# Substack Publication Recommendations Lookup

> Substack Publication Recommendations 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).

Returns the Substack publications that a given publication recommends to its readers, and the publications that recommend it in return.

## Facts

- Endpoint: GET https://x402.apidirect.io/v1/substack/publication/recommendations?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/substack-publication-recommendations-lookup-73b91b58
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_TGvwAQLfJrMb5gA59_sti

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 substack-publication-recommendations-lookup-73b91b58
```

Example prompt: Can you pull up the list of Substack newsletters that Lenny's Newsletter (lenny.substack.com) recommends to its readers, and also which publications recommend it back?

## When to prefer this

Use this endpoint when you need to explore the editorial recommendation graph of Substack publications — particularly for competitive research, partnership discovery, or newsletter ecosystem mapping. Prefer it over generic web scraping when you need structured, machine-readable recommendation data tied to a specific Substack publication by subdomain, host, or numeric ID.

## Known failure modes

- Publication not found if subdomain/host/URL is misspelled or doesn't exist on Substack
- Missing required input if neither publication nor publication_id is provided
- Empty recommendation lists if the publication has no mutual recommendations set up
- Rate limiting or payment failure if x402 micropayment is not correctly handled
- Stale data if Substack recently changed a publication's recommendation settings

## How this service works

Get the publications a Substack publication recommends to its readers, and the publications that recommend it.

## Output

Returns two lists: (1) publications this Substack recommends to its readers, and (2) publications that recommend this Substack — each entry likely includes publication name, subdomain/host, and publication ID, enabling further graph traversal or filtering.

## 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/substack-publication-recommendations-lookup-73b91b58/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)