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Developer Tools

Free, browser-based developer tools for the small but constant tasks that fill a coding day - pretty-printing JSON, decoding a token, encoding a string, testing a regex or converting between data formats. Everything runs locally in your browser tab, so config blobs, payloads and secrets stay on your machine.

No extension to install and no account to create: paste a value, get the result, and copy it straight back into your editor or terminal.

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Base64 Encoder & Decoder

Encode UTF-8 text to Base64 online or decode Base64 back to UTF-8 and plain text. Runs in your browser with no upload.

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Bulk URL Encode / Decode

Encode or decode many URLs at once. Paste a newline-separated list and the tool processes each line in parallel, preserving order and blank lines.

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Code Screenshot

Create beautiful code snippet images with customizable themes.

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Color Converter

Convert colors between HEX, RGB, HSL and CMYK formats.

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Cron Expression Parser

Parse cron expressions into human-readable schedules with next run times.

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CSS Formatter / Minifier

Format, beautify and minify CSS code.

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CSV to JSON Converter

Convert CSV data to JSON array format.

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Diff Checker

Compare code or text with line-by-line diff and unified output.

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Hash Generator

Generate SHA-1, SHA-256, SHA-384 and SHA-512 hashes from text.

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HMAC Generator

Generate HMAC signatures with SHA-1, SHA-256, SHA-384 and SHA-512.

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HTML Entity Encode / Decode

Encode special characters to HTML entities or decode them back.

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HTML Formatter / Beautifier

Format, beautify and minify HTML code.

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HTML to JSX Converter

Convert HTML to JSX with automatic attribute conversion.

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HTTP Status Code Reference

Searchable reference for all HTTP status codes with descriptions.

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JavaScript Formatter / Minifier

Format, beautify and minify JavaScript code with Prettier-style defaults.

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JSON Diff Viewer

Compare two JSON documents semantically. Detects added, removed and changed keys and array elements; ignores object key order.

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JSON Formatter

Format, validate and minify JSON with syntax highlighting.

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JSON to CSV Converter

Convert JSON arrays to CSV format with custom delimiters.

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JSON to YAML Converter

Convert JSON to YAML format instantly.

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JSONPath Evaluator

Run JSONPath queries against a JSON document and see the matched values. Supports child, index, slice, wildcard and recursive-descent operators.

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JWT Decoder

Decode and inspect JWT tokens — header, payload and claims.

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JWT Token Generator

Sign a JWT (HS256, HS384, HS512) from a JSON payload and shared secret. Runs entirely in your browser using the Web Crypto API.

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Markdown Preview

Write Markdown and see rendered HTML in a live split-pane preview.

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MIME Type Lookup

Look up MIME types by file extension or search by type.

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Regex Tester

Test regular expressions with live highlighting, matches and capture groups.

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SQL Formatter

Format and beautify SQL queries with keyword uppercasing.

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Tailwind CSS Playground

Write HTML with Tailwind CSS classes and see live results. Use it as an online Tailwind editor and Tailwind play environment.

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TOML to JSON Converter

Convert TOML configuration to JSON format.

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Unix Timestamp Converter

Convert Unix timestamps to human-readable dates and back.

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URL Encoder / Decoder

Online URL encoder and decoder for query strings, paths, and HTTP request values - percent-encodes characters with encodeURIComponent.

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URL Parser

Break a URL into protocol, host, port, path, query parameters and hash with a structural view of every component.

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User Agent Parser

Parse user agent strings to identify browser, OS and device.

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UUID Generator

Generate UUID v4 identifiers, single or in bulk.

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UUID Version Detector

Identify the version (v1, v3, v4, v5, v6, v7, v8) and variant of any UUID and extract embedded timestamps.

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XML Formatter / Validator

Format, beautify and validate XML with customizable indentation.

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YAML to JSON Converter

Convert YAML to JSON format instantly.

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Format, validate and diff structured data

Working with APIs means staring at structured text all day. The JSON formatter beautifies, minifies and validates JSON so a one-line API response becomes readable, and the JSON diff viewer highlights exactly which keys and values changed between two payloads. Markup and config get the same treatment with the XML formatter, HTML formatter, CSS formatter, JavaScript formatter and SQL formatter. For arbitrary text, the diff checker shows line-by-line changes between any two snippets.

Encode, decode and inspect

Encoding bugs are everywhere, so the Base64 encoder and decoder and the URL encoder and decoder handle the two most common cases, with bulk URL encode/decode for whole lists and HTML entity encode/decode for markup-safe strings. When you need to read what is inside a token, the JWT decoder splits the header and claims so you can check expiry and audience before trusting it, and the JWT token generator creates signed test tokens. The URL parser breaks a link into its scheme, host, path and query parts.

Convert between data formats

Half of integration work is reshaping data. Move between tabular and tree formats with CSV to JSON and JSON to CSV, between config dialects with JSON to YAML, YAML to JSON and TOML to JSON, and into markup with HTML to JSX for React components. The JSONPath evaluator lets you query a nested object with a path expression rather than scrolling through it by eye.

Generate identifiers and signatures

Need values rather than transformations? The UUID generator produces v4 and other identifiers, the UUID version detector tells you which spec an existing UUID follows, the hash generator and HMAC generator create checksums and signatures, and the Unix timestamp converter turns epoch seconds into a human date and back.

Test, parse and reference

Some tools save you a trip to documentation or a scratch script. The regex tester lets you build and verify a pattern against sample input with live match highlighting, the cron expression parser explains a schedule in plain language, and the user agent parser breaks a UA string into browser, OS and device. Quick lookups live in the HTTP status code reference and the MIME type lookup, while the markdown preview and Tailwind playground give you a quick render surface.

Why client-side dev tools matter

Developer payloads frequently contain secrets - bearer tokens, connection strings, customer records inside a sample response, signing keys. Pasting those into a site that round-trips them through a backend means a third party could log them. Every tool in this category runs as JavaScript in your browser, so the data is processed locally and never uploaded. That also makes the tools fast and usable offline once loaded, which is exactly what you want when debugging on a flaky connection or a locked-down network.

  • Local processing - tokens, payloads and keys stay in the tab.
  • No signup - paste and go, nothing is saved between sessions.
  • Chainable - decode Base64, then format the JSON inside it, then diff it.
  • Reference + transform - lookups and converters in one place.

Frequently Asked Questions

Is it safe to paste a JWT or API payload into these tools?

The developer tools here process input in your browser using client-side JavaScript and do not upload it to ZeroUtil. That is safer than tools that decode tokens server-side, but you should still avoid pasting long-lived production secrets into any web page, and rotate anything that may have been exposed. For sensitive test data, open the network panel and confirm no requests are made.

What is the difference between the JSON formatter and the JSON diff viewer?

The JSON formatter beautifies, minifies and validates a single document so it is readable and syntactically correct. The JSON diff viewer compares two JSON documents and highlights which keys and values were added, removed or changed, which is what you want when comparing API responses or config versions.

Can I convert between JSON, YAML, CSV and TOML here?

Yes. There are dedicated converters for CSV to JSON, JSON to CSV, JSON to YAML, YAML to JSON and TOML to JSON. Each runs in the browser, so you can reshape config files and data exports without uploading them, and you can chain conversions - for example CSV to JSON, then JSON to YAML.

Do the developer tools work offline?

Once the page has loaded, the formatters, encoders, converters and generators run entirely client-side, so most continue to work without a connection. This is possible because none of them depend on a backend request to do their core job, which also keeps them fast on large inputs.

How do I test a regular expression online?

Open the regex tester, enter your pattern and flags, and paste sample text below it. Matches are highlighted live as you edit the pattern, so you can refine a regex against real input before dropping it into code. Like the other tools, it runs in your browser and does not send your test data anywhere.