# API Direct – Substack User Profile Lookup

> API Direct – Substack User Profile 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).

Retrieves a Substack author's full profile given their handle, numeric user ID, or profile URL.

## Facts

- Endpoint: GET https://x402.apidirect.io/v1/substack/user?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-user-profile-lookup-79a4cb17
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_hnpvihHVkgQvmjpQtVLnW

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-user-profile-lookup-79a4cb17
```

Example prompt: Can you pull up the full Substack profile for the author with the handle 'lenny' — I want to see their bio, subscriber info, and any other profile details?

## When to prefer this

Use this endpoint when you need structured profile data for a specific Substack author and you already know their handle, user ID, or profile URL. Prefer this over Substack publication search when you want author-level details rather than publication search results. Ideal for enriching author metadata, resolving identities, or fetching subscriber counts for known creators.

## Known failure modes

- Unknown username or handle returns 404 or empty result
- Invalid or malformed profile URL returns an error
- Numeric user ID not found returns no data
- Rate limiting or payment failure returns 402 or 429
- Substack profile may be private or deactivated, returning limited data
- Ambiguous handle (with or without leading @) may cause lookup inconsistency

## How this service works

Get a Substack author's full profile by handle, user ID or profile URL.

## Output

Returns the Substack author's full profile object, which typically includes display name, username/handle, numeric user ID, bio/description, profile photo URL, subscriber count, associated publication(s), join date, and other public profile metadata available on Substack.

## 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": {
      "url": {
       "type": "string",
       "maxLength": 500,
       "description": "Profile URL, e.g. https://substack.com/@lenny (max 500 characters). Provide one of username, user_id or url."
      },
      "user_id": {
       "type": "string",
       "description": "Numeric Substack user ID, as returned in user_id. Provide one of username, user_id or url."
      },
      "username": {
       "type": "string",
       "maxLength": 100,
       "description": "Substack handle, e.g. lenny, with or without a leading @ (max 100 characters). Provide one of username, user_id or url."
      }
     }
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/api-direct-substack-user-profile-lookup-79a4cb17/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)