# Keystone Opportunity API – Brief Check

> Keystone Opportunity API – Brief Check is a paid API for AI agents from keystone-opportunity-api.keystone-opportunity.workers.dev, paid per call via x402, $0.001/call, status unknown (last checked 2026-09-14).

Validates a task brief for autonomous agents, scoring it for completeness and readiness before execution

## Facts

- Endpoint: POST https://keystone-opportunity-api.keystone-opportunity.workers.dev/v1/brief-check
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/keystone-opportunity-api-brief-check-51f2db5a
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_iWm3QEJ8IfuqLE9MeYbrw

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 keystone-opportunity-api-brief-check-51f2db5a -d '<json body>'
```

Example prompt: Before I kick off this job, can you check if my task brief is ready? Here it is: 'Generate a 500-word blog post about EV adoption trends and save it as blog-post.md in the /output folder.'

## When to prefer this

Choose this endpoint when you need a deterministic, low-cost check on a task brief before handing it off to an autonomous agent. Ideal for agentic pipelines that want to catch ambiguous or incomplete instructions early, reducing downstream failures. At $0.001 USDC per call it is cheap enough to run on every brief in a workflow. Prefer this over manual review or LLM self-assessment when you need a consistent, structured scoring rubric with specific named checks.

## Known failure modes

- Brief text is empty or missing — returns 400 with validation error
- Brief exceeds 8000 character limit — returns 400 with length error
- Payment not included or insufficient USDC — returns 402 challenge via x402 protocol
- Malformed JSON body — returns 400 parse error

## How this service works

Low-cost, deterministic x402 utilities for autonomous agents on Base. Every /v1 route is priced in USDC and settles onchain via the x402 protocol; discover and pay programmatically through the x402 Bazaar. No API keys, no subscriptions.

## Output

Returns a JSON object with a boolean 'ready' flag, an integer 'score' (0-100), an array of 'checks' each with an id, passed status, and descriptive message, and a 'characters' count of the brief. Agents can use the score and failed checks to iteratively improve the brief before execution.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "brief": {
   "type": "string",
   "maxLength": 8000,
   "minLength": 1,
   "description": "Task brief to validate."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ready": false,
  "score": 80,
  "checks": [
   {
    "id": "deliverable",
    "passed": true,
    "message": "Name the exact file, artifact, or outcome to deliver."
   }
  ],
  "characters": 121
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/keystone-opportunity-api-brief-check-51f2db5a/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from keystone-opportunity-api.keystone-opportunity.workers.dev](https://www.zero.xyz/host/keystone-opportunity-api.keystone-opportunity.workers.dev/llms.txt)