# API Direct – Substack Publication Lookup

> API Direct – Substack Publication Lookup is a paid API for AI agents from x402.apidirect.io, paid per call via x402, $0.004/call, status unknown (last checked 2026-10-30).

Retrieve detailed metadata about a Substack publication by its subdomain, custom domain, full URL, or numeric publication ID.

## Facts

- Endpoint: GET https://x402.apidirect.io/v1/substack/publication?utm_source=zero.xyz
- Price: $0.004/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-30
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/api-direct-substack-publication-lookup-4eded6ce
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_mEDkXcuqLhGy23TNabpN9

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 api-direct-substack-publication-lookup-4eded6ce
```

Example prompt: Can you look up the Substack publication details for lenny.substack.com and tell me its publication ID and any other metadata you get back?

## When to prefer this

Use this endpoint when you need to resolve a Substack newsletter's identity — converting a subdomain, custom domain, URL, or numeric ID into full publication metadata. It is the right choice when you have a partial identifier (e.g. just a domain from a link) and need the canonical publication ID for use in downstream Substack API calls, or when you want to verify that a given Substack publication exists and retrieve its profile details.

## Known failure modes

- Publication not found for the given subdomain or domain — returns an error or empty result
- Invalid or malformed URL/subdomain input — may return a validation error
- Numeric publication_id does not correspond to any known publication — returns not-found error
- Neither publication nor publication_id provided — request rejected due to missing required parameter
- Rate limiting or payment failure (x402 payment not processed) — returns 402 Payment Required

## How this service works

Get a Substack publication by subdomain, custom domain, URL or ID.

## Output

Returns structured metadata about the matched Substack publication, including its publication ID, name, subdomain, custom domain (if any), and other profile information such as description, author details, and subscriber-related fields.

## 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",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [],
     "properties": {
      "publication": {
       "type": "string",
       "maxLength": 500,
       "description": "Publication subdomain (lenny), host (lenny.substack.com, www.lennysnewsletter.com) or any URL on it (max 500 characters). Provide either publication or publication_id."
      },
      "publication_id": {
       "type": "string",
       "description": "Numeric publication ID, as returned in publication_id. Provide either publication or publication_id."
      }
     }
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/api-direct-substack-publication-lookup-4eded6ce/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from x402.apidirect.io](https://www.zero.xyz/host/x402.apidirect.io/llms.txt)