# API Direct – Search Substack Notes

> API Direct – Search Substack Notes 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).

Search Substack Notes by keyword, with optional AI sentiment analysis using Plutchik's Wheel of Emotions

## Facts

- Endpoint: GET https://x402.apidirect.io/v1/substack/notes?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-search-substack-notes-2a2ebfcc
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_2c32TT6rYOJz8AWRqO0o5

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-search-substack-notes-2a2ebfcc
```

Example prompt: Search Substack Notes for 'AI regulation', give me the top 2 pages sorted by most recent, and include emotion analysis so I can see how writers are feeling about the topic.

## When to prefer this

Use this endpoint when you need to search the Substack Notes feed specifically — the short-form social content on Substack, distinct from full newsletter posts or author profiles. Choose this over Substack author search when you want content/notes rather than profile discovery. The optional AI emotion analysis (Plutchik's Wheel) makes it uniquely suited for sentiment research without needing a separate NLP call. Prefer it when you need paginated, high-volume keyword retrieval across Substack's notes ecosystem.

## Known failure modes

- No results found for obscure or misspelled keywords
- Rate limiting or payment failure if insufficient USDC balance
- Requesting more pages than available results (fetching stops early)
- Query exceeds 500-character limit
- Invalid sort_by value other than 'most_recent' or 'top'
- Pages value outside 1–250 range causing validation error

## How this service works

Search Substack Notes by keyword.

## Output

Returns a merged list of up to 12 notes per page (up to 250 pages) from Substack Notes matching the keyword. Each note includes content, author, and publication details. If sentiment analysis is enabled, each note also includes Plutchik's Wheel emotion scores, dominant emotion, emotional intensity, and polarity (positive/negative).

## 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": [
      "query"
     ],
     "properties": {
      "pages": {
       "type": "integer",
       "default": 1,
       "maximum": 250,
       "minimum": 1,
       "description": "Number of pages to fetch and merge into one response (1-250, billed per page returned). Each page returns up to 12 notes. Fetching stops early when there are no more results."
      },
      "query": {
       "type": "string",
       "maxLength": 500,
       "description": "Search keyword (max 500 characters)."
      },
      "sort_by": {
       "enum": [
        "most_recent",
        "top"
       ],
       "type": "string",
       "default": "most_recent",
       "description": "Sort order"
      },
      "get_sentiment": {
       "type": "boolean",
       "default": false,
       "description": "Set to true to add AI emotion analysis (Plutchik's Wheel) to each result. Adds +$0.001 per page to the cost. Returns emotion scores, dominant emotion, intensity, and polarity."
      }
     }
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/api-direct-search-substack-notes-2a2ebfcc/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)