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.
Java Escape — Escape & Unescape Java Strings Online
Free online Java string escape tool. Escape quotes, backslashes, newlines, tabs and Unicode into valid Java string literals (JLS §3.10.6), or unescape Java literals back to text. 100% client-side.
Java to JSON Converter
Convert Java Class and POJO model definitions into valid mock JSON objects instantly with Jackson, Gson, and Lombok support.
JavaScript Beautify – JS, YAML & Markdown Formatter
Yaml formatter, javascript beautify, yaml 格式化, formatter js, javascript style, markdown generator, markdown examples, url formatter, notepad json formatter, markdown link image, pretty format json, markdown text editor, yaml file formatter, markdown indent image, markdown javascript, online formatter js, js 格式 化, online formatter javascript, markdown file type, what is markdown editor, javascript prettify online, javascript beauty, markdown website, markdown show image, javascript markdown renderer, markdown rendered, yaml creator, markdown inline images, js 格式化, online yaml viewer.
JavaScript Code Editor, Web Sandbox & Next.js vs React Guide
Free in-browser JavaScript code editor and web playground. Run JavaScript scripts, test HTML/CSS/JS, execute console outputs, inspect Next.js vs React architectures, and access modern boilerplates.
JavaScript JSON Serializer & Parser
Interactive JavaScript JSON.parse vs JSON.stringify testing playground, safe deserializer, and Node.js code generator.
JavaScript Map to JSON Serializer
Interactive converter and code generator for serializing ES6 Maps, Sets, and BigInt to JSON and back.
JavaScript Next & Next.js Online Editor
Free online JS code editor, JavaScript Next playground, and Next.js releases tracker. Test ES2024 features and inspect Next.js logo assets.
JavaScript Pretty Print JSON & Beautifier
Interactive JSON validator, JavaScript JSON formatter, Java POJO generator, and HTML code beautifier tool.
JavaScript Replace Replace – String Replace & Split Tool
Javascript replace replace, javascript split string, remove char from string, javascript remove from string, javascript substring split, javascript remove string from string, trim whitespace js, javascript remove whitespace from string, js remove from string, javascript strip whitespace, string replace online, remove spaces online, remove spacing word, how to get rid of spaces in word, word remove extra spaces, eliminate spaces, js split string by character, javascript string in string, new line to comma online, javascript remove spaces, remove spacing.
Job Offer Comparison Calculator — Total Compensation Compared | nrtechstudio.com
Free job offer comparison calculator: compare up to 3 job offers side by side on total compensation — base salary, bonus, RSU equity vesting, 401(k) match, PTO value, health premiums, taxes, and remote vs onsite costs. 100% client-side, no signup.
Job Posting Schema Generator
Interactive Google for Jobs compliant Schema.org JobPosting structured data generator with remote work and salary support.
JQ Format JSON & Query Playground
Interactive online JQ query evaluator, JSON formatter, and filter expression tester.
JavaScript JSONPath Evaluator
Interactive JSONPath query evaluator, expression tester, and JavaScript code generator.
JS Linter — Check JavaScript Code Online
Free online JavaScript linter. Heuristic client-side JS code checker: var vs let/const, == vs ===, missing semicolons, console.log leftovers, debugger, eval, unbalanced braces. No uploads.
JS Minifier — Minify JavaScript Online Free
Free online JS minifier — minify JavaScript code, compress JS, strip comments and whitespace, reduce file size. Includes JS beautifier, syntax validator and console.log detector. 100% client-side.
JS Object to CSS Converter - React Inline Styles to CSS
Convert JS style objects to CSS: React inline styles or Emotion/JSS objects become kebab-case CSS with automatic px units, &:hover and @media support.
JavaScript Formatter & Beautifier Online
Free online JavaScript formatter and JS code beautifier. Format JS code, javascript formatting online, JS code formatter, javascript code formatter, javascript beautification, javascript code beautifier, javascript formatting, js code beautify, format js code online.
JavaScript & JSON Unescape Tool & String Decoder
Standalone professional JavaScript unescape tool, JSON unescape utility, and JS string decoder. Escape characters JS, javascript escape string, and unescape JS strings online with zero AI slop.
JSON Encode
Online JSON encoder and PHP json_encode() simulator with customizable bitmask flags (unescaped slashes, unicode, pretty print).
JSON Escape Unescape — Online JSON String Tool
Free online JSON escape/unescape tool: escape any string for embedding in JSON (minimal or full \uXXXX unicode mode) or unescape JSON strings back to raw text. 100% client-side.
JSON Feed Generator — Create JSON Feed 1.1
Free JSON Feed generator — create valid JSON Feed 1.1 online with live preview, validation, and one-click download.
Json Formatter
Format, validate, and minify JSON data.
Json Generator
JSON Key Case Converter
Recursively convert JSON property naming conventions between camelCase, snake_case, PascalCase, and kebab-case online.
JSON Key Extractor - List All Keys & Paths from JSON Online
Free JSON key extractor: list every key from nested JSON as unique names or full key paths (dot, bracket, JSONPath, Python), with counts, depth limit, and prefix filter.
JSON Linter & Validator
Professional JSON Linter, Object Validator, Syntax Error Checker, and Online JSON Corrector.
JSON Minifier & Compressor
Standalone professional JSON minifier, compressor developer utility, and payload size reducer. Compress JSON data tool with syntax validation, gzip estimation, and file export.
JSON to Swift Codable Struct Generator
Interactive converter that transforms JSON payloads into idiomatic Swift Codable structs with CodingKeys.
JSON Parser, Validator & String Unescape Tool
Free online JSON parse and validator tool. Escape JSON online, unescape JSON online, unescape JSON string, and C string unescape online.
Json Path Finder
JSON Prompt Generator
Interactive prompt engineering tool to generate schema-constrained JSON system prompts and structured output payloads for LLMs.
JSON REST API Mock Server
Interactive mock REST API endpoint designer, response simulator, and client code snippet generator.
JSON Schema Validator — Free Online JSON Schema Tester, Checker Playground
Free online JSON Schema validator: paste a JSON document and a schema to test validity instantly. Precise error paths (JSON Pointer), drafts 2020-12 / 2019-09 / 7, $ref, formats, YAML schemas. 100% client-side — offline & private.
JSON Schema Viewer
Interactive visual JSON Schema tree explorer, documentation viewer, and sample mock data generator online.
Json Stringify
JSON to Array JS Converter
Convert JSON objects and keys into JavaScript arrays using Object.entries, Object.values, and array transformations online.
JSON to C# Class Converter
Free online JSON to C# class converter — paste JSON and generate C# POCO models with Newtonsoft or System.Text.Json attributes, nullable types, nested classes and List<T> arrays. 100% client-side.
JSON to Documentation & Word Converter
Interactive tool that converts JSON data into formatted technical documentation, Microsoft Word documents, and Markdown tables.
Json To Html
Json To Json Schema
JSON to JSON Transformation Tool
Interactive declarative JSON mapper and schema transformer for reshaping, flattening, and restructuring JSON payloads.
JSON to JSONL Converter
Convert JSON arrays into JSON Lines (JSONL / NDJSON) and vice versa for OpenAI fine-tuning and BigQuery ingestion.
JSON to PHP Array Converter
Convert JSON strings and objects into formatted PHP associative arrays with short bracket [] or array() syntax.
JSON to Python Class Converter
Free online JSON to Python class converter — turn JSON into dataclasses, Pydantic v2 models, attrs classes or TypedDicts with live type inference. 100% client-side.
JSON to Rust Struct Converter
Free online JSON to Rust struct converter - generate serde Serialize/Deserialize structs with Option, Vec, HashMap, nested types and rename attributes. 100% client-side.
JSON to Text Converter
Convert complex JSON documents into clean, human-readable plain text, bulleted outlines, and key-value summaries.
JSON to TOML Converter
Free online JSON to TOML converter — paste JSON or upload a .json file, get clean TOML config with tables, array tables, honest null handling, and ISO-8601 datetime detection. 100% client-side.
Json To Typescript
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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.