A few months ago I wanted to do something trivial: format an ugly blob of JSON. I googled "json formatter", clicked the first result, and was met with a cookie wall, three ad reloads, and a little banner asking me to create an account. To format JSON. In my own browser.
That was the moment 123MiniApps started. The idea was simple and a little stubborn: small tools should be fast, free, and private, and they should not ask you for anything. No sign-up, no upload, no "continue with Google". You open the page, you use the tool, you leave.
It is now a collection of 116 of these tools, and I want to share how it is built and a few things I learned making it.
The one rule: nothing leaves your device
Every tool runs 100% client-side. The JSON you paste, the image you drop in, the text you type - it is all processed by JavaScript in your own browser. There is no backend to send it to. That is not a marketing line, it is the architecture: the site is static, and there simply is no server endpoint that receives your data.
This matters more than it sounds. People paste real things into these tools: API responses with tokens, config files, half-finished writing, personal photos. On most "online tool" sites, that data is uploaded to someone's server to be processed. Here you can open your browser's Network tab, use a tool, and watch: no request carries your file. You can verify the privacy claim yourself, which is the only kind of privacy claim worth making.
What is actually in it
116 tools across 11 categories - text, image, developer, converters, generators, calculators, security, design, content, productivity, and fun. A few that get the most use:
A JSON formatter that shows the exact line and column of an error instead of just "invalid".
A password generator using the browser's crypto API, so the randomness is real and never transmitted.
An image compressor that shrinks photos entirely on your device.
There are also converters, QR makers, color and contrast tools, unit and timestamp converters, and a pile of small text utilities.
Three things I learned building it
"Boring" client-side tools are surprisingly capable. Things I assumed needed a server usually did not. Image compression and conversion? The Canvas API. Hashing and secure random values? The Web Crypto API. Even generating a PDF from images can be done in pure JavaScript by writing the PDF bytes directly - no library, no upload. Once you commit to "the browser is the computer", a lot of features fall out for free, and the privacy story writes itself.
One tool, one page, one job. Every tool is its own focused page rather than a mega-app with tabs. It loads faster, it is easier to link to and bookmark, it is easier for search engines to understand, and it is calmer to use. Constraints made the product better.
Consistency beats cleverness. I ended up generating the pages from a small set of Python build scripts and a shared toolkit, so all 116 tools share the same layout, the same accessible components, and the same structured data. Adding tool 117 is now mostly writing its logic, not its chrome. If you are building many similar pages, invest early in the generator - it pays for itself fast.
What is next
I am adding tools and writing plain-language guides on the blog explaining the concepts behind them (why your JSON is invalid, how bionic reading works, what BMR actually measures, and so on). The goal is not to be the biggest tool site, just the one you can trust with a quick job and not feel watched.
If you want to poke at it, it is here: https://www.123miniapps.online - and I would genuinely like to know which tools you reach for and what is missing. I read every reply.
Thanks for reading.
