About FormatStack

What FormatStack is

FormatStack hosts six everyday developer tools — a JSON formatter and validator, a JSONPath tester, a regular expression tester, a UUID v4 generator, a Base64 encoder and decoder, and a cron expression parser. All of them are free, none of them require an account, and none of them ask you to sign up for anything.

Alongside the tools there is a growing set of reference guides — written to answer one specific question completely, tested against the runtimes they describe, and dated so you can see when they were last checked. They exist because the answer to "why does btoa throw on emoji" should not be forty identical blog posts that all stop before the part you needed.

Why it exists

Most online formatters and converters work by sending whatever you paste to a remote server, processing it there, and sending the result back. For a quick sanity check on a public snippet that is fine. For an API response containing customer records, an internal configuration file, or a token you are debugging, it is a genuine problem — you have just handed that data to a third party you know nothing about.

Every tool on this site is written in plain JavaScript that runs inside your browser tab. When you click "Format" on the JSON page, your browser's own JSON.parse does the work. The text in that textarea is never transmitted anywhere, which also means the tools keep working if your connection drops after the page loads.

How it is built

The whole site is static HTML, CSS, and vanilla JavaScript — no framework, no build step, no third-party libraries in the tools themselves. That is a deliberate choice: it keeps pages loading in well under a second, keeps the code small enough to audit by reading it, and means there is no dependency chain that can break or introduce unexpected behaviour.

Each tool uses native browser APIs rather than reimplementing them: JSON.parse and JSON.stringify for JSON, the built-in RegExp engine for regex, crypto.randomUUID() for identifiers, and TextEncoder with btoa for UTF-8-safe Base64. Results therefore match exactly what your own code will do.

Independent by design

FormatStack is an independent project, not affiliated with any company and not built to funnel you toward a paid product. There is no upsell, no "pro" tier, and no account to create. It exists because pasting internal data into services of unknown provenance is a habit worth breaking, and the tools that avoid it should be free.

That argument is made at length on the blog, alongside build notes on how the tools are put together. The guides are the reference half: evergreen, corrected in place, and dated so you can see how current they are.

How it is funded

The tools are free and are supported by advertising. Ads help cover the cost of the domain and hosting so the tools can stay free and account-free. Advertising and analytics providers do collect data about your visit, which is separate from the tool inputs described above — the specifics are laid out in the privacy policy.