Who runs this

Why it exists

I design telescopes in Fusion 360 and print them. That means a steady traffic of STEP, STL and 3MF files between CAD, slicers and machine shops, and a steady supply of the questions this site answers: what a format actually stores, why a part came in 25.4 times too small, and what a conversion silently threw away. The free converters I found either uploaded the file to a server they said nothing about, or reported success without saying what was lost. This site is the tool I wanted.

What is checked, and how

The site's claims are generated from evidence rather than written by hand, and the rules are enforced in code, not in a style guide.

• A conversion gets a page only after it passes a test. Every one of the 120 pair pages is generated from a run against a public test corpus. A pair that fails gets no page. The corpus is CC0 and every file in it carries its provenance.
• Every fact carries its source and the date it was checked. The capability table on each format page links to the standard, the vendor's documentation or the maintainer's source, and shows when it was read. Where a source could not confirm something, the row says "unconfirmed" rather than guessing.
• Nothing is uploaded. 105 of the 120 conversions and every viewer run in your browser as WebAssembly. The 15 conversions that rebuild a solid from a mesh run on a server: the page says so before you choose a file, the file is deleted within an hour, and no record is kept that could identify you. The privacy page describes exactly what that server sees, and a test reads the database schema to make sure it cannot hold an IP address, a filename or an account.
• Every component we ship is listed. The licences page names each library, its licence, the exact artefact served and its hash, so the build can be reproduced. This build: occt 0.0.23, three 0.185.1, rhino3dm 8.32.2, built 2026-09-04.

What it does not do

It does not read DWG, DXF, SolidWorks or Parasolid files, because there is no way to do that in a browser under a licence that can be listed honestly. It does not repair meshes or edit geometry. It does not rebuild exact curves from triangles: the STL to STEP conversion produces planar faces and says so, in the caveat above the button. If a page says a format is read-only, that is a limit of the open-source kernel, not a paywall.

Corrections

If a fact on a format page is wrong, or a conversion did something its page does not describe, write to jeff@hooton.codes with the page and, if you can share it, the file. Corrections are made to the source table, with the new source and date, so the fix shows on the page with its evidence.