> ## Documentation Index
> Fetch the complete documentation index at: https://persian-tools.usestrict.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Legal ID

> Validate Iranian Legal IDs (شناسه ملی حقوقی) — 11-digit company identifiers with a check digit.

The Iranian Legal ID (شناسه ملی حقوقی) is an 11-digit identifier for companies and legal entities, with its own check-digit algorithm distinct from the personal National ID.

## Function

```ts theme={null}
verifyIranianLegalId(legalId: string | number): boolean | undefined
```

```ts theme={null}
import { verifyIranianLegalId } from "@persian-tools/persian-tools";

verifyIranianLegalId("10380284790"); // true
verifyIranianLegalId(10380284790); // true (number accepted)
verifyIranianLegalId("00000000000"); // false (all zeros)
verifyIranianLegalId(undefined as any); // undefined
```

## Algorithm

1. Falsy input → `undefined`.
2. Stringify; length must be ≥ 11.
3. Reject if `parseInt(legalId) === 0`.
4. Reject if the middle 6 digits (`slice(3, 9)`) are all zero.
5. Compute check digit with coefficient vector `[29, 27, 23, 19, 17]` (cycled per period of 5):
   ```
   d   = digit[9] + 2
   sum = Σ (d + digit[i]) * z[i mod 5]  for i in 0..9
   sum = sum mod 11
   if sum === 10, sum = 0
   valid = digit[10] === sum
   ```

## Pitfalls

* **Length check is `< 11`, not `=== 11`.** Inputs longer than 11 chars are accepted; the algorithm slices fixed indices, so longer strings can still validate. If you need strict 11-digit input, check `String(input).length === 11` separately.
* **Persian/Arabic digit input is not normalized.** `parseInt("۱۰۳۸۰۲۸۴۷۹۰")` is `NaN`. Run `autoConvertDigitsToEN` first.
* **Return type is `boolean | undefined`** — use `=== true`, not truthy.
* **For personal IDs** (10 digits, different algorithm), use `verifyIranianNationalId`.

## Source

`src/modules/legalId/index.ts` · Tests: `test/verifyIranianLegalId.spec.ts`