The person behind Toolbit
Toolbit is a personal project by Javier Vallejo, a software developer. It started from a simple, specific need: having fast, trustworthy technical calculators on hand — subnetting, VLSM, base conversion, password generation, cron parsing, JSON formatting, timestamp conversion, Base64 and URL encoding, UUID and hash generation, storage unit conversion — without having to create an account, hit an arbitrary usage limit, or wonder where the data typed into a form actually goes.
Why it exists
Plenty of equivalent tools online are buried under intrusive ads, gate basic functionality behind sign-up, or quietly process input on a server without saying so. Toolbit was built with the opposite approach: every calculation runs in the visitor's own browser, the code stays simple enough to verify, and the site is funded through non-intrusive advertising rather than user data or subscriptions.
How it's built
The site is a Next.js app deployed on Render, statically generated, with no backend receiving what gets typed into a tool. Each calculator follows public, verifiable technical specifications — IP addressing RFCs, the standard entropy formula, the cron expression spec — rather than reinventing the logic from scratch.
The guides
Alongside the tools, the site publishes technical guides that dig into the topics the calculators solve in one click: how to work out a subnet by hand from the bits, how to solve a VLSM exercise, how to read and write cron expressions, how to handle timestamps and time zones, when to use UUID v4 or v7, which hash function fits which job, why a 1 TB drive shows 931 GB, and what password entropy actually measures. Every example is checked against the same code the tools run on, and each guide links to the matching tool with the values already filled in so the result can be verified.
What's next
The tool catalog keeps growing. If something useful is missing, or if anything on the site isn't working the way it should, the best way to say so is through the contact page.