# Use American-style number formatting (EK00051)

import { Aside, Badge } from '@astrojs/starlight/components';

Using commas as thousands separators and a period as the decimal point keeps numeric values unambiguous and consistent across your documentation. EkLine flags numbers that don't follow American formatting conventions (rule EK00051).

## Why does number formatting matter in documentation?

Number formatting varies by region: some conventions use periods for thousands and commas for decimals, which reverses the American style. When a page mixes both, readers can misread `1.000` as one instead of one thousand. Most software and API documentation follows American formatting, and matching it keeps your numbers unambiguous and consistent with the tools your readers use.

## What EkLine flags

EK00051 matches numbers that use commas as the decimal point or periods as thousands separators and suggests the American form.

- ❌ **Incorrect:** The dataset contains 1.000.000 rows.
- ✅ **Correct:** The dataset contains 1,000,000 rows.
- ❌ **Incorrect:** Set the ratio to 3,5.
- ✅ **Correct:** Set the ratio to 3.5.

## How to fix

Use commas to separate thousands and a period for the decimal point.

<Aside type="note">
Version numbers, IP addresses, and other dotted identifiers aren't measurements. Review the suggestion in context before you apply it.
</Aside>

## FAQ

### How should you format large numbers?

Use commas to separate thousands and a period for the decimal point — 1,000,000 for a million and 3.5 for a ratio. This matches the format most software and API documentation uses.

### Does this rule apply to version numbers and IP addresses?

No. Version numbers, IP addresses, and other dotted identifiers aren't measurements. Review the suggestion in context before you apply it.

## Rule details

| Property | Value |
|----------|-------|
| Rule ID | `EK00051` |
| Category | Consistency |
| Default severity | <Badge text="Warning" variant="caution" /> |
| Enabled by default | Yes |

## Ignore this rule

To keep a number's formatting on one line, add an inline comment with a reason:

```markdown
<!-- ekline-ignore-next-line EK00051 -- locale-specific example -->
In this locale, one thousand is written 1.000.
```

To disable the rule across your project, add it to the `ignore` list in your [configuration file](/reviewer/configuration/ignoring-rules/#ignore).

## Related rules

- [EK00050](/reviewer/rules/ek00050/) — Abbreviate units of measurement
- [EK00008](/reviewer/rules/ek00008/) — Use the "January 01, 1970" date format