# Effect Size Calculator API

> For the complete documentation index, see [llms.txt](/llms.txt).

Calculate Cohen's d, Hedges' g, Glass's delta, and related effect-size statistics for two groups.

Use this endpoint to add the tool to your app, site, workflow, or agent without rebuilding formulas, validation, examples, and docs.

- Slug: `effect-size-calculator`
- Category: `math`
- Version: `2026-04-22`
- Credits per successful call: 1
- Starts on: free
- Max payload: 65536 bytes
- Privacy mode: `hash_only`
- Available on: free, starter, pro, business, scale
- Browser tool: https://miniwebtool.com/effect-size-calculator/

## Endpoint

`POST https://api.miniwebtool.com/v1/tools/effect-size-calculator/run`

## Request body

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `mean1` | `float` | yes |  |
| `sd1` | `float` | yes |  |
| `n1` | `int` | yes |  |
| `mean2` | `float` | yes |  |
| `sd2` | `float` | yes |  |
| `n2` | `int` | yes |  |
| `precision` | `int` | no |  |

## Example request

```json
{
  "mean1": 85,
  "sd1": 10,
  "n1": 30,
  "mean2": 78,
  "sd2": 12,
  "n2": 30
}
```

## cURL

```bash
curl -X POST https://api.miniwebtool.com/v1/tools/effect-size-calculator/run \
  -H 'Authorization: Bearer mwt_live_YOUR_KEY' \
  -H 'Content-Type: application/json' \
  -d '{"mean1":85,"sd1":10,"n1":30,"mean2":78,"sd2":12,"n2":30}'
```

## Response envelope

```json
{
  "request_id": "01K...",
  "tool": "effect-size-calculator",
  "tool_version": "2026-04-22",
  "credits_used": 1,
  "result": {}
}
```

## Errors

Errors are RFC 7807 `application/problem+json`. Branch on `code`, not `title`.

## MCP

Agents can discover and call this tool through `https://api.miniwebtool.com/mcp` or `https://api.miniwebtool.com/v1/mcp` using MCP `tools/list` and `tools/call`.

## Frequently asked

### What does the Effect Size Calculator API do?

Calculate Cohen's d, Hedges' g, Glass's delta, and related effect-size statistics for two groups. Use it to add this utility without rebuilding formulas, validation, examples, and documentation.

### How much does one call cost?

1 credit per successful call. Failed calls do not bill.

### What parameters are required?

Required fields: mean1, sd1, n1, mean2, sd2, n2. Full schema at `https://api.miniwebtool.com/v1/openapi.json`.

### Is this deterministic?

Yes. Same input, same output. Tool version: 2026-04-22.