# Digital Root Calculator API

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

Repeated digit sum or product to a single digit in base 2, 8, 10, or 16, with persistence and the casting-out-nines formula check.

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

- Slug: `digital-root-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/digital-root-calculator/

## Endpoint

`POST https://api.miniwebtool.com/v1/tools/digital-root-calculator/run`

## Request body

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `number` | `str` | yes | Non-negative integer in the chosen base |
| `mode` | `str` | no | additive | multiplicative Choices: additive, multiplicative |
| `base` | `str` | no | 10 | 2 | 8 | 16 Choices: 10, 2, 8, 16 |

## Example request

```json
{
  "number": "987654321",
  "mode": "additive",
  "base": "10"
}
```

## cURL

```bash
curl -X POST https://api.miniwebtool.com/v1/tools/digital-root-calculator/run \
  -H 'Authorization: Bearer mwt_live_YOUR_KEY' \
  -H 'Content-Type: application/json' \
  -d '{"number":"987654321","mode":"additive","base":"10"}'
```

## Response envelope

```json
{
  "request_id": "01K...",
  "tool": "digital-root-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 Digital Root Calculator API do?

Repeated digit sum or product to a single digit in base 2, 8, 10, or 16, with persistence and the casting-out-nines formula check. 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: number. Full schema at `https://api.miniwebtool.com/v1/openapi.json`.

### Is this deterministic?

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