Free Developer & Code Tools & Calculators
Browse 326+ free interactive developer & code calculators, estimators, and utilities. 100% free, private, and runs directly in your browser without signup.
Country Calling Code Lookup — Reverse Phone Code Lookup for 230+ Countries
Free country calling code lookup: paste any phone number to identify its country (+62, +44, +1…), search 230+ country dial codes, check driving side, capitals and currencies. 100% private, runs in your browser.
Cron Expression Explainer — Describe, Validate Test Cron Jobs (Free)
Free cron expression explainer, generator, validator and tester. Paste any cron expression to get a plain-English description, next run times with timezone & DST checks. Supports standard 5-field, Quartz 7-field and AWS EventBridge cron. 100% client-side — nothing leaves your browser.
Cron to Quartz — Convert Linux Cron to Java Quartz Cron
Convert Linux crontab expressions to Java Quartz cron format online. Paste a 5-field cron, get a valid 7-field Quartz expression with field-by-field mapping, validation and warnings. Free, 100% client-side.
Crontab Generator — Build Cron Schedules Visually (Free)
Build crontab lines visually: free crontab generator with presets and per-field controls, plain-English description and next 5 run times. 100% client-side.
Csharp To Vb Net
CSS Entity Encoder
Free online CSS entity encoder — convert any text into CSS hex escapes (\48\65\6C\6C\6F). Full & safe-only modes, decode-back verification, live examples. 100% client-side, no signup.
CSS Escape
Free online CSS escape tool — escape special characters for CSS selectors, identifiers, and strings. Spec-accurate CSS.escape() identifier escaping plus content-string mode. 100% client-side, no signup.
CSS Filter Generator & Visual Filters Builder
Standalone professional CSS filter generator, visual CSS filters builder, and CSS image filters generator. Generate CSS image filters, customize img filter CSS, and build photo effects with zero AI slop.
CSS Linter Online
Free online CSS linter — check CSS syntax errors, warnings and best practices with line numbers. 100% client-side.
CSS Minifier & Beautifier
Free online CSS minifier and beautifier — minify CSS code, compress stylesheets, strip comments and whitespace, reduce file size, or format CSS online. 100% client-side, no signup.
CSS to JS Object Converter
Free CSS to JS object converter: CSS rules to React inline-style objects, React Native StyleSheet and TypeScript CSSProperties. 100% client-side.
CSS Unescape
Free online CSS unescape tool — decode CSS escape sequences (hex escapes like \31 and char escapes like \:) back to normal characters. Spec-accurate per CSS Syntax Level 3, with escape highlighter, batch mode, live proof, copy & download. 100% client-side, no signup.
CSV Column Extractor — Free Online CSV Column Extractor
Free CSV column extractor: pull columns by index or name. Auto-detects delimiters, handles quoted fields, exports CSV, JSON, or list. Private, in-browser.
CSV Analyzer Online — Free CSV Data Profiler (Stats, Types Quality Score)
Free online CSV analyzer: paste or upload a CSV file to profile every column — inferred types, null & unique counts, mean/median/std, outlier detection and a data quality score. 100% client-side, your data never leaves the browser.
CSV Linter — Free Online CSV Validator & Format Checker
Free CSV linter online: find ragged rows, unbalanced quotes, mixed delimiters, BOM, blank rows and line-ending issues. 100% private, runs in your browser.
CSV to JSON Converter - Free Online Bidirectional Tool
Free CSV to JSON converter: RFC 4180 parser, delimiter auto-detect, live preview, download. Bidirectional JSON to CSV included. 100% client-side.
CSV to PHP Array Converter - Free Online Tool
Free CSV to PHP array converter: paste CSV and generate PHP array code (short [], array(), var_export) with delimiter auto-detect, type casting, copy & download. 100% client-side.
CSV to TSV Converter - Free Online One-Way Tool
Free CSV to TSV converter: RFC 4180 parsing, honest tab policy, live table preview, file upload, download. One-way csv to tsv only. 100% client-side.
CSV to XML Converter — Free Online CSV to XML Tool
Convert CSV to XML online free. RFC 4180 CSV parser, delimiter auto-detect, custom root/row elements, per-column attribute mapping, namespaces — 100% client-side.
CSV to YAML Converter
Free online CSV to YAML converter — turn spreadsheets into clean YAML with type inference, dot-notation nesting, custom delimiters, live preview and instant download. 100% client-side.
Cube Density Calculator — Mass, Volume & Density
Free cube density calculator: enter any two of mass, side length, or density to find the third. Density of a cube formula ρ = m / s³, with unit conversions and worked steps.
cURL GET Request Generator
Interactive cURL GET request builder with query parameters, headers, bearer token auth, and code export.
cURL HEAD Request Generator & Inspector
Generate cURL HEAD commands and analyze HTTP response headers, redirect chains, and security headers online.
Curl Online
cURL POST Request Generator
Interactive cURL POST request builder supporting JSON payloads, form-data, multipart uploads, and language code export.
cURL to JavaScript Converter
Convert cURL CLI commands into clean modern JavaScript code for Fetch API, Axios, and Node.js.
Curl To Python
OSHA DART Rate Calculator — Days Away, Restricted or Transferred
Compute workplace-safety DART rate and TRC rate with the OSHA formula: (case count × 200,000) / total hours worked. Includes an industry-average comparator and an explanation of the 200,000 figure.
Date to Roman Numerals Converter — Write Any Date in Roman Numerals (Free)
Free date to Roman numerals converter: turn any calendar date into Roman numerals (VII.X.MMXXVI), with show-your-work steps, Latin month names, decode mode, and copy. 100% client-side — your dates never leave the browser.
Defensive Interval Ratio (DIR) Calculator — Measure Defensive Liquidity
Calculate the defensive interval ratio: (current assets − inventory) ÷ daily operating expenses. Includes a target DIR solver, 2-company comparator, interpretation table, and DIR vs current ratio vs cash ratio FAQ.
Delta to Wye (Δ-Y) Conversion Calculator — 3-Phase Balanced & Unbalanced
Free delta to wye conversion calculator: balanced Δ-Y (Z_Y = Z_Δ/3), unbalanced delta to wye and wye to delta transformations, R/L/C networks with frequency, plus 3-phase line vs phase voltage/current and power. 100% client-side — no data leaves your browser.
Density to Weight Calculator — Convert Density × Volume to Mass | nrtechstudio.com
Free density to weight calculator: enter density and volume to get weight (mass) instantly. W = ρ × V with multi-unit support — kg/m³, g/cm³, lb/ft³, liters, gallons, cubic feet — plus a material density table (steel, water, concrete, gold). 100% in-browser, no sign-up.
Text Comparison & Diff Checker
Professional online text comparison tool to compare two texts for differences, find difference between two texts, and check similarity with highlighted diff output.
DNA Concentration Calculator — A260 to ng/µL, Purity & Yield | nrtechstudio.com
Free DNA concentration calculator: convert A260 absorbance to ng/µL for dsDNA, ssDNA, RNA and oligos, with dilution factor, pathlength correction (NanoDrop), A260/A280 & A260/A230 purity ratios, and total yield. 100% client-side — your data never leaves the browser.
DNS Lookup Tool & DNS Toolbox
High-performance DNS lookup tool, DNS search tool, zone file generator, nameserver finder, and CLI command generator.
Dog Age Calculator: Dog Years to Human Years
Free dog age calculator: convert dog years to human years with 4 size profiles and 3 methods side-by-side — AVMA, AKC chart, Wang 2020. 100% client-si
Dog Run Size Calculator — Outdoor Kennel Run Dimensions, Fence Height & Materials
Free dog run size calculator: plan the perfect outdoor run with dimensions by breed, fence height, material takeoff, gravel & shade. Imperial + metric
Dry Matter Calculator — As-Fed to Dry Matter Basis Converter | nrtechstudio.com
Free dry matter calculator: convert pet food and livestock feed nutrients from as-fed to dry matter basis, compare up to 3 products side by side, reverse-convert for ration formulation, and check hay/silage moisture safety. 100% client-side.
Dummy Data Generator for Developers & SQL Data Generator
Free online dummy data generator for developers and SQL data generator to generate mock database records, SQL INSERT statements, JSON arrays, and CSV datasets.
Dummy Image URL Generator
Free dummy image URL generator — build placeholder image links for placehold.co,
Earned Value Management (EVM) Calculator — CPI, SPI, EAC, TCPI
Free Earned Value Management (EVM) calculator: compute CPI, SPI, CV, SV from PV, EV, AC; estimate EAC & ETC; and TCPI. With an interpretation table, worked examples, and FAQ.
ECDSA Key Generator
High-Security ECDSA Key Pair Generator, Crypto Elliptic Curve Key Creator, and Digital Signature Playground with 100% SEMrush keyword optimization.
Email Extractor & Online Email Scraper Tool
Free online email extractor to extract email addresses from text, web pages, or documents. Bulk email extractor, email scraper, and email address extractor with instant regex-powered results.
Email to MD Link — Free Mailto Markdown Link Generator
Free mailto link generator: turn any email into a Markdown [text](mailto:) link with subject, body, CC/BCC, escaping & obfuscation. 100% client-side.
Enterprise Resource Planning Software Guide & Planner
Interactive enterprise resource planning software architecture planner, module cost estimator, top ERP platforms comparison, and small business readiness assessment.
Enterprise Value (EV) Calculator — EV Formula from Components
Compute enterprise value from its components: market cap + total debt − cash and cash equivalents. Includes a reverse solver, an EV-to-equity-value bridge waterfall, and a two-company comparator.
Er Diagram Generator
ESLint Config Generator
High-performance interactive ESLint Flat Config and .eslintrc.json builder with TypeScript, React, Next.js, and 100% SEMrush keyword optimization.
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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.