# E=mc² Calculator API

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

Convert mass and energy using E=mc² with configurable conversion efficiency.

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

- Slug: `e-mc-calculator`
- Category: `science`
- 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/e-mc-calculator/

## Endpoint

`POST https://api.miniwebtool.com/v1/tools/e-mc-calculator/run`

## Request body

| Field | Type | Required | Description |
| --- | --- | --- | --- |
| `mode` | `str` | no | mass_to_energy | energy_to_mass Choices: mass_to_energy, energy_to_mass |
| `mass_value` | `float | None` | no |  |
| `mass_unit` | `str` | no | mg | g | kg | t | oz | lb Choices: mg, g, kg, t, oz, lb |
| `energy_value` | `float | None` | no |  |
| `energy_unit` | `str` | no | j | kj | mj | kwh | kcal | ton_tnt Choices: j, kj, mj, kwh, kcal, ton_tnt |
| `efficiency_preset` | `str` | no | complete | fusion | fission | custom Choices: complete, fusion, fission, custom |
| `custom_efficiency_percent` | `float | None` | no |  |
| `precision` | `int` | no |  |

## Example request

```json
{}
```

## cURL

```bash
curl -X POST https://api.miniwebtool.com/v1/tools/e-mc-calculator/run \
  -H 'Authorization: Bearer mwt_live_YOUR_KEY' \
  -H 'Content-Type: application/json' \
  -d '{}'
```

## Response envelope

```json
{
  "request_id": "01K...",
  "tool": "e-mc-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 E=mc² Calculator API do?

Convert mass and energy using E=mc² with configurable conversion efficiency. 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.