FastDevTool

Paste messy developer data, fix it fast, and keep it in your browser. Start with JSON, JWT, Base64, Regex, or Text Diff.

JSON Formatter JSON to CSV JSON Validator JSON Viewer JWT Decoder Regex Tester

Private JSON tools for developer workflows

FastDevTool focuses on the jobs developers search for most often: formatting API responses, converting JSON to CSV, validating config files, and exploring nested payloads.

Debug API payloads

Paste a response, format it, validate the syntax, and inspect nested fields without uploading private data.

Open JSON Formatter

Move JSON into spreadsheets

Convert arrays of objects into CSV columns for Excel, Google Sheets, BI imports, and quick data reviews.

Convert JSON to CSV

Fix parse errors

Catch trailing commas, missing quotes, broken brackets, and escaped string issues before code or APIs fail.

Validate JSON

Why FastDevTool?

Built with the same tech stack as VS Code. Every tool runs entirely in your browser.

⌨️

Monaco Editor

VS Code's editor engine — syntax highlighting, error squiggles, code folding, ⌘F search.

🔗

Shareable URLs

Share your JSON/code via URL. Data is compressed client-side with pako — zero server cost.

📂

Drag & Drop

Drop any file directly onto the editor to load it instantly. No upload, no server.

🕐

Local History

Your last 10 inputs are saved in the browser. Pick up where you left off, no account needed.

📱

PWA — Works Offline

Install to your home screen. Cached locally so it works even without internet.

🗂️

Multi-Tab Workspace

Open multiple tools side-by-side without losing your work. Built with Zustand.

⚡

100% Client-Side

All processing runs in your browser. Nothing is sent to a server — your data stays private.

🌙

Dark / Light Mode

Full dark mode support across every tool, including the Monaco editor.

All Tools

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JSON Formatter

Format, validate, and minify private JSON in your browser

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JSON Validator

Find JSON syntax errors with line and column hints

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JSON Minifier

Compact JSON for APIs, configs, and embeds

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JSON Viewer

Explore nested JSON as a collapsible tree

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JSON to XML

Convert JSON to XML format

XML to JSON

Convert XML to JSON format

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JSON to YAML

Convert JSON to YAML

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YAML to JSON

Convert YAML to JSON

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JSON to CSV

Convert JSON arrays to spreadsheet-ready CSV

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CSV to JSON

Convert CSV to JSON

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JSON Compare

Diff two JSON objects

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JSON Escape

Escape/unescape JSON strings

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JSON to String

Stringify JSON for embedding

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JSON Schema

Validate JSON against JSON Schema

HTML Formatter

Format and beautify HTML

HTML Minifier

Minify HTML markup

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CSS Formatter

Format and beautify CSS

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CSS Minifier

Minify CSS files

JS Beautifier

Format JavaScript code

JS Minifier

Minify JavaScript

HTML to Text

Strip HTML tags, get plain text

Markdown to HTML

Convert Markdown to HTML

Base64

Encode and decode Base64

URL Encoder

URL encode and decode

URL Decoder

Decode percent-encoded URLs

HTML Encoder

HTML entity encode/decode

HTML Decoder

Decode HTML entities

HTML Escape

Escape HTML special characters

XML Escape

Escape XML special characters

SQL Escape

Escape strings for SQL queries

JS Escape

Escape JavaScript strings

XML Formatter

Format and beautify XML

XML Validator

Validate XML syntax

YAML Formatter

Format YAML configuration

YAML Validator

Validate YAML syntax

SQL Formatter

Format SQL queries

TOML to JSON

Convert TOML to JSON

Regex Tester

Test regular expressions

UUID Generator

Generate UUID v4

Hash Generator

MD5, SHA-1, SHA-256 hashes

Cron Builder

Build cron expressions

JWT Decoder

Decode JWT tokens

jq Playground

Query JSON with jq

Word Counter

Count words and characters

String Utilities

Uppercase, lowercase, reverse, trim

+/-

Text Diff

Compare two texts line by line

Lorem Ipsum

Generate placeholder text

Case Converter

Convert naming conventions

Line Sorter

Sort lines alphabetically

Remove Duplicates

Remove duplicate lines

Color Converter

Convert HEX, RGB, HSL colors