# Check Digits (remote · check-digits.toolstop.dev)

Catch a mistyped barcode, ISBN, VIN, NPI or LEI before a bad identifier corrupts a record.

- Trust score: 58/100 (low)
- Registry status: active
- Liveness: live
- Owner verified: no
- Last scored: 2026-08-13

## Components

- remote · `check-digits.toolstop.dev`: 58/100 (this document), [markdown](https://verifymcp.io/servers/dev-toolstop-check-digits/check-digits.md), [page](https://verifymcp.io/servers/dev-toolstop-check-digits/check-digits)
- npm · `@toolstop/check-digits`: 78/100, [markdown](https://verifymcp.io/servers/dev-toolstop-check-digits/toolstop-check-digits.md), [page](https://verifymcp.io/servers/dev-toolstop-check-digits/toolstop-check-digits)

## Channel facts

- Endpoint: `https://check-digits.toolstop.dev`
- Transports: `streamable-http`
- Auth: `none`
- Version: `0.2.2`

## Trust breakdown

How this component scores in each security and reliability category. Every signal is checked automatically against the live server, and we only credit what we can confirm. Scores are 0–100 per category. Scoring method: https://verifymcp.io/docs/scoring (what has changed: https://verifymcp.io/docs/scoring/changelog)

Scored 2026-08-13.

- **Endpoint Security**: 46/100
  - The endpoint's TLS certificate is valid, in date, and uses a strong key.
  - Authorisation not fully verified: no authorisation is required to call this server, and 3 tool(s) never declared a destructiveHint. The MCP spec treats an absent hint as destructive by default, so we cannot call this surface safe.
  - HTTPS check failed: the endpoint is reachable over plaintext HTTP.
  - HSTS check failed: the Strict-Transport-Security header is absent.
  - DNSSEC check failed: this domain isn't protected by DNSSEC.
- **Transport & Reachability**: 100/100
  - Verified streamable-http transport via a live MCP handshake.
- **Schema Quality & AI Usability**: 66/100
  - AI-judged instruction clarity (excellent).
  - Context-footprint check failed: tool/resource definitions use about 920 tokens (~306/item across 3 items; 3 tools + 0 resources), over budget; trim descriptions and params.
  - Usage-examples check failed: none of the tools include examples.
- **Stability & Change Management**: 20/100
  - Stability observed for 6 of 30 days with no destabilising changes; credit accrues until the full window elapses.
- **Tool Coverage**: 100/100
  - 100% of tools have a non-trivial description (not blank, and not just the tool's name).
  - 100% of tool parameters carry a description.
  - Structured output schemas are declared (100% of tools); any adoption earns full credit.
- **Capabilities**: 60/100
  - Spec-recency check failed: implements MCP spec 2025-06-18; the latest is 2026-07-28.

## Install

### Claude

```bash
claude mcp add --transport http dev-toolstop-check-digits https://check-digits.toolstop.dev/
```

### Codex

```toml
[mcp_servers.dev-toolstop-check-digits]
url = "https://check-digits.toolstop.dev/"
```

### opencode

```json
{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "dev-toolstop-check-digits": {
      "type": "remote",
      "url": "https://check-digits.toolstop.dev/",
      "enabled": true
    }
  }
}
```

### OpenClaw

```bash
openclaw mcp add dev-toolstop-check-digits --url https://check-digits.toolstop.dev/ --transport streamable-http
```

### Hermes

```yaml
mcp_servers:
  dev-toolstop-check-digits:
    url: "https://check-digits.toolstop.dev/"
```

### Other

```json
{
  "mcpServers": {
    "dev-toolstop-check-digits": {
      "type": "http",
      "url": "https://check-digits.toolstop.dev/"
    }
  }
}
```

The mcpServers block is a cross-client convention. Remote transports vary, so check your client's docs.

## Changelog

Every change recorded for this component, newest first. Days that predate change tracking, or that we cannot explain, say so: "we were watching and nothing happened" and "we were not watching" are different claims.

### 2026-08-13 (score 58, +1)

No change was recorded against any check on this day. Stability & Change Management went from 17 to 20. That category is still filling its 30-day observation window: 5 days of observed history at the previous scan, 6 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-08-11 (score 57, +1)

- [security regression] HTTPS: unverified → fail
- [security] The server rewrote its instructions, which are the text every model session reads
- [functional] We updated how we score, so this day's move reflects our rubric, not a change to the server
- [functional] Server version: 0.2.0 → 0.2.2

### 2026-08-10 (score 56, +1)

No change was recorded against any check on this day. Stability & Change Management went from 7 to 10. That category is still filling its 30-day observation window: 2 days of observed history at the previous scan, 3 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-08-08 (score 55, +1)

- [functional improvement] Stability: unverified → 0.03

### 2026-08-07 (score 54)

First indexed and scored.

## MCP tools (3)

### `validate_identifier` (~246 tokens)

Check whether an identifier is mistyped

Verify a number when you already know what it is supposed to be. Use this whenever someone gives you a product barcode (GTIN, UPC or EAN), a book number (ISBN-10 or ISBN-13), a vehicle VIN, a US healthcare provider NPI, a security ISIN, or a legal entity LEI, and acting on a wrong one would cost something: a bounced claim, a rejected listing, a record that quietly corrupts a dataset.

Every supported format is a public identifier. Bank accounts, IBANs, routing numbers and payment cards are not supported and must not be sent.

Returns whether the checksum passes and, when it fails, the specific reason. If you do not already know the format, call identify_format first rather than guessing a `kind`, since a valid identifier checked against the wrong format comes back invalid. A passing checksum proves only that the digits are internally consistent: it does not mean the book, product, vehicle or provider exists, is active, or belongs to any particular person.

Input parameters:

- `kind` (string, required): Which identifier format to validate against.
- `value` (string, required): The identifier to check. Spaces and dashes are ignored.

Output parameters:

- `actualCheckDigit` (string): The digit the VIN actually carries at position 9. VIN only.
- `code` (string): Bounded reason the check failed. Absent when valid.
- `country` (string): ISO country code parsed from the identifier. ISIN only.
- `expectedCheckDigit` (string): The digit a VIN should carry at position 9. VIN only.
- `normalized` (string): The input with spaces and dashes removed, upper-cased.
- `reason` (string): Human-readable detail on the failure. Absent when valid.
- `valid` (boolean): Whether the check digit is arithmetically consistent.
- `width` (string): The resolved width of a GTIN. GTIN input only.

### `identify_format` (~169 tokens)

Work out what an unlabeled number is

Identify a bare number whose type was never recorded. Tests it against every supported format and reports which ones its check digit satisfies. Use it for an unlabeled spreadsheet column, a value pulled out of a log line or a scanned document, or any number handed over without being named.

Reports every format that matches rather than choosing between them. Several matches is normal and does not mean the answer is unclear: some formats are subsets of others, so every ISBN-13 is also a valid EAN-13, and a short value can satisfy two unrelated formats by chance. Read one match as strong evidence and several as a set to narrow from context. As with validation, a match means the arithmetic is consistent, not that the identifier is registered or real.

Input parameters:

- `value` (string, required): The identifier to classify.

Output parameters:

- `input` (string): The normalized input that was tested.
- `matched` (boolean): Whether any supported format matched.
- `matches` (array): Every format whose check digit the input satisfies, in registry order. Each entry carries `kind` plus the same format-specific fields validate_identifier returns for that format, such as `country` fo…

### `compute_luhn_digit` (~169 tokens)

Complete a number that is missing its check digit

Given digits with the final check digit omitted, return the one that completes them. US healthcare NPIs and securities ISINs use the Luhn formula.

Use it to build valid test fixtures, to recover a last digit that was lost or illegible, or to check an implementation against a reference. To test a number you already have in full, use validate_identifier instead. Input must reduce to digits only once spaces and dashes are stripped; anything else is an error. Payment cards also use Luhn, and are deliberately out of scope here: do not pass card digits, partial or complete. This constructs a well-formed number and nothing more: it does not create, reserve or verify a real provider or security.

Input parameters:

- `partial` (string, required): Digits excluding the final check digit.

Output parameters:

- `checkDigit` (string): The single digit that completes a Luhn-valid string.
- `partial` (string): The input digits, echoed back.

## Diagnostics

Captured diagnostic sections: TLS, DNSSEC, Authorisation, Transports. The full working is on the page: https://verifymcp.io/servers/dev-toolstop-check-digits/check-digits#diagnostics

## Score history

- 2026-08-13: 58
- 2026-08-12: 57
- 2026-08-11: 57
- 2026-08-10: 56
- 2026-08-09: 55
- 2026-08-08: 55
- 2026-08-07: 54

## Links

- Remote endpoint: https://check-digits.toolstop.dev/
- Repository: https://github.com/toolstop/toolstop
- Website: https://check-digits.toolstop.dev/
- Changelog RSS feed: https://verifymcp.io/servers/dev-toolstop-check-digits/check-digits.xml
- Changelog JSON feed: https://verifymcp.io/servers/dev-toolstop-check-digits/check-digits.json
- HTML version of this page: https://verifymcp.io/servers/dev-toolstop-check-digits/check-digits