eve-fit-engine

A Pyfa-parity EVE Online ship & Upwell-structure fitting calculation engine, extracted from capsuleers.app. Given a fit and an SDE dataset, it returns the full derived stat block you'd see in a fitting tool: offense (DPS / alpha / application), defense (EHP / resists / tank), capacitor (stability / sim), navigation, targeting, fitting (CPU / PG / calibration), projected effects, and structure fuel/service stats.

Licence: GPL-3.0-or-later. This engine is a derivative work of pyfa-org/Pyfa and is distributed under the same terms. See NOTICE and LICENSE. The complete corresponding source is this repository.

Design

• Framework-free core. The base entry has no fetch, no fs, no window, no npm runtime deps. Runs in the browser, in Node, in a worker — anywhere.
• Two entries. Base (.): inject your own FittingDataset. Node (./node): batteries-included — bundles a snapshot of the EVE SDE (under CCP's licence, by mere aggregation) + an fs loader, so it works out of the box on the server.
• Validated against Pyfa two ways.
  • Fixture suite — npm run test:pyfa: 662 hand-curated assertions against Pyfa screenshots, All-V skills, zero tolerance overrides. This is the release gate and the engine's correctness ground truth.
  • Differential harness — npm run diff: generates 4 fits for every published ship and compares every stat against a headless pyfa-org/Pyfa oracle. 1662/1676 fits (99.2%) match exactly; the residual is a documented set of pyfa float/modelling/per-ship quirks (see test/diff/known-diffs.mjs). Exits 0 on no unexpected diffs; --strict re-lists the accepted set as failures.

Install

npm install eve-fit-engine

Usage — zero-config (Node, batteries-included)

The /node entry ships with the EVE SDE bundle (data/, ~8 MB) and a built-in loader. Give it an EFT string, get full stats — nothing else to set up:

import { computeFromEft } from 'eve-fit-engine/node'

const { fit, warnings, 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
`)

console.log(computed.derived.offense.totalDps)              // 197.6
console.log(computed.derived.defense.ehpTotalAgainstProfile)
console.log(computed.derived.navigation.maxVelocity)

Defaults to All-V skills; pass { skillProfile, damageProfile, targetProfile, … } as the second arg to override. loadBundledDataset() is also exported if you want the dataset directly.

The bundled SDE is CCP's, under CCP's EVE Online Developer License (see data/SDE-LICENSE.md) — included by mere aggregation, NOT under this package's GPL.

Usage — bring-your-own dataset (browser / custom / always-fresh SDE)

The base entry is environment-free (no fs, no bundled data). Inject a FittingDataset you build however you like:

import { computeFit, parseEft, type FittingDataset } from 'eve-fit-engine'

const dataset: FittingDataset = await buildYourDataset()   // your SDE bundle
const { fit } = parseEft(eftText, dataset)
const computed = computeFit(fit, dataset, { skillProfile /* … */ })

This is what capsuleers.app uses server-side: it builds its own always-fresh bundle and injects it, so it never depends on the (snapshot) bundled data.

What's NOT in this package

• 3D ship models, UI components — those live in the consuming application.
• The bundled SDE is a snapshot; for always-fresh data, inject your own via the base entry (see above).

Provenance / how parity is maintained

The engine mirrors Pyfa's eos calculation model: effect handlers keyed by EVE dogma effect IDs, stacking-penalty pools, a late-runtime resistance-adaptation pass, a discrete capacitor simulation (faithful port of eos/capSim.py — integer cycle times, turret-volley vs staggered drains, cap-booster injection), and spool-up handling. When CCP ships a new SDE, data-driven modifierInfo effects work automatically; new hardcoded mechanics in Pyfa's effects.py are tracked and ported, then re-checked against both the fixture suite (npm run test:pyfa) and the per-ship differential harness (npm run diff) before release. See MAINTENANCE.md for the update flows.

Contributing

See CONTRIBUTING.md — the step-by-step guide to setup, every internal command, the two validation suites (npm run test:pyfa + npm run diff), how to add fixtures / port effects, the pyfa-pin recalibration flow, and the project's hard rules.

Licence

GPL-3.0-or-later. Copyright (C) 2026 Capsuleers.app. This is free software; see LICENSE for details.