{
  "capability_id": "electrical.energy_cost",
  "tool_id": "energy-cost",
  "engine": "energy-cost",
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  "test_count": 28,
  "passed": 28,
  "failed": 0,
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  "reviewer_role": "electrical-engineer",
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    "Single flat unit rate"
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    "Usage cost only — standing charge and tax not included",
    "W, hours, days, kWh, and rate must be ≥ 0",
    "Hours per day must be ≤ 24 (HOURS_PER_DAY_OUT_OF_RANGE)",
    "Zero W/hours/days/kWh/rate → 0"
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    "Bad mode → INVALID_MODE; non-finite → INVALID_NUMBER",
    "Zero W / hours / days / kWh / rate → 0 cost — soft boundary",
    "mode=watts uses W×hours×days/1000×rate; mode=kwh uses kWh×rate"
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  "sources": [
    {
      "title": "NIST Guide to the SI (SP 811)",
      "section": "Kilowatt-hour as a common commercial unit of electrical energy",
      "url": "https://www.nist.gov/pml/special-publication-811",
      "supports": "Cost = kWh × rate; kWh = W × h × days / 1000",
      "kind": "reference"
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    {
      "title": "U.S. Energy Information Administration (EIA)",
      "section": "Electricity prices reported per kilowatt-hour",
      "url": "https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a",
      "supports": "Rate input ($/kWh) is user-supplied from local tariffs",
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      "tol": 0.01
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        "rate": 0.15
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