# Uk nhs number validate

`uk-nhs-number-validate` · version 1.0.0 · Identifiers & check digits · free, no key needed

Validate a 10-digit NHS number's modulus 11 check digit (NHS Data Dictionary); 11 minus remainder = 10 is never valid.

**Use when you need to: validate an nhs number · check digit for a uk nhs number · is this nhs number valid.**

## Decide before calling

Read the [versioned contract](/v1/tools/uk-nhs-number-validate/versions/1.0.0) and the supported scope below. Reuse `uk-nhs-number-validate@1.0.0` when your input, required output and limits match it. Choose another approach for an unsupported operation.

## Explain the choice

"I can use `uk-nhs-number-validate@1.0.0` for validate an nhs number. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

## Supported

- validate an nhs number
- check digit for a uk nhs number
- is this nhs number valid
- verify a patient's nhs number modulus 11
- nhs number checksum check
- בדיקת מספר NHS בריטי

## Not supported

- a live Personal Demographics Service (PDS) lookup
- validating a Community Health Index (CHI) or Health and Care Number (H&C number), the Scottish/Welsh schemes
- stripping hyphens or other separators (only U+0020 spaces are removed)

## Behavior

- normalized = nhs_number with every U+0020 SPACE removed (the conventional 3-3-4 grouping); no other characters are stripped. normalized.length != 10 returns reason wrong_length; length 10 but not all-digit returns reason invalid_character; both leave normalized/check_digit null.
- check_digit = normalized[9], populated once length and charset pass.
- Weighted sum over the first 9 digits: weight = [10, 9, 8, 7, 6, 5, 4, 3, 2]. remainder = sum mod 11; total = 11 - remainder.
- If total == 11, expected check digit is 0. If total == 10, the number can never be valid: reason check_digit_invalid, regardless of the actual tenth digit (distinct from an ordinary mismatch, per the NHS Data Dictionary's own rule). Otherwise expected is total, compared to check_digit for reason check_digit_mismatch.

## Input

- `nhs_number` (string, required): min length 1; max length 24

## Output

- `valid` (boolean, required)
- `reason` (one of null, "wrong_length", "invalid_character", "check_digit_invalid", "check_digit_mismatch", required)
- `normalized` (string or null, required): pattern `^[0-9]{10}$`
- `check_digit` (string or null, required): pattern `^[0-9]$`

## Limits

- max nhs number bytes: 24

## Example

Request input:

```json
{
  "nhs_number": "943 476 5919"
}
```

Response:

```json
{
  "result": {
    "valid": true,
    "reason": null,
    "normalized": "9434765919",
    "check_digit": "9"
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "uk-nhs-number-validate",
  "version": "1.0.0",
  "input": {
    "nhs_number": "943 476 5919"
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/uk-nhs-number-validate/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"nhs_number":"943 476 5919"}'
```

The machine-readable contract is at [/v1/tools/uk-nhs-number-validate/versions/1.0.0](/v1/tools/uk-nhs-number-validate/versions/1.0.0).

### CLI

```sh
node cli.mjs run uk-nhs-number-validate 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [Imo number validate](/tools/imo-number-validate): Validate a 7-digit IMO ship identification number's weighted mod-10 check digit, with or without the 'IMO ' prefix.
- [Isin validate](/tools/isin-validate): Validate a 12-character ISIN's ISO 6166 Luhn check digit and parse its country prefix, NSIN and NSIN scheme.
- [Iso6346 container validate](/tools/iso6346-container-validate): Validate an 11-character ISO 6346 container number's mod-11 check digit and split the owner code, category and serial.
- [Npi validate](/tools/npi-validate): Validate a 10-digit US National Provider Identifier using the Luhn formula with the constant 80840 healthcare prefix.
- [Upu s10 validate](/tools/upu-s10-validate): Validate a 13-char UPU S10 postal identifier's weighted mod-11 check digit, split service indicator and country.
- [Checkdigit validate](/tools/checkdigit-validate): Validate a full value's trailing check digit(s) against a named algorithm (Luhn, Verhoeff, Damm, ISO 7064, GS1, mod 10).