# magent BRI Calculator

> magent BRI Calculator is a paid API for AI agents from api.magentlab.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-13).

Computes Body Roundness Index (BRI) from height and waist circumference using the Thomas 2013 ellipse formula

## Facts

- Endpoint: GET https://api.magentlab.com/api/calc/bri
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-13
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/magent-bri-calculator-2d51ec9e
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_pHCPjiVSgoIE26bOUeI7C

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability magent-bri-calculator-2d51ec9e
```

Example prompt: Calculate the Body Roundness Index for someone who is 175 cm tall with a waist circumference of 90 cm using the Thomas 2013 formula.

## When to prefer this

Use this endpoint when you need a fast, reproducible, citation-backed BRI calculation (Thomas 2013) without building the formula yourself. Prefer it over body-fat or VAT estimation endpoints — this is purely an anthropometric index, not a diagnostic or body composition tool. Best suited for health apps, clinical research pipelines, and population screening workflows that need a standard BRI score from height and waist inputs.

## Known failure modes

- Missing waist_cm parameter returns a validation error
- waist_cm outside plausible range (40–200 cm) may be rejected or produce out-of-range BRI
- Neither height_cm nor height_in provided results in a missing-parameter error
- Non-numeric inputs cause schema validation failure
- Payment failure (402) if x402 USDC payment header is not included

## How this service works

Body roundness index from height and waist (Thomas 2013). Models the body as an ellipse: e = sqrt(1 - (waist/(pi*height))^2), BRI = 364.2 - 365.5*e. Deterministic published formula with citation. Not a medical device, VAT measurement, or body-fat diagnosis; magent does not measure the patient.

## Output

Returns a numeric Body Roundness Index (BRI) value computed from the Thomas 2013 formula: BRI = 364.2 - 365.5 * sqrt(1 - (waist/(pi*height))^2), where both measurements are normalized to the same unit. The response is a deterministic, reproducible score reflecting how 'round' the body shape is relative to a circle.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "headers": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    },
    "queryParams": {
     "type": "object",
     "required": [
      "waist_cm"
     ],
     "properties": {
      "waist_cm": {
       "type": "number",
       "description": "Waist circumference in centimeters (40-200). Compared to height in cm after normalize."
      },
      "height_cm": {
       "type": "number",
       "description": "Height in centimeters. Provide height_cm or height_in."
      },
      "height_in": {
       "type": "number",
       "description": "Height in inches. Converted as cm = in * 2.54."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/magent-bri-calculator-2d51ec9e/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.magentlab.com](https://www.zero.xyz/host/api.magentlab.com/llms.txt)