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eve-fit-engine

eve-fit-engine is an npm package that computes the derived stat block of an EVE Online ship or Upwell structure fit: offense (DPS, alpha, application), defense (EHP, resists, active and passive tank), capacitor (stability and simulation), navigation, targeting, fitting (CPU / powergrid / calibration), projected effects, and structure fuel and service stats.

It is the calculation engine behind Capsuleers.app, extracted so that other developers can build fitting tools without reimplementing dogma.

Two entry points

  • Base (eve-fit-engine) — framework-free. No fetch, no fs, no window, no npm runtime dependencies. You inject your own FittingDataset, so it runs in the browser, in Node, or in a worker, against whichever SDE snapshot you keep.
  • Node (eve-fit-engine/node) — batteries included. Ships a version-pinned snapshot of the EVE Static Data Export plus a loader, so an EFT string in gives full stats out with nothing else to set up.
import { computeFromEft } from 'eve-fit-engine/node'

const { computed } = await computeFromEft(`
[Rifter, My Fit]
200mm AutoCannon II, Republic Fleet EMP S
200mm AutoCannon II, Republic Fleet EMP S
1MN Afterburner II
Gyrostabilizer II
`)

computed.derived.offense.totalDps
computed.derived.defense.ehpTotalAgainstProfile
computed.derived.navigation.maxVelocity

Skills default to all-V; pass a skillProfile, damageProfile or targetProfile to override.

Correctness

The engine is validated against Pyfa two ways, because a fitting engine that is nearly right is a fitting engine nobody can trust:

  • Fixture suite — 662 hand-curated assertions against Pyfa, all-V skills, zero tolerance. This is the release gate.
  • Differential harness — generates four fits for every published ship and compares every stat against a headless Pyfa oracle. 1662 of 1676 fits (99.2%) match exactly; the residual is a documented set of Pyfa float and per-ship modelling quirks, listed in the repository rather than hidden.

Licensing

The engine is GPL-3.0-or-later: it is a derivative work of Pyfa, whose calculation semantics it mirrors, and it is distributed under the same terms. The complete corresponding source is the linked repository.

The bundled SDE snapshot is included by mere aggregation and is not covered by the GPL — it remains governed by the EVE Online Developer License Agreement. See NOTICE and data/SDE-LICENSE.md in the repository.