Design import
The rocket's structure arrives as real components with real parameters, versioned like anything else in the product. A change in the design file becomes a change you can see and review, rather than one that quietly invalidates a number three documents downstream. Every flavour of the file format is read directly, compressed or not, and every value in it is already in SI units, so nothing is converted on the way in and there is no unit to get wrong.
3D view
The imported airframe renders in 3D with true wall thickness and a contrast mode for reviewing geometry. That is more useful than it sounds in the review meeting where somebody has to actually look at the thing being described, and it is the fastest way to catch the class of mistake that survives every numerical check because it only looks wrong.
Motor curves and a vertical flight check
Motor thrust curves come in from the standard motor file format, and a built-in vertical flight simulation answers whether a given motor gets this airframe to roughly the altitude you need. It integrates thrust, gravity and drag against a standard atmosphere, and reports the numbers a launch actually turns on: apogee, the speed leaving the rod, and descent under the parachute. It is deliberately a simpler model than a full six-degree-of-freedom run, no wind and no stability, so it is a check against the design rather than a replacement for the design tool. Simulations already stored in the imported file are read out and shown alongside it.
Running your own Python model
A team that has written its own model can run it here. Member-authored Python runs against the imported design in the browser, on a full Python runtime compiled to run in the tab, given the same inputs the built-in check uses and returning its own summary numbers and plotted series. The script never reaches our servers: it executes in the member's own browser with no more privilege than the page already has. Most serious teams have a descent model or a recovery calculation somebody wrote in a course, and it usually lives in a notebook on one laptop, which is the same disappearing act every other number used to do.