Developer Toolbox | Browser Kitty

Operation demo See the basic workflow in a short video.

About this tool

Developer Toolbox brings 33 small utilities used during everyday development into one local-first interface, including Base64, URL, JSON, JWT, cron, regex, hashes, UUIDs, CIDR calculations, and more.

Smart Input can inspect pasted content and suggest suitable tools, while supported utilities can pass results directly into another tool without manual copy and paste. Input data is not sent to Browser Kitty servers, and working values are generally kept only in memory for the current tab session.

Good for

Quickly encode or decode Base64, URLs, Unicode, Hex, and similar formats
Format or compare JSON/YAML/CSV, inspect JWT payloads, or check upcoming cron execution times
Use regex, UUID, hash, HMAC, UNIX timestamp, CIDR, and other helpers during development
Chain small transformations together without jumping between multiple utility sites

What it can do

Key capabilities available in this tool.

33 developer utilities in one app
Smart Input suggests tools based on pasted content
Send results directly into another tool
Ctrl / Cmd + K search with English and Japanese aliases
Real-time conversion for lightweight tools

How to use

Open the tool and paste a value into Smart Input, or choose a utility from the catalog.
Enter the value into the appropriate Base64, JSON, JWT, cron, regex, or other utility. Lightweight tools update in real time.
Review the result, then copy it, swap input and output where supported, or send the result directly to another tool.
Favorite frequently used utilities and open them quickly with the Ctrl/Cmd + K command palette using English or Japanese aliases.

Supported

Encode: Base64, URL, HTML Entity, Unicode, Hex, and Data URI
Data / Text: JSON, YAML, CSV, JSON Diff, JSONPath, case conversion, line sorting/deduplication, character/byte counts, and escaping
Time / Security: UNIX Timestamp, ISO 8601, date difference, cron, JWT Decoder, hashes, HMAC, and random generation
Developer / Web: regex, UUID, URL Parser, HTTP Status, number bases, CIDR, color conversion, px/rem, and CSS tools

Limitations and notes

JWT Decoder displays the header and payload but does not verify the signature.
Cron targets the common five-field format and calculates upcoming times in the device's local timezone, so behavior can differ from a specific cron implementation.
JSONPath and the YAML parser are lightweight subset implementations rather than complete implementations of every specification feature.
File hashing reads the full file into browser memory, so very large files can use substantial memory. Working input is cleared when the page is reloaded or the tab is closed.

Frequently asked questions

What utilities are included?

It includes 33 common developer utilities covering Base64, URLs, JSON, YAML, CSV, JWT, cron, regex, UNIX timestamps, hashes, HMAC, UUIDs, CIDR, and more.

Are JSON, JWTs, or other inputs sent to a server?

No. Conversion, parsing, inspection, and hashing run locally in the browser, and tool inputs are not sent to Browser Kitty servers.

Does the JWT tool verify signatures?

No. JWT Decoder is for inspecting the header and payload; it does not verify the token signature. Handle tokens containing sensitive information with care.

Are my working values saved in the browser?

Working inputs and outputs are generally kept only in memory and disappear on reload or tab close. Only language settings and favorite tool IDs are stored persistently.

Offline version and source code

The standalone developer-toolbox.html has no third-party runtime library or external API dependency. Save it from GitHub and open it locally to use the utilities without a network connection.

View source on GitHub

Use together

Useful next steps and companion tools, organized around the workflow.