Introduction
Fitness Tools is a set of deterministic fitness calculators — TDEE, body fat, one-rep max, macros, activity multiplier, powerlifting attempts, muscular potential, FFMI, and RSMI.
Why it exists
Section titled “Why it exists”Most fitness calculators give you one number from one formula and hide the math. But experts don’t agree on a single formula — there are several published equations for most of these metrics, and they disagree. Fitness Tools runs all the applicable published formulas and reports a consensus (mean, median, and the min–max range) across them. You get a defensible range and can see every method that produced it, instead of trusting one black box.
Two more things follow from that stance:
- Validated input. Every tool carries a Zod schema, so bad input (a negative age, an impossible body-fat) is caught at the boundary with structured, per-field errors — the same schema also generates the API docs.
- Runs anywhere. The library is isomorphic — no Node-only APIs — so the identical code runs in a browser, an edge function, or a server, with one small dependency.
One core, three protocols
Section titled “One core, three protocols”The calculators live in one library; everything else is the same math behind a different transport:
@almostjacked/fitness-tools— the npm library. The product. Install, import, call.@almostjacked/fitness-tools-api— a reference HTTP server over the library, for non-JS or remote callers.@almostjacked/fitness-tools-mcp— an MCP server over the library, for agents and LLM clients.
Same inputs, same outputs, same consensus — the only difference is how you call it.
Where to next
Section titled “Where to next”- New here? Get started — install and run your first calculation, then plan a cut end-to-end.
- Browse what each calculator does in Tools.
- Understand the design in Concepts.