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Agent Preflight Tool-Call Evaluator
x402
Agent Preflight Tool-Call Evaluator is a paid API for AI agents from api.agent-preflight.com, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-13).
Evaluates whether an AI agent should proceed with a metered search or browse tool call, considering budget, history, and deduplication — without executing the external tool.
Price / call$0.002
Success—
StatusUnknown
How this service works
Pre-execution decision for a metered search or browse tool call. Evaluates the proposal; does not execute the external tool.
Output
A preflight verdict indicating whether the agent should proceed with the planned tool call, along with signals for deduplication (whether this call was already made), budget adequacy, and any blocking reasons — all without actually executing the external search or browse operation.
Example use cases
Budget gate before web search
“I'm about to run a web search for 'latest Fed interest rate decision' — estimated cost is $0.005 and I have $0.12 left in my budget. Should I go ahead with it? My run ID is 'run-99' and this is step 2.”
Deduplication check before re-fetching URL
“I want to fetch https://example.com/earnings-report before processing it, but I think I may have already done this earlier in the run. Check my call history and tell me if I should skip it — run ID is 'run-77', step 5, estimated cost $0.008.”
Cost guard for agent with tight token budget
“My agent is on step 8 of run 'run-007' and wants to do a web_search for 'climate policy EU 2024' with max 5 results and an estimated external cost of $0.003. I only have $0.02 remaining — should the agent proceed or abort?”
Technical details
Endpoint
POSThttps://api.agent-preflight.com/v0.2/preflight/tool-call?utm_source=zero.xyzWhen to prefer
Use this endpoint when your AI agent is about to execute a metered external tool call (search or web browse) and you need a lightweight, fast pre-execution gate that checks budget sufficiency, deduplication against call history, and overall worthiness — before incurring real costs. Prefer this over executing blindly when running multi-step agentic workflows where tool call costs accumulate, when the same URL or query might be fetched multiple times across steps, or when you need auditable go/no-go decisions logged per step.
Side effects
- Missing required fields (goalHash, provider, operation, estimatedExternalCostUsd, remainingUsd) returns validation error
- Unsupported provider or operation values return an error indicating unsupported tool
- Remaining budget of zero or below estimated cost likely returns a block decision
- Malformed history entries may cause the request to be rejected
- Payment not provided or x402 payment failure results in 402 response before evaluation occurs
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| task | object | |
| tool | object | |
| runId | string | Caller-scoped run identifier |
| budget | object | |
| stepId | string | Caller-scoped step identifier within the run |
| history | array | At most 100 caller-owned prior outcomes; reuse requires explicit permission, positive freshness TTL and matching nonempty goal hashes. |
| retryCap | integer | |
| capabilities | object | |
| preflightPriceUsd | number | Modeled actionable fee only; cannot change the actual HTTP settlement price. |
| freshnessTtlSeconds | number | Explicit positive TTL required for reuse. Omitted or zero disables reuse. |
Tags
x402
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