# Particle Pro – List Topics

> Particle Pro – List Topics is a paid API for AI agents from api.particle.pro, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-14).

Returns the hierarchical topic taxonomy, supporting navigation by parent, ancestry path, and pagination.

## Facts

- Endpoint: GET https://api.particle.pro/v1/topics
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/particle-pro-list-topics-38f6c543
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_6xkVMK7ddJDlkXZpniUzO

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 particle-pro-list-topics-38f6c543
```

Example prompt: Show me all the top-level topic categories available in Particle Pro, and then list the subtopics under 'Politics'.

## When to prefer this

Choose this endpoint when you need to discover or navigate Particle Pro's topic taxonomy — whether listing root-level categories, drilling into children of a specific topic, or filtering by ancestry path. It is the authoritative source for topic structure on Particle Pro, useful before querying topic-scoped content like bills, podcasts, or publisher data.

## Known failure modes

- Invalid parent_id returns 404 or empty result
- Invalid ancestry_path hash returns empty list
- Malformed cursor causes pagination error
- Exceeding rate limits returns 429
- Missing required input wrapper causes 400 validation error

## How this service works

List topics. Returns the hierarchical topic taxonomy.

## Output

A paginated list of topic objects from Particle Pro's hierarchical taxonomy, each including a topic ID, name, ancestry slug or path hash, and positional metadata for navigating parent-child relationships. Supports cursor-based pagination for large taxonomies.

## 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",
     "properties": {
      "limit": {
       "type": "integer",
       "format": "int64",
       "description": "Results per page"
      },
      "cursor": {
       "type": "string",
       "description": "Opaque pagination cursor from previous response"
      },
      "parent_id": {
       "type": "string",
       "description": "Get children of this topic. Accepts topic ID, ancestry slug, or ancestry path hash. Omit for top-level roots."
      },
      "ancestry_path": {
       "type": "string",
       "description": "Filter by exact ancestry path hash."
      },
      "ancestry_path_prefix": {
       "type": "string",
       "description": "Filter by ancestry path prefix (all descendants)."
      }
     }
    }
   },
   "additionalProperties": false
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/particle-pro-list-topics-38f6c543/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.particle.pro](https://www.zero.xyz/host/api.particle.pro/llms.txt)