: test JavaScript regular expressions with live highlighting, flag toggles, capture-group breakdown, find & replace, and a plain-English pattern explainer. 100% client-side.
Regex URL Extractor & Hyperlink Scraper Tool
Standalone url regex, url scraper, hyperlink extractor, web text extractor, and extract url from text. Extract links from webpage, href extractor, regular expression to match url, and link scraper with zero AI slop.
Relative Humidity Calculator — RH from Temperature & Dew Point
Free relative humidity calculator: compute RH from air temperature and dew point (Magnus formula), from absolute humidity, invert to find the dew poin
Relativistic Kinetic Energy Calculator — KE = (γ−1)mc²
Free relativistic kinetic energy calculator: KE from speed, speed from KE, full readout (γ, β, momentum, rest & total energy) and classical vs relativ
REM to PX & Pixel to REM Converter
Standalone professional REM to pixel converter, px to rem calculator, and CSS rem to pixels calculator. Convert rem to px, explore pixel to rem conversion scales, and calculate typography tokens with zero AI slop.
Consonant & Character Remover
High-performance text filtering utility to remove consonants, strip vowels, and clean characters from text.
Remove Duplicates | NRTechStudio
Free online tool to remove duplicate lines from text. Paste lines, deduplicate with case-sensitive or insensitive matching, trim whitespace, keep first or last occurrence, sort A-Z, see removed duplicates with counts, then copy or download.
Rennet Dosage Calculator — How Much Rennet Per Gallon of Milk (Free)
Free rennet dosage calculator: how much rennet per gallon or litre of milk for any cheese. Cross-type converter for liquid single/double strength, tablets and powder, with cheese-style and goat/sheep milk adjustments. 100% client-side, no signup.
Rent Split Calculator — Split Rent Fairly by Sq Ft, Points or Income
Free rent split calculator: split rent with roommates equally, by square footage, by room points, or based on income — with couples adjustment, utilities and surcharges. 100% client-side.
Rent vs Buy Calculator — Break-Even Year, 5% Rule & Full-Cost Comparison (Free)
Free rent vs buy calculator with full-cost modeling: mortgage, PMI, property tax, insurance, HOA, maintenance, selling & closing costs, opportunity cost, break-even year, sensitivity analysis and the 5% rule. 100% private — runs entirely in your browser.
Rental Property Depreciation Calculator - MACRS 27.5 & 39 Year
Free rental property depreciation calculator: MACRS 27.5-year residential and 39-year commercial schedules with the mid-month convention, depreciation recapture estimator and cost segregation guide. 100% client-side.
Requirements.txt Generator — Build pip requirements.txt Online (Free)
Free online requirements.txt generator: pick Python packages, set version pins, add extras, markers and pip options.
Resistor Calculator — Color Code Decoder, Ohm's Law, LED & SMD
Free resistor calculator: 4/5/6-band color code decoder (both directions), Ohm's law solver (V=IR, P=VI), LED series resistor helper, E12/E24 nearest values, and SMD code reader. 100% client-side, no signup.
Resistor Noise Calculator — Johnson–Nyquist Thermal Noise (nV/√Hz, dBu, SNR)
Free resistor thermal noise calculator: Johnson–Nyquist Vn = √(4kTRΔf), noise density in nV/√Hz, noise current, dBV/dBu, available power kTB, and SNR vs your signal level — with cryo & audio presets.
Resistor Voltage Drop Calculator (12V Wire + AWG Table) — nrtechstudio
Compute resistor voltage drop Vd = I x R, % drop vs supply, power dissipated, reverse Imax solver, and 12V/24V automotive wire drop with an AWG copper resistance table. Free, no sign-up.
Resolution Calculator & Scaling Percentage Tool
Interactive resolution calculator, image enlargement calculator, aspect ratio lock, and scaling percentage tool for web and print.
Response JSON Generator
Interactive mock API JSON response generator supporting JSend, JSON:API, RFC 7807, and standard REST HTTP status payloads.
RESTful API – Guide, Builder & Tester
RESTful API guide, define REST API, creating a REST API, REST API service, API creation, API implementation, REST API operations, building RESTful APIs, REST API structure, REST API design example.
Resultant Velocity Calculator - Add Velocity Vectors | nrtechstudio
Free resultant velocity calculator: add up to 10 velocity vectors (components or magnitude plus angle), relative velocity vA/B = vA - vB, and projecti
Resuspension Calculator — Cells, OD600, Beads & Serial Dilution
Free resuspension calculator for cell culture & lab work: pellet cell count to cells/mL, OD600 to cell density, hemocytometer counts, bead/particle concentration, target-volume solver & serial dilution planner.
Retaining Wall Size Calculator — Blocks, Base, Drainage & Cost
Size a retaining wall: block and cap counts, base trench depth, gravel in tons, drainage pipe, geogrid layers for walls over 4 ft, and material cost.
Retirement Savings Calculator — 401(k), IRA, Roth vs Traditional & Social Security | nrtechstudio.com
Free retirement savings calculator with GOAT depth: savings projector, 401(k) employer-match optimizer with 2026 IRS limits, Roth vs Traditional comparator, 4% rule readiness check, Social Security bridge & catch-up planner. 100% private, runs in your browser.
Retirement Withdrawal Calculator - 4% Rule, Guardrails & Bucket Strategy
Model retirement withdrawal strategies: Bengen 4% rule, Guyton-Klinger guardrails,
Reverse Font Generator – Morse Code Translator, Backwards Text & More
Reverse font generator, backwards word generator, upside down text, sideways text generator, morse code translator online, morse code audio generator, morse code solver, and more.
Reverse Text Generator & Upside Down Flip
Free high-performance reverse text generator, backwards text maker, and upside down text converter.
Review & AggregateRating Schema Markup Generator
Interactive Schema.org Review and AggregateRating JSON-LD generator with live Google SERP golden star preview.
Reynolds Number Calculator: Flow Regime, Inverse Solver, Hydraulic Diameter | nrtechstudio.com
Free Reynolds number calculator: Re = rho v D / mu or v D / nu with full unit conversion, pipe and flat-plate flow regime classification, real fluid p
Rgb To Hsv
Convert RGB color values to HSV format.
Rich Text Converter
Interactive Rich Text converter between WYSIWYG HTML, Markdown, BBCode, Plain Text, and Slack markdown.
Right Triangle Volume Calculator
Free online right triangle volume calculator and volume of a triangular prism formula calculator to compute prism volume, hypotenuse, base area, and surface area.
Ring Size Converter — US, UK, EU & Japan Sizes
Free ring size converter: enter finger circumference (mm, cm, inches) or diameter to get US, UK, EU (ISO 8653) and Japanese ring sizes — or convert any standard size back to millimeters. Includes full conversion chart.
Standalone - RIPEMD-160 Generator
Generate RIPEMD-160 cryptographic hashes.
Rise Over Run Calculator: Slope, Percent Grade & Angle
Free rise over run calculator: enter rise and run to get the simplified rise:run ratio, decimal slope, percent grade, angle in degrees, a labeled triangle diagram and full show-your-work steps.
Rise Over Run to Degrees Calculator: Slope Angle, Grade %, Ratio & Roof Pitch
Free rise over run to degrees calculator. Convert rise/run to angle (degrees), grade percent, ratio and roof pitch (x/12) — plus reverse solvers: angle+run to rise, angle+rise to run. 100% client-side.
RLC Circuit Calculator: Series, Parallel, Resonance, Q Factor
Free RLC circuit calculator: series and parallel impedance, phase angle, resonant frequency f0 = 1/(2π√(LC)), Q factor, bandwidth, frequency sweep cha
RMD Calculator - Required Minimum Distribution
Free RMD calculator using the IRS Uniform Lifetime Table (2022+): single-year RMD, full table lookup, multi-year projection. 100%% client-side.
RMS Speed Calculator: Maxwell-Boltzmann v_rms, v_avg, v_mp
Free RMS speed calculator: compute v_rms = sqrt(3RT/M), average speed v_avg = sqrt(8RT/piM) and most probable speed v_mp = sqrt(2RT/M) for 7 real gase
RMS to Watts Converter — Vrms to Watts Calculator (Audio & AC Power)
Convert RMS voltage to watts: P = Vrms²/R for speakers and resistive loads, P = Vrms × Irms × PF for AC circuits, plus reverse solve (find R or Vrms from watts) and audio power presets.
Road Trip Cost Calculator — Gas, EV, Tolls, Hotels, Drive vs Fly (Free)
Free road trip cost calculator: fuel for gas, diesel & EV (Tesla Supercharger), tolls, multi-stop legs, hotels, food, rental car, per-person split, drive-vs-fly comparison, day & fuel-stop planner. 100% client-side, no signup.
Robots.txt Parser & Validator Online
Free online robots.txt checker, robots.txt validator, and robots.txt analyzer. Test robots.txt file, verify robots.txt syntax, generate robots.txt file for SEO.
Rock Tumbling Stage Planner + Grit Calculator (Free) | nrtechstudio
Free rock tumbling lab: 4-stage planner (60/90 to polish), grit calculator by barrel size, Mohs hardness matcher, barrel fill guide, timeline estimator and shiny-rock troubleshooting. 100% private, works offline.
Rockwell Hardness Conversion Calculator (HRC/HRB/HRA to HV/HB)
Convert hardness between Rockwell C, B, A, Vickers (HV) and Brinell (HB) with two-way interpolation from the ASTM E140 empirical tables, an inline chart, and the full reference table.
ROI Calculator & Return on Investment Tool
Free online Return on Investment (ROI) calculator to calculate investment profitability, annualized ROI, net profit margins, and payback periods.
Rolling Offset Calculator — Pipe, EMT Conduit & Bend Marks | nrtechstudio.com
Free rolling offset calculator for plumbers and electricians: 3D pipe rolling offset, travel length, 45-degree shortcut, EMT conduit bend marks, shrink, and fitting takeoffs. 100% in-browser.
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How to Use the Tools Directory
Every tool is a single interactive page: enter your inputs, get instant results, no account needed. Use the search box (shortcut: press /) to jump straight to a tool, or browse categories when you are exploring. Each card links to the tool's permanent URL, which you can bookmark or share.
Because all computation happens in your browser, the tools are fast, private, and free forever. If a result looks wrong, use the one-click report control on the tool page so it can be fixed.
Tool Categories at a Glance
| Category | What you will find | Example tasks |
|---|---|---|
| Developer | Encoders, formatters, regex, network tools | Format JSON, test regex, subnet a network |
| Finance | Tax, loans, salary, investing | Estimate tax brackets, amortize a loan |
| Home improvement | Estimators, measurements, materials | Size a wire, estimate paint or flooring |
| Health & fitness | Body metrics, nutrition, workouts | Track BMI, plan calories, score fitness tests |
| Math & science | Converters, geometry, statistics | Convert units, solve triangles |
| Text | Counters, sorters, generators | Count words, alphabetize a list |
| Color | Pickers, converters, checkers | Convert HEX to RGB, check contrast |
| Everyday life | Cooking, travel, automotive, pets | Convert recipes, plan fuel costs |
Popular Tasks and Where to Start
| I want to... | Start with | Why |
|---|---|---|
| Convert between number bases | Binary Converter | Step-by-step base conversion with charts |
| Validate and format data | JSON Formatter | Pretty-print and check JSON instantly |
| Count words for an essay | Word Counter | Words, characters, reading time |
| Check password strength | Password Strength Meter | Entropy-based strength scoring |
| Grade text readability | Readability Score | Flesch-Kincaid and grade levels |
| Audit color contrast | Accessibility Checker | WCAG contrast ratios in one click |
Tools Directory FAQ
What is the NRTechStudio tools directory?
It is a free catalog of more than 2,700 interactive web tools: calculators, converters, generators, and checkers for developers, finance, home improvement, health, education, and everyday tasks.
Are all the tools really free?
Yes. Every tool in the directory is free to use with no sign-up, no trial, and no paywall. They run entirely in your browser.
Do I need to create an account?
No. There are no accounts, logins, or subscriptions. Open a tool and use it immediately.
Is my data private when I use these tools?
Yes. The tools are 100% client-side: your inputs are processed by JavaScript in your own browser and never sent to a server.
How do I find the right tool?
Use the search box at the top of the directory (press / to focus it), or browse by category. Every tool card shows a short description of what it computes.
Do the tools work on mobile?
Yes. The directory and the tools use responsive layouts that adapt to phones, tablets, and desktops.
How many tools are there?
The directory holds more than 2,700 tools and grows regularly as new calculators and converters are published.
Can I request a new tool?
Yes. Each tool page has a report/feedback control you can use to request features or new tools; requests help prioritize what gets built next.
Are the tools accurate?
Calculators use published formulas and reference data (tax tables, NEC ampacity, standard conversions). Each tool page documents its method, and issues can be reported in one click for a fix.
Do tools work offline?
Once a tool page has loaded, most tools keep working without a connection because the logic is client-side JavaScript. The directory search needs the page loaded first.
What categories are covered?
Developer utilities, finance and tax, home improvement, health and fitness, math and science, text tools, color tools, networking, education, and everyday life calculators, among others.
Can I bookmark or share a tool?
Yes. Every tool has its own permanent URL under nrtechstudio.com/tools/, which you can bookmark or share directly.
Is there an API for these tools?
The tools are interactive web pages, not API endpoints. The underlying math is plain JavaScript you can inspect in the page source.
Why do some tools show ratings?
Ratings aggregate user feedback to surface the most trusted tools and flag pages that need fixes or better explanations.
How often are new tools added?
New tools are published on a continuous pipeline, prioritized by measured search demand and by user requests from the feedback controls.
Who builds these tools?
NRTechStudio, an independent tools studio focused on free, private, client-side utilities that respect user privacy.