The same maths, as an API

Everything this site computes is a verb on a shared adapter, reachable over HTTP and as an MCP tool, with its inputs and outputs declared.

Refusals come back as refusals

Asking the API for a lithium pack with no BMS returns refused true, the reasons, and no numbers at all. A caller cannot accidentally read an arrangement out of a design that was rejected, because there is not one in the response.

Every figure is an object, not a bare number

Each value comes back with its unit, a confidence of exact, derived or typical, and the basis it was computed from. That makes an answer checkable by whatever is consuming it, which matters more here than compactness.

Questions

Are these designs safe to build?

They are a design aid, not an engineering sign-off. Every result states the assumptions it used so you can check them, marks which figures rest on a typical value rather than a measurement, and always includes the protection the pack needs. Anything that will be charged unattended should be reviewed by somebody qualified.

Do I need a BMS?

For any lithium chemistry, yes, and this site will not design a pack without one. A BMS is the only thing that stops one cell being driven under-voltage on discharge or over-voltage on charge, and the divergence between cells is invisible from outside the pack. Lead-acid and NiMH can be built without one; lithium cannot.