Private Developer Tools. No Uploads.
Format, decode, convert and inspect sensitive developer data directly in your browser.
-H 'Content-Type: application/json' \
-H 'Authorization: Bearer sk_live_...' \
-d '{"name":"Ada","role":"admin"}'
# Convert to Python with one click
import requests
response = requests.request('POST', url,
headers=headers, json=payload)
Paste anything. We’ll figure it out.
Popular tools
For your privacy, this site runs without servers — your workspace (snippets, favorites and recent tools) lives only in this browser’s local storage. Download your workspace file to move to another device or to continue after clearing browser data, then restore it here anytime.
JSON Formatter
Paste ugly JSON, get beautifully formatted, syntax-highlighted output with collapsible sections.
VALIDATE + FORMATJWT Decoder
Decode JSON Web Tokens. Inspect header, payload, and signature. Verify expiration and claims.
NO SERVERcURL Converter
Convert cURL commands to Python, JavaScript, Node.js, Go, PHP, Ruby, Rust, or C#. Or reverse: code back to cURL.
8 LANGUAGESDiff Checker
Compare two blocks of text side by side. Spot additions, deletions, and changes instantly. Perfect for API responses.
SIDE BY SIDEBase64 Encode / Decode
Instantly encode or decode Base64 strings. Supports text, URLs, and binary-safe operations.
BIDIRECTIONALURL Encode / Decode
Encode special characters for safe URL transmission, or decode percent-encoded strings back to readable text.
QUERY FRIENDLYRegex Tester
Test regular expressions in real-time. See matches, groups, and positions with live highlighting.
LIVE MATCHESTimestamp Converter
Convert Unix epoch timestamps to human-readable dates and vice versa. Supports milliseconds and seconds.
EPOCH ↔ DATEHash Generator
Generate SHA-256, SHA-512, and SHA-1 hashes from any text. Useful for verifying data integrity.
CRYPTO HASHESHTML Entity Encoder
Encode special characters to HTML entities (< → <) or decode them back. Essential for web dev.
ENCODE + DECODECSV ↔ JSON
Convert CSV data to JSON arrays or flatten JSON back to CSV. Handles headers and nested values.
BIDIRECTIONALType Generator
Generate TypeScript, Go, or Python type definitions from any JSON object or array. Paste API response, get types.
JSON → TYPESAPI Request Builder
Build cURL commands visually. Pick method, add headers, set body and auth — then convert to code instantly.
GUI → cURLURL Parser
Break down any URL into protocol, host, path, query params, hash. Rebuild or modify query strings with ease.
DECOMPOSEMock Data Generator
Generate realistic fake JSON data for API testing. Users, products, orders — customize count and fields instantly.
API TESTINGcURL Converter
cURL ↔ Code in 8 languages. Nothing leaves your browser.
# Paste a cURL command on the left and hit Convert
cURL Command Converter — How to Turn cURL into Code in Seconds
The cURL Converter at LocalDevToolbox translates raw cURL commands into ready-to-run code for Python, JavaScript, Go, PHP, Ruby, Rust, C# and Node.js. Developers copy a cURL command from browser developer tools, API documentation or a colleague's message, paste it here, and receive clean, idiomatic code for the language of their choice. Because everything runs locally in your browser with plain JavaScript, your commands — which often contain API keys, tokens and internal endpoints — are never uploaded to a server, logged or shared. There is no signup, no account and no usage limit. The conversion engine understands headers, cookies, request bodies, query parameters, authentication flags and multipart uploads, so even complex real-world commands convert accurately. You can also run the conversion in reverse, turning source code back into a cURL command for quick testing.
Working entirely client-side means you can use the converter on corporate machines, with confidential staging APIs or inside restricted networks where pasting commands into online services would be a security risk. Results appear instantly as you type, and a copy button puts the generated code on your clipboard in one click. Whether you are building SDKs, writing integration tests or just want to escape cURL syntax forever, this free browser-based tool keeps your workflow fast and your data private. Everything runs in a single lightweight page that loads fast even on slow connections, and because no state is kept server-side, closing the tab removes every trace of what you converted.
How can I convert a cURL command to Python without uploading it anywhere?
Paste your cURL command into this tool and select Python. The conversion runs entirely in your browser using JavaScript, so the command never leaves your device — nothing is sent to a server, stored or logged. You can verify this by disconnecting from the internet after the page loads: the converter keeps working.
Is this cURL converter free and does it require an account?
Yes, it is completely free with no signup, no account and no usage limits. There is no premium tier and no hidden cost — the tool works instantly in any modern browser on desktop and mobile.
JSON Formatter
Paste ugly JSON, get beautifully formatted output with syntax highlighting.
JSON Formatter and Validator — Beautify Messy JSON Instantly
The JSON Formatter cleans up minified, malformed or deeply nested JSON and presents it as a readable, syntax-highlighted tree. Paste an API response, a config file or a snippet from a log file, and the formatter validates the structure in real time, pointing out exactly where the syntax breaks if the document is invalid. Collapsible nodes let you expand and collapse objects and arrays, which makes exploring large payloads — such as search results or complex REST responses — far easier than scrolling through raw text. Everything is processed locally in your browser with zero network requests, so sensitive configuration data, customer records or internal API responses stay on your machine. There is no file size quota imposed by a server, no queue and no account requirement; the tool simply runs as fast as your browser allows.
Developers use the formatter to debug broken JSON, prepare examples for documentation, compare payloads before and after a change, or make a single-line API response human-readable in seconds. Because your data never travels to a server, the tool is safe for production configs, unpublished API responses and any data covered by privacy policies or NDAs. Since the formatter never sees your data, it also doubles as a safe way to share formatting steps with teammates: everyone opens the same URL, pastes locally, and gets identical results without a single byte crossing the network.
How can I validate JSON online without my data being stored?
Paste your JSON into this formatter. Validation happens locally in your browser — the text is never transmitted to any server. You can confirm this by loading the page, disconnecting from the internet and formatting again: it still works, which proves no data leaves your device.
Can I format large JSON files with this tool?
Yes. Because there is no server upload step, the practical limit is your device's memory rather than an upload cap. JSON payloads of several megabytes format instantly on a modern laptop, with no queue and no waiting.
JWT Decoder
Decode JSON Web Tokens. Inspect header, payload, and signature locally.
JWT Decoder — Inspect Tokens Locally Without Sending Them Anywhere
The JWT Decoder splits any JSON Web Token into its three parts — header, payload and signature — and displays them as readable, syntax-highlighted JSON. It automatically detects and shows standard claims such as iss, sub, aud, exp and iat, converts the expiration timestamp into a human-readable date, and warns you when a token has already expired. All of this happens entirely in your browser. JWTs are credentials: they grant access to accounts, APIs and paid services, which is why pasting them into random online decoders is a genuine security risk. LocalDevToolbox runs the decoding with plain JavaScript on your device, so the token — and whatever access it represents — is never exposed to a third party. No signup, no network call, no storage: the token is processed the moment you paste it and disappears when you close the tab.
This makes the decoder suitable for debugging authentication flows, inspecting tokens from staging environments and checking claim values during development — even on machines with strict security policies. You get instant results with zero configuration, and nothing you paste is logged anywhere. A color-coded validity indicator, copy buttons for each decoded section and support for both compact and pretty-printed output make it a practical everyday utility rather than a debugging chore.
Is it safe to paste a JWT into an online decoder?
Usually not — a token is a credential, and pasting it on a server-based tool exposes it to whoever operates that server. This decoder works locally in your browser, so the token never leaves your device. After loading the page you can even disconnect from the internet and it keeps decoding.
How do I check when a JWT expires?
Paste the token here and look at the exp claim in the payload section. The decoder converts the Unix timestamp into an exact date and time and indicates whether the token is still valid or already expired.
Base64 Encode / Decode
Encode text to Base64 or decode Base64 back to text. All processing happens locally.
# Result appears here
Base64 Encoder and Decoder — Instant, Private Text Conversion
The Base64 tool encodes plain text into Base64 format and decodes Base64 strings back to readable text, instantly and entirely in your browser. Base64 is everywhere in modern development: it appears in HTTP headers, Basic authentication, data URIs for images, JWT payloads, email attachments and configuration files. This tool handles all of those everyday cases without requiring you to trust an online service with potentially sensitive content — credentials, tokens and internal data are processed on your device and never uploaded. Encoding and decoding run character by character in JavaScript as you type or paste, with no submit button, no page reload and no server round-trip. The tool also handles URL-safe Base64 variants and binary-safe input, so developer payloads from headers, cookies and APIs decode cleanly.
Because the conversion is local, you can safely use it for Basic Auth header construction, debugging data URIs, extracting payload text from tokens or preparing test fixtures — even on locked-down corporate machines. It is free, requires no account and works offline once the page is loaded. Everything runs in a single lightweight page that loads fast even on slow connections, and because no state is kept server-side, closing the tab removes every trace of what you converted.
How can I encode text to Base64 without a server?
Type or paste your text here and the Base64 output appears immediately. The conversion runs completely in your browser with JavaScript — nothing is sent to a server or stored anywhere. Disconnect from the internet after loading the page and it will still encode and decode, proving it works locally.
What is the difference between standard and URL-safe Base64?
Standard Base64 uses + and / characters, which have special meanings in URLs. URL-safe Base64 replaces them with - and _ so the encoded value can sit safely in query strings, cookies and tokens. This tool handles both variants automatically.
URL Encode / Decode
Encode special characters for safe URL transmission, or decode percent-encoded strings.
# Result appears here
URL Encoder and Decoder — Safe Percent-Encoding in Your Browser
The URL Encoder converts special characters — spaces, accents, symbols and reserved characters like & and = — into percent-encoded form so strings travel safely inside query parameters, path segments and redirects. Its decoder reverses the process, turning percent-encoded text back into readable form. Web developers reach for this constantly when building query strings by hand, debugging redirect chains, constructing OAuth callbacks or cleaning up URLs copied from emails and documents. Everything here runs client-side in your browser: the strings you encode may contain session IDs, internal hostnames or personal data from URLs, and none of it is transmitted, logged or stored on any server. Results update instantly as you type, with no submit button and no page reload. Both directions are available from the same page, so decoding a captured request and re-encoding the fixed value takes seconds, not tool switches.
The tool follows the same encoding rules your browser and standard libraries use, so output is fully compatible with fetch, cURL, HTTP clients and every web framework. It is free, needs no account, and works entirely offline after the page loads — a reliable companion for API work, SEO tasks and everyday debugging. The encoder never round-trips your input through a backend, so API keys and session identifiers that happen to sit inside the strings you paste remain under your control at all times.
How do I encode a query parameter that contains spaces and symbols?
Paste the raw value into the encoder and copy the percent-encoded result — spaces become %20 or +, and reserved characters like & and = become %26 and %3D. Use the encoded value in your query string. The whole process runs in your browser, so the data never leaves your device.
Why does my URL break when I paste special characters into it?
URLs only allow a limited set of characters; anything else must be percent-encoded. Raw &, #, spaces or non-ASCII characters are misread by servers or truncated by browsers. Encoding the value first guarantees it survives the trip intact.
Regex Tester
Test regular expressions in real-time. See matches, groups, and positions.
Regex Tester — Try Regular Expressions with Live Highlighting
The Regex Tester evaluates a regular expression against your test text in real time, highlighting every match, captured group and position as you type. It supports the standard JavaScript regex syntax with all common flags — case-insensitive matching, multiline mode, dot-all and Unicode — making it a faithful preview of how your pattern will behave in Node.js or the browser. Building and debugging regex is famously error-prone, and a live tester saves the trial-and-error cycle of editing code, rerunning scripts and printing results. Because the tool evaluates patterns locally, the text you test against — which might be log excerpts, sample customer data or proprietary formats — never leaves your machine. There is no server round-trip: matching runs on every keystroke directly in your browser.
Use it to build validation rules for forms, craft extraction patterns for logs, tune search-and-replace expressions or teach yourself regex with immediate visual feedback. It is free, requires no signup and keeps your test data completely private. A built-in cheat sheet of common patterns for emails, dates, numbers and URLs helps you start from a working example instead of a blank input, and every match count updates live as the pattern evolves.
How can I test a regular expression online without exposing my data?
Type your pattern and sample text here — matching runs entirely in your browser with JavaScript. The test text is never sent to a server, so you can safely use real log excerpts or sample data. After the page loads you can go offline and the tester keeps working.
Which regex flavor does this tester use?
It uses JavaScript's built-in regular expression engine, the same one that powers Node.js and browser code. If your pattern works here, it will behave identically in your JavaScript code, including capture groups, flags and lookarounds.
Timestamp Converter
Convert between Unix epoch timestamps and human-readable dates.
Timestamp Converter — Translate Epoch Time to Human Dates
The Timestamp Converter translates Unix epoch timestamps — the seconds or milliseconds since January 1, 1970 — into readable dates and times, and converts any calendar date back into epoch form. It auto-detects whether your value is in seconds or milliseconds, shows the result in your local timezone as well as UTC, and updates live as you type. Epoch values appear constantly in developer work: JWT exp and iat claims, API response fields, database columns, log lines, cache headers and webhook payloads all carry timestamps in this numeric form. Converting them by hand or with a spreadsheet is slow; this tool gives the answer instantly. And because everything is computed locally in your browser, timestamps from production systems — which can leak internal information — are never sent to a server.
The converter is equally useful for checking token expiration, verifying webhook delivery times, comparing log entries across timezones or generating a timestamp for a test fixture. No signup, no limits, and it keeps working even with your internet connection off. Batch-style workflows benefit too: developers keep the page open in a tab and paste values from logs or headers as they appear, with the answer rendered before their hand leaves the keyboard.
How do I convert a Unix timestamp to a readable date?
Paste the number into the converter. It automatically detects seconds or milliseconds and shows the exact date and time in your local timezone and UTC. The calculation happens locally in your browser — the timestamp is never uploaded anywhere.
What is the difference between seconds and milliseconds in epoch timestamps?
Both count time since January 1, 1970 — seconds are ten digits (for example 1719000000) while milliseconds are thirteen digits (1719000000000). This tool recognizes both formats automatically and labels which one it detected.
Hash Generator
Generate cryptographic hashes from any text using SHA-256, SHA-512, or SHA-1.
# Hash appears here
Hash Generator — Create SHA-256, SHA-512 and SHA-1 Checksums
The Hash Generator computes cryptographic digests of any text using SHA-256, SHA-512 or SHA-1 via the browser's native Web Crypto engine. Hashes serve as fingerprints: a single changed character produces a completely different digest, which makes hashing ideal for verifying file integrity, comparing configurations, detecting duplicate records and generating deterministic keys. Because hashing runs on your device through the Web Crypto API, the input — a password in testing, a secret from a config file, sample customer data — is never transmitted to a server. Many online hash tools quietly log inputs; this one physically cannot, since no network request ever carries your text. Results appear as soon as you finish typing, with no submit button and no page reload.
SHA-256 is the default choice for modern integrity checks, SHA-512 offers a larger digest, and SHA-1 remains useful for legacy compatibility. The tool is free, account-free and works offline once loaded, making it safe to use in security-sensitive environments. Developers comparing two config versions often paste both and hash them side by side in seconds — something that would otherwise require command-line tools or trusting a web form with sensitive values.
How can I hash text online without the tool seeing my data?
Type or paste the text here and the digest is computed by your browser's built-in Web Crypto engine. No request is sent anywhere, so the input cannot be logged by a third party. You can disconnect from the internet after loading the page and hashing continues to work.
Which hash algorithm should I use — SHA-256, SHA-512 or SHA-1?
Use SHA-256 for most integrity checks; it is fast, widely supported and considered secure. SHA-512 produces a longer digest for specialized uses, while SHA-1 is deprecated for security purposes and should only be used for legacy compatibility.
HTML Entity Encoder
Encode special characters to HTML entities or decode them back to plain text.
# Result appears here
HTML Entity Encoder and Decoder — Safe Character Escaping
The HTML Entity Encoder converts special characters into their HTML entity form — ampersands into &, quotes into ", angle brackets into < and > — and decodes entities back to plain text. This matters wherever untrusted or special content is rendered on a web page: encoding user input is the foundation of XSS prevention, and displaying code snippets in documentation or blog posts requires entity-escaping to keep the browser from interpreting the markup. The tool processes everything locally in your browser, so the text you encode — which may contain payloads, credentials or unpublished code — is never uploaded to a server. Encoding and decoding happen instantly as you type, with bidirectional conversion available in one click. Both directions are available from the same page, so decoding a captured request and re-encoding the fixed value takes seconds, not tool switches.
Beyond security work, the tool helps when pasting text from Word or PDFs into CMS editors, cleaning up exported HTML, or preparing email templates where raw special characters break rendering. It is free, needs no account and runs fully offline once the page has loaded. Developers reviewing pull requests use it to encode sample payloads for tests, and content teams rely on it when rich text from office documents breaks page layouts after publishing.
How do I prevent XSS when displaying user input in HTML?
Encode every special character — especially angle brackets, ampersands and quotes — into HTML entities before inserting the value into the page. This tool performs that encoding instantly and locally: paste the input, copy the encoded output, and no untrusted markup can execute. Nothing is sent to any server.
Why do I see strange codes like & or < in web pages?
Those are HTML entities — safe text representations of reserved characters. Browsers display them as normal characters while treating them as plain text, never as markup. They appear whenever a page needs to show code samples or characters that would otherwise break the HTML structure.
CSV ↔ JSON
Convert CSV data to JSON arrays or flatten JSON back to CSV format.
# Result appears here
CSV to JSON Converter — Two-Way Conversion with Nested Support
The CSV ↔ JSON Converter transforms spreadsheet-style CSV data into JSON arrays and flattens JSON back into CSV, handling headers, quoted fields with commas and nested object values. It is the bridge between the two formats that dominate data exchange: CSV, the lingua franca of Excel, exports and legacy systems, and JSON, the native format of modern APIs and NoSQL databases. Paste a CSV export from a CRM, a database dump or a spreadsheet and receive a typed JSON array ready for an API payload or a script; or take a JSON response and get a flat CSV for analysis in a spreadsheet. All conversion runs locally in your browser — customer lists, revenue figures or any confidential export is processed on your machine and never uploaded, which matters when company policy forbids pasting data into online converters.
Header detection runs automatically, and nested JSON values are serialized sensibly on the way to CSV. The tool is free, requires no signup, imposes no row limits beyond your device's memory and keeps working offline after the first load. The two-way design means a single page covers both directions of the workflow — export from a legacy tool to JSON for a modern pipeline, then back to CSV for the analyst who lives in spreadsheets.
How can I convert CSV to JSON without uploading my spreadsheet?
Copy the CSV content and paste it here — the parser runs entirely in your browser. No file upload step exists, so your data never touches a server. This makes the tool safe for customer lists, financial exports and any data covered by privacy requirements.
Does the converter handle CSV fields that contain commas and quotes?
Yes. It follows standard CSV parsing rules: quoted fields may contain commas, quotes are escaped by doubling them, and line breaks inside quotes are preserved. Headers are detected from the first row and used as JSON keys.
Type Generator
Generate TypeScript, Go, or Python type definitions from any JSON object or array.
# Paste JSON and hit Generate
Type Generator — Turn JSON into TypeScript, Go and Python Types
The Type Generator reads any JSON object or array and produces matching type definitions — TypeScript interfaces, Go structs or Python type hints — inferred directly from the data's shape. Paste a sample API response and get production-ready types with correct field names, optional markers where values are missing and nested structures fully expanded. This eliminates the tedious manual work of translating a JSON payload into typed models and, more importantly, prevents the drift that happens when types are written by hand and the API quietly changes. Inference runs entirely in your browser: API responses from internal services, which often contain real customer data or unreleased endpoints, are analyzed on your device and never sent anywhere. There is no account, no quota and no waiting.
The generator is perfect for bootstrapping SDK models, typing a new integration quickly, or documenting an API's response shape for teammates. Output copies to your clipboard in one click and pastes cleanly into any codebase. Teams standardizing on typed codebases run sample responses through the generator during code review, turning 'does this type match reality?' into a five-second check instead of an afternoon of diff-reading. Because inference happens locally, nothing about your API — not even its shape — is disclosed to outside services.
How do I generate TypeScript types from an API response?
Send the request, copy the JSON response body and paste it here with TypeScript selected. The generator infers interfaces from the actual values — strings, numbers, booleans, arrays and nested objects — and emits typed definitions instantly, all locally in your browser.
Is it safe to paste a real API response into this tool?
Yes. The response is parsed and analyzed entirely on your device; no part of it is transmitted to a server. This makes the tool suitable even for responses containing production data or secrets from internal endpoints.
API Request Builder
Build cURL commands visually. Then convert to code with one click.
# Fill the form and hit Build cURL
API Request Builder — Construct cURL Commands Visually
The API Request Builder replaces memorized cURL flags with a visual form: choose the HTTP method, set the endpoint URL, add headers row by row, write a JSON or form body, configure basic authentication or bearer tokens — and watch a correct, properly escaped cURL command assemble itself in real time. The generated command can be copied straight into a terminal or documentation, and the same request converts into code through the built-in cURL converter. This is invaluable when documenting endpoints for teammates, reproducing a frontend request in the terminal, or building requests with many headers where hand-typed cURL inevitably picks up escaping mistakes. Everything happens in your browser: endpoint URLs, bearer tokens and request bodies from private APIs stay on your machine and are never transmitted to or stored on any server.
Because there is no backend, you can safely build requests against internal hostnames and staging environments, even on networks that block external API tools. The builder is free, needs no account and produces valid cURL on every keystroke. Teams documenting internal APIs keep it open during writing sessions: fill the form once, paste the generated command into the docs, and every example is guaranteed to be syntactically valid. The form remembers nothing between visits, which is exactly what you want when working with production credentials.
How can I build an API request without using an online API client?
Fill in the method, URL, headers, body and auth fields here and a valid cURL command is generated instantly in your browser. Unlike cloud API clients, no request data leaves your device — you can even disconnect from the internet after the page loads and keep building.
How do I add a bearer token to the generated cURL command?
Choose Bearer Token in the authentication section and paste your token. The builder adds a correctly formatted Authorization header to the command. The token is only processed locally in your browser and is never sent anywhere.
Diff Checker
Compare two blocks of text side by side. Spot additions, deletions, and changes instantly.
Diff Checker — Compare Two Text Blocks Side by Side
The Diff Checker compares two blocks of text line by line and highlights exactly what changed: added lines, removed lines and modified sections, presented in a clear side-by-side view. It answers the everyday developer question — what exactly changed between these two versions? — in seconds, without installing anything. Typical uses include comparing configuration files before and after an edit, reviewing an API response that suddenly behaves differently, checking a SQL dump against its backup, or reviewing a document against the previous version. Because the comparison runs entirely in your browser, the content you diff — production configs, database excerpts, proprietary code — is never uploaded to a third-party service. Many online diff tools transmit both texts to a server; this one keeps everything on your device, with no account and no length limit beyond your own memory.
Results appear as you type or paste, so iterating on a fix is immediate. The tool is free, works on desktop and mobile, and requires nothing more than a modern browser. There is nothing to configure: no diff algorithm options to learn, no ignore-whitespace checkboxes buried in settings — paste two texts and the answer is on screen before you reach for the mouse. The whole comparison stays in memory on your device for the duration of the session.
How can I compare two files without uploading them?
Open each file, copy its contents and paste the two versions into the left and right fields. The comparison runs locally in your browser — the text is never transmitted, which makes the tool safe for confidential configs, code and documents.
What do the colors in the diff output mean?
Added lines are shown in green, removed lines in red, and changed sections are shown with the exact character differences highlighted. This makes it easy to spot a single edited value inside a large block of text.
URL Parser
Break down any URL into components. Rebuild or modify query strings with ease.
URL Parser — Break Any URL into Its Parts Instantly
The URL Parser decomposes any URL into its components — protocol, host, subdomain, domain, port, path segments, query parameters and fragment — and displays each piece in a clean, labeled list. Query strings are parsed into individual key-value pairs that you can inspect, copy or edit, which turns an opaque twenty-parameter tracking URL into a readable table. Developers use it to debug redirect chains, inspect OAuth callbacks, understand how a CMS builds its URLs, or extract UTM parameters for analysis. The parser runs entirely in your browser's native URL engine, so every URL you inspect — including signed URLs with secrets in the query string, internal hostnames or pre-release links — stays on your device and is never logged by a server. Results update as you type, with no submit and no reload.
It also validates malformed URLs and shows which part fails to parse, a handy first step when debugging 404s or routing issues. Free, no signup, fully private and offline-capable once loaded. Because nothing is uploaded, the parser is routinely used on pre-signed cloud storage URLs and webhook verification links whose query strings contain secrets that must never leave the developer's machine. The parsed components can be copied individually when you need just the host or a single parameter.
How do I extract query parameters from a URL?
Paste the full URL into the parser. Every query parameter is split into a key-value pair and listed separately, ready to inspect or copy. The parsing happens locally in your browser, so even signed URLs with secrets in the query string are never sent anywhere.
What parts does a URL consist of?
A URL has a protocol (https), a host made of subdomain, domain and optional port, a path with segments, an optional query string starting with a question mark, and an optional fragment after the hash sign. The parser shows all of these separately so you can see exactly how the URL is constructed.
Mock Data Generator
Generate realistic fake JSON data for API testing. Customize count and schema instantly.
Mock Data Generator — Realistic Fake JSON for API Testing
The Mock Data Generator produces realistic fake JSON for testing: user profiles with names and emails, products with prices and SKUs, orders with statuses and totals, and more — all generated locally in your browser. Front-end developers constantly need data that looks real enough to design against but contains zero genuine personal information. Instead of copying records from production, which is a privacy violation waiting to happen, or hand-writing twenty JSON objects, you choose a preset, set the count and receive varied, well-structured data instantly. Because generation runs on your device with no network calls, the output is safe to commit to repositories, paste into issue tickets or embed in documentation. Values are randomized on every generation, giving you fresh datasets each time.
The tool shines when building user interfaces before the backend exists, writing demos, populating test databases or load-testing serializers with realistic payloads. It is free, requires no account and imposes no generation limits beyond your browser's memory. Every generated document follows consistent field naming, so fixtures look professionally authored rather than random — reviewers can tell at a glance that the data is synthetic and safe. No two runs produce the same dataset, so screenshots and demos never accidentally reuse identical values.
How can I generate test data without exposing real user information?
Use this generator instead of sampling production data. Every record is synthesized locally in your browser from random values — no real names, emails or addresses are involved, and nothing is sent to a server. The generated JSON is safe to share, commit and publish.
Can I control how many records are generated?
Yes. Pick a preset, enter the desired count — from a handful of rows to thousands — and the generator produces that many randomized records instantly, all on your device with no rate limits.
Developer Toolbox Guide
Complete reference for all 15 tools. What they do, when to use them, and how they work.
What is LocalDevToolbox?
LocalDevToolbox is a free, browser-based developer utility suite containing 15 powerful tools. Every operation runs entirely in your browser using JavaScript — no data ever leaves your device. There is no server, no tracking, and no cookies.
This guide explains what each tool does, common use cases, and the underlying algorithms. All tools are available instantly without registration.
🔄 cURL Converter
Parses cURL commands and converts them to Python (requests), JavaScript (fetch), Node.js (axios), Go, PHP, Ruby, Rust, or C# code. Also supports reverse conversion from code back to cURL. Uses a custom tokenizer to handle quoted strings, flags, headers, form data, and multipart uploads.
📋 JSON Formatter
Validates and pretty-prints JSON with syntax highlighting and collapsible tree view. Uses native JSON.parse() for validation. Supports minification and path-based node toggling.
🔐 JWT Decoder
Splits JSON Web Tokens into Header, Payload, and Signature components using Base64URL decoding. Displays claims like exp, iat, iss with expiration status. No signature verification (no secret key required).
🔤 Base64 Encode / Decode
Uses browser-native btoa() and atob() with UTF-8 safe encoding via encodeURIComponent. Handles text, URLs, and binary-safe operations in both directions.
🔗 URL Encode / Decode
Wraps encodeURIComponent() and decodeURIComponent(). Essential for preparing query strings, form data, and API parameters. Handles special characters, spaces, and Unicode.
🔍 Regex Tester
Compiles JavaScript RegExp objects with configurable flags (g, i, m, s). Shows all matches, capture groups, and positions in real-time. Useful for email validation, log parsing, and pattern extraction.
⏱️ Timestamp Converter
Converts between Unix epoch timestamps (seconds or milliseconds) and human-readable ISO/local dates. Uses native Date object. Includes "Use now" button for instant current timestamp.
#️⃣ Hash Generator
Generates SHA-256, SHA-512, and SHA-1 hashes using the Web Crypto API (crypto.subtle.digest). Useful for verifying file integrity, password hashing comparisons, and checksum generation.
📝 HTML Entity Encoder
Encodes special characters to HTML entities and decodes them back. Uses a temporary DOM textarea for accurate entity mapping. Essential for XSS prevention and HTML content generation.
📊 CSV ↔ JSON
Converts comma-separated values to JSON arrays and vice versa. Handles header rows, simple escaping, and basic nested structures. Useful for data migration, spreadsheet exports, and API payload preparation.
🏷️ Type Generator
Infers type definitions from JSON objects and generates TypeScript interfaces, Go structs, or Python classes. Recursively analyzes nested objects and arrays. Perfect for API integration when you only have sample responses.
🛠️ API Request Builder
Visual form for constructing cURL commands with method, URL, headers, body, and authentication. Outputs raw cURL that can be fed directly into the cURL Converter. Supports Basic Auth and Bearer tokens.
📑 Diff Checker
Compares two text blocks using a line-based LCS (Longest Common Subsequence) algorithm. Highlights additions, deletions, and inline character changes. Ideal for comparing API responses, config files, or code snippets.
🌐 URL Parser
Decomposes any URL into protocol, host, port, pathname, query parameters, and hash using the native URL constructor. Displays query params as a clean key-value list.
🎲 Mock Data Generator
Generates realistic fake JSON data for API testing. Includes templates for Users, Products, Orders, Blog Posts, Companies, and Employees. Supports custom field definitions. All data is generated locally using Math.random() — no external APIs called.
Developer Toolbox Guide — Every Tool Explained with Use Cases
This guide is the complete reference for LocalDevToolbox's fifteen browser-based developer tools. Each entry explains what the tool does, the concrete problems it solves and the situations where it earns its place in your workflow — from converting cURL commands into code for a new integration, to formatting a malformed JSON response in the middle of a debugging session, to decoding a JWT while tracing an authentication bug. Every tool shares the same philosophy: they run entirely in your browser, send nothing to a server, require no account and keep working even when your connection drops. That makes the whole toolbox safe for confidential work — production configs, tokens, customer data and internal endpoints can be processed without a second thought about where they might end up.
Whether you are a backend developer, front-end engineer, student or site reliability engineer, the guide helps you discover the right tool for the task at hand and explains the concepts behind it in plain language. Bookmark it and skip the next ten-plugin install ritual. The index at the top of the page jumps straight to each tool's section. New tools join the box over time, and each one follows the same rule: useful in ten seconds, trustworthy with your most sensitive data, and gone from your machine the moment you close the tab.
Are all LocalDevToolbox tools really free and private?
Yes. All fifteen tools are free with no signup, no usage limits and no premium tier. Every tool runs locally in your browser, so your data never reaches a server — you can verify this by disconnecting from the internet after the page loads and watching everything keep working.
Do I need to install anything to use these developer tools?
No installation is needed — every tool works in any modern browser on desktop or mobile. There are no extensions, no desktop apps and no dependencies; open the page and start working immediately, even offline after the first visit.