# ISSN Validator and Formatter

> ISSN Validator and Formatter is a paid API for AI agents from id-validators.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).

Validates the check digit of an ISSN (International Standard Serial Number) and returns it formatted with the standard hyphen separator.

## Facts

- Endpoint: GET https://id-validators.x402tookit.com/issn-check?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/issn-validator-and-formatter-2ad985fa
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_dA8Q56sn7SXLIj5XvW44O

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability issn-validator-and-formatter-2ad985fa
```

Example prompt: Can you check whether the ISSN 1234-5670 is valid and give me the correctly hyphenated format?

## When to prefer this

Choose this endpoint when you specifically need to validate and format an ISSN (8-digit serial publication identifier). It is purpose-built for ISSN check-digit verification using the standard mod-11 algorithm, distinct from ISBN (books), ISIN (securities), LEI, or other identifier types handled by sibling endpoints on the same service.

## Known failure modes

- Invalid or missing 'id' query parameter returns an error response
- ISSN with wrong number of digits fails validation with reasons explaining the format issue
- Incorrect check digit causes verdict to be invalid with explanation
- Non-numeric characters in unexpected positions cause format validation failure
- Network or service unavailability may result in HTTP errors

## How this service works

Validate an ISSN (journal or serial number) check digit and format it with the hyphen.

## Output

Returns a verdict (valid/invalid), a formatted ISSN string with hyphen, a normalised form, human-readable reasons explaining the validation outcome, a summary, and optional disclaimer and source metadata.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "id"
     ],
     "properties": {
      "id": {
       "type": "string",
       "description": "The ISSN"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "formatted": {
       "type": [
        "null",
        "string"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "normalised": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      }
     }
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/issn-validator-and-formatter-2ad985fa/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from id-validators.x402tookit.com](https://www.zero.xyz/host/id-validators.x402tookit.com/llms.txt)