Amazon Fulfillment Fee Change Margin Audit

Reconcile two authorized fulfillment fee-schedule exports against your own SKU costs and dimensions. The Actor flags SKUs whose fulfillment fee or projected contribution margin changed, and it refuses to run when a fee input is missing.

It works only on data you paste in. It does not scrape Amazon, call any Amazon API, or make any network request.

What it does

• Matches SKUs across an earlier fee export, a later fee export and your product list.
• Computes contribution margin per unit before and after: price - referral fee - fulfillment fee - other cost - unit cost.
• Flags fee increases/decreases, margin drops, margins below your floor, negative margins, size-tier changes, and mismatches between your dimensions/weight and the fee export (orientation-insensitive).
• Estimates monthly profit impact when you provide monthlyUnits, and the price that would restore your minimum margin at the new fee.
• Writes a run SUMMARY record (key-value store) with counts, coverage, unmatched fee rows and caveats.

Fail-closed behavior

• The run is refused (no results, no charges) if oldFeeSchedule, newFeeSchedule or products is empty or malformed.
• A product with no fee in either export gets status missing_fee_input and no margin numbers. Conflicting duplicate fee rows, non-numeric fees, invalid product values and duplicate products are also reported with their own status and are never billed.

Sample input

{
  "oldFeeSchedule": [
    {"sku": "MUG-BLUE-12", "fulfillmentFee": 3.22, "sizeTier": "Standard", "lengthIn": 5, "widthIn": 4, "heightIn": 4, "weightLb": 0.9},
    {"sku": "YOGA-MAT-6", "fulfillmentFee": 5.40, "sizeTier": "Standard", "lengthIn": 24, "widthIn": 6, "heightIn": 6, "weightLb": 2.4}
  ],
  "newFeeSchedule": [
    {"sku": "MUG-BLUE-12", "fulfillmentFee": 3.40, "sizeTier": "Standard", "lengthIn": 5, "widthIn": 4, "heightIn": 4, "weightLb": 0.9},
    {"sku": "YOGA-MAT-6", "fulfillmentFee": 6.25, "sizeTier": "Large", "lengthIn": 26, "widthIn": 7, "heightIn": 7, "weightLb": 2.4}
  ],
  "products": [
    {"sku": "MUG-BLUE-12", "price": 18.99, "unitCost": 4.10, "monthlyUnits": 300, "lengthIn": 5, "widthIn": 4, "heightIn": 4, "weightLb": 0.9},
    {"sku": "YOGA-MAT-6", "price": 24.99, "unitCost": 8.50, "otherCostPerUnit": 0.60, "monthlyUnits": 120, "lengthIn": 24, "widthIn": 6, "heightIn": 6, "weightLb": 2.4}
  ],
  "defaultReferralFeeRatePct": 15,
  "minContributionMarginPct": 15
}

Input fields

Field	Notes
oldFeeSchedule, newFeeSchedule	Required. Rows with sku, fulfillmentFee; optional sizeTier, lengthIn, widthIn, heightIn, weightLb.
products	Required. sku, price, unitCost; optional referralFeeRatePct, otherCostPerUnit, monthlyUnits, dimensions, weight.
defaultReferralFeeRatePct	Your assumption when a product has no rate (default 15).
feeChangeThresholdPct, marginDropThresholdPoints, minContributionMarginPct, dimensionTolerancePct	Flag thresholds.
onlyFlagged	Return only flagged SKUs (unaudited rows are always returned).
maxSkus	Cap on products per run (default 5000).

Numbers may be given as numbers or strings such as "$1,234.50". SKU matching ignores case and surrounding spaces.

Output

One dataset row per product: sku, status, severity (none, low, medium, high, critical), flags, old/new fee, fee change and percent, old/new margin and margin percent, marginChangePoints, monthlyProfitImpact, priceForMinMargin, and reason for rows that could not be audited.

Pricing event

The code emits one sku-audited event per successfully audited SKU delivered. Rows with any error status are never charged, and the run stops if the user's maximum charge limit is reached. No payable plan is configured in this repository.

Limitations and caveats

• Results are only as accurate as the exports and costs you supply; nothing is verified against Amazon.
• Referral fees are an assumed percentage, not looked up. Returns, storage, inbound, advertising and taxes are not modeled.
• Fee matching is per SKU; it does not recompute fee tiers from dimensions, so it cannot tell you what Amazon should charge.
• Monthly impact assumes constant volume. With fewer than 30 audited SKUs, averages and totals are anecdotal, not statistically meaningful.
• The Actor does not judge whether a flagged change is an error or a legitimate rate change; it only surfaces it for review.
• Only use fee exports you are authorized to access.