# A/B Test Sample Size Calculator API

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

Size an A/B test from baseline rate, minimum detectable effect, significance, and power.

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

- Slug: `a-b-test-sample-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/a-b-test-sample-size-calculator/

## Endpoint

`POST https://api.miniwebtool.com/v1/tools/a-b-test-sample-size-calculator/run`

## Request body

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `baseline_rate_pct` | `float` | no | current conversion rate in percent |
| `mde_value` | `float` | no | minimum detectable effect |
| `mde_mode` | `str` | no | relative | absolute Choices: relative, absolute |
| `alpha_pct` | `str` | no | 5 | 1 | 10 Choices: 5, 1, 10 |
| `power_pct` | `str` | no | 80 | 85 | 90 | 95 Choices: 80, 85, 90, 95 |
| `test_type` | `str` | no | two_tailed | one_tailed Choices: two_tailed, one_tailed |
| `num_variants` | `int` | no | total arms including control |
| `daily_visitors` | `float` | no | optional traffic per day for a duration estimate |
| `allocation_pct` | `float` | no | share of traffic entering the test |

## Example request

```json
{
  "baseline_rate_pct": 5,
  "mde_value": 10,
  "mde_mode": "relative",
  "alpha_pct": "5",
  "power_pct": "80",
  "test_type": "two_tailed",
  "num_variants": 2,
  "daily_visitors": 2000,
  "allocation_pct": 100
}
```

## cURL

```bash
curl -X POST https://api.miniwebtool.com/v1/tools/a-b-test-sample-size-calculator/run \
  -H 'Authorization: Bearer mwt_live_YOUR_KEY' \
  -H 'Content-Type: application/json' \
  -d '{"baseline_rate_pct":5,"mde_value":10,"mde_mode":"relative","alpha_pct":"5","power_pct":"80","test_type":"two_tailed","num_variants":2,"daily_visitors":2000,"allocation_pct":100}'
```

## Response envelope

```json
{
  "request_id": "01K...",
  "tool": "a-b-test-sample-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 A/B Test Sample Size Calculator API do?

Size an A/B test from baseline rate, minimum detectable effect, significance, and power. 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: (none). Full schema at `https://api.miniwebtool.com/v1/openapi.json`.

### Is this deterministic?

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