> For the complete documentation index, see [llms.txt](https://docs.internetobject.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.internetobject.org/schema-definition-language/data-types/decimal.md).

# Decimal

The **`decimal`** type validates an exact, fixed-precision decimal — for money and other values where binary floating point would lose accuracy. In data it is written with an `m` suffix: `123.45m`.

> For the literal syntax, see [Decimal values](/structure-and-syntax/values/number/decimal.md).

## TypeDef

A `decimal` MemberDef accepts only the options below. Any other key is invalid.

| Option       | Type             | Description                                                     |
| ------------ | ---------------- | --------------------------------------------------------------- |
| `type`       | string           | The type name `decimal`. First positional value.                |
| `default`    | decimal          | Value used when the member is omitted. Second positional value. |
| `choices`    | array of decimal | Restricts the value to a fixed set.                             |
| `precision`  | int              | Maximum total number of significant digits.                     |
| `scale`      | int              | Exact number of digits after the decimal point.                 |
| `min`        | decimal          | Minimum allowed value (inclusive).                              |
| `max`        | decimal          | Maximum allowed value (inclusive).                              |
| `multipleOf` | decimal          | The value must be an exact multiple of this.                    |
| `optional`   | bool             | If `true`, the member may be omitted. Shorthand: `?` suffix.    |
| `null`       | bool             | If `true`, the member may be `null`. Shorthand: `*` suffix.     |

### No format option

Unlike the other numeric types, `decimal` has **no `format` option** — and this is deliberate, not an omission. A `format` selects among the literals that can express a value, and a decimal has only one: `<digits>.<digits>m`. Radix notations cannot express a fractional value, and [scientific notation is not part of the decimal literal](/structure-and-syntax/values/number/decimal.md) (`1.23e2m` is invalid). With a single possible spelling there is nothing to select.

The `m` suffix is always written; without it the output would read back as a plain number.

## Precision & scale

`precision` and `scale` together give SQL-style `DECIMAL(precision, scale)` validation:

* **scale** — the number of fractional digits MUST equal `scale`.
* **precision** — the total significant digits MUST NOT exceed `precision`.

```ruby
price: { decimal, precision: 5, scale: 2 }
---
~ 123.45m    # ✓  (5 digits, 2 after the point)
```

```ruby
rate: { decimal, scale: 2 }
---
~ 1.5m       # ✗ invalid-scale  (1 fractional digit, scale requires 2)
```

> With neither `precision` nor `scale`, a `decimal` is compared by its exact value.

## Optional, nullable & defaults

Resolution follows the [common rules](/schema-definition-language/data-types/number.md#optional-nullable--defaults):

```ruby
amount?*: decimal
---
~ {}      # ✓ omitted → absent
~ N       # ✓ null
~ 9.99m   # ✓
```

## See Also

* [Decimal values](/structure-and-syntax/values/number/decimal.md)
* [Numeric Types](/schema-definition-language/data-types/number.md) · [BigInt](/schema-definition-language/data-types/bigint.md)
* [TypeDef](/schema-definition-language/advanced-schema-concepts/typedef.md) · [MemberDef](/schema-definition-language/advanced-schema-concepts/memberdef.md)


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