---
title: "ERC-2981 Royalty Calculator"
method: POST
path: "/v1/tools/calculate_erc2981_royalty"
tags: ["TODO_TAGS_REVIEW", "TODO_AP2_EXPORT_REVIEW"]
---

# ERC-2981 Royalty Calculator

`POST /v1/tools/calculate_erc2981_royalty`

## Request

- Base URL: `https://ainumbers.co`
- URL: `https://ainumbers.co/v1/tools/calculate_erc2981_royalty`
- Auth: none declared

Recomputes an ERC-2981 royalty amount as floor(sale_price * royalty_fraction_bps / 10000) -- the same integer-division convention the OpenZeppelin reference ERC2981 implementation uses -- from a caller-declared sale_price and royalty_fraction_bps, using BigInt arithmetic throughout so a sale_price beyond Number.MAX_SAFE_INTEGER never loses precision. Flags a bps value above 10000 (100%) as out of range (the value the reference implementation reverts on) while still reporting the raw recompute, and compares against an optional claimed_royalty_amount. Zero network calls: this tool never queries a contract's actual royaltyInfo() return value -- sale_price, royalty_fraction_bps, and receiver are all caller-declared. Cross-links 528-nft-metadata-validator and 521-cant-be-evil-nft-license-picker for adjacent NFT-standard surfaces (metadata shape, license terms) this tool does not cover. ERC-2981 royalty payment is a voluntary off-chain convention: this tool makes no claim that any marketplace will actually pay the computed amount.

**Tool URL:** https://ainumbers.co/chaingraph/art-608-erc2981-royalty-calculator.html

## Request body

- object
  - `claimed_royalty_amount` unknown, required
  - `receiver` string, required
  - `royalty_fraction_bps` unknown, required
  - `sale_price` unknown, required

## Response `200`

Successful tool execution result

- object
  - `claimed_royalty_amount` string
  - `computed_royalty_amount` string
  - `effective_royalty_pct` string
  - `findings` object[]
    - `check` string
    - `detail` string
    - `verdict` string
  - `not_proven` object[]
    - `detail` string
    - `item` string
  - `overall_determination` string
  - `receiver` string
  - `related_tools` object[]
    - `relation` string
    - `tool_id` string
  - `royalty_fraction_bps` string
  - `sale_price` string
  - `scope_note` string

---

[API](https://skmtc.dev/ainumbers/apis/ainumbers-co-fintech-intelligence-suite.md) · [All operations](https://skmtc.dev/ainumbers/apis/ainumbers-co-fintech-intelligence-suite/llms.txt) · [OpenAPI document](https://skmtc.dev/ainumbers/apis/ainumbers-co-fintech-intelligence-suite/revisions/b462e4f5bb28?raw)