---
title: Agent Preflight
description: Agent Preflight lets an agent check a planned tool call before spending on it. It returns allow, block, reuse, defer, or advise. It never executes the destination tool.
---

# Agent Preflight

Agent Preflight lets an agent check a planned tool call before spending on it. It returns allow, block, reuse, defer, or advise. It never executes the destination tool.

## Facts

- What it does: evaluates one planned tool call (supported: `search:web_search`, `browse:fetch`) against your budget and recent history, and returns a decision.
- What it does not do: execute the destination tool, run searches, fetch pages, or return results. You execute the tool yourself.
- Version: v0.3
- Paid endpoint: `POST https://api.agent-preflight.com/v0.2/preflight/tool-call`
- Price: $0.002 USDC per paid POST.
- Payment: x402 v2. Network: Base mainnet (`eip155:8453`). Asset: USDC.
- Unpaid POST: HTTP 402 with a `PAYMENT-REQUIRED` header. Sign locally, retry with `PAYMENT-SIGNATURE`, read `PAYMENT-RESPONSE`.
- Free interfaces: `GET https://api.agent-preflight.com/health`, `GET https://api.agent-preflight.com/openapi.json`, `POST https://api.agent-preflight.com/check-request`, MCP `https://api.agent-preflight.com/mcp`.
- No safety, savings, or downstream-success guarantee.

## Decisions

- `allow`: No rule found waste; the caller decides whether to execute. Not a success guarantee.
- `block`: Inspect the reason: invalid request or terminal retry cap. Unsupported operations instead receive advisory abstention.
- `reuse`: Skip a new call and reuse a recent successful result when available.
- `defer`: Do not execute now; usually budget-infeasible or not worth spending yet.
- `advise`: Optional scope advice; payload unchanged. Paid HTTP consultations still cost $0.002.

## Minimal request body

~~~json
{
  "runId": "settlement-check-01",
  "stepId": "paid-call-01",
  "tool": {
    "provider": "search",
    "operation": "web_search",
    "request": {
      "query": "Acme Corp Series B funding",
      "max_results": 5
    },
    "estimatedExternalCostUsd": 0.01,
    "estimatedModelCostUsd": 0.002
  },
  "budget": {
    "remainingUsd": 0.08,
    "reservedUsd": 0.02,
    "maxToolCallsRemaining": 4
  },
  "task": {
    "goalHash": "settlement-verification"
  },
  "history": []
}
~~~

## Next

- Full guide: https://agent-preflight.com/docs/index.md
- OpenAPI 3.1: https://api.agent-preflight.com/openapi.json
- Agent Skill: https://agent-preflight.com/.well-known/agent-skills/agent-preflight/SKILL.md
- API catalog: https://agent-preflight.com/.well-known/api-catalog