agent-embassy

Preflight Check

preflight_check

Idempotent

Use preflight_check before your agent spends on a paid tool or endpoint: the Embassy answers WHO is paid, WHAT is delivered, what CHANGED, the full COST, and WHO TAKES A CUT — then returns a signed PROCEED, PROCEED_WITH_CAUTION, BLOCKED, or UNKNOWN verdict with the full proof envelope. POST the tool inputs as JSON to paid_url with an x402 v2 PAYMENT-SIGNATURE header. See https://docs.cdp.coinbase.com/x402 Paid tool — $0.25, USDC on Base or Arbitrum One. Paid URL: https://aemb.pro/v1/preflight/check.

Input Schema

TableJSON Schema

Name	Required	Description
`intent`	Yes	The intended invocation: operation (required), params_summary (sha256 of canonical params), advertised_cost_usdc
`policy`	No	Policy strings (max 20)
`context`	No	principal_wallet + chain. Optional.
`dry_run`	No	true = free dry-run, intercepted before the payment gate
`subject`	Yes	The spend target: server_id (required), artifact (mcpb:// \| oci:// \| https://), claimed_version
`idempotency_key`	Yes	Idempotency key: UUID v4, client-generated, one per logical request. Replaying the same key on this tool returns the original receipt — the action is not re-run, and the first request's receipt wins even if you resend different inputs. Published example keys are rejected. Keys are scoped per tool and per payer account: a key never returns another wallet's receipt.

Output Schema

TableJSON Schema

Name	Required	Description
`how`	Yes	How to pay: POST the tool inputs as JSON to paid_url with an x402 v2 PAYMENT-SIGNATURE header
`tool`	Yes	Tool name, e.g. verified_check
`asset`	Yes	Settlement asset
`price`	Yes	Exact price, e.g. "$0.15"
`networks`	Yes	EVM CAIP-2 network ids accepted
`paid_url`	Yes	x402-paid HTTPS URL to POST the tool inputs to
`facilitator`	Yes	x402 facilitator
`payment_required`	Yes	Always true: this MCP tool is a payment pointer; the tool itself is monetized via x402.

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedSep 26, 2026

removedInput schema / properties / agent_wallet

Removed value: -{
-  "description": "Dev mode only: declares the account wallet (string, min 20 chars) when no x402 payment is present. Ignored in live mode — there the wallet is recovered from the verified payment authorization.",
-  "type": "string"
-}

changedInput schema / properties / idempotency_key / description

Previous value: -"Idempotency key: any non-empty string (a UUID is recommended; no format is enforced). Replaying the same key on this tool returns the original receipt — the action is not re-run, and the first request's receipt wins even if you resend different inputs. Keys are scoped per tool: the same key on another tool is unrelated."New value: +"Idempotency key: UUID v4, client-generated, one per logical request. Replaying the same key on this tool returns the original receipt — the action is not re-run, and the first request's receipt wins even if you resend different inputs. Published example keys are rejected. Keys are scoped per tool and per payer account: a key never returns another wallet's receipt."

AddedSep 24, 2026

TDQS

A3.9/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The description adds significant behavioral context beyond the annotations: it is a paid operation at $0.25 USDC on Base or Arbitrum One, requires an x402 v2 PAYMENT-SIGNATURE header, POSTs inputs to a specific URL, and returns a signed verdict with a proof envelope. It does not contradict the idempotentHint, and the schema covers idempotency replay behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description front-loads the core purpose and outcome, then supplies cost, network, auth header, and paid URL in compact form. It is slightly run-on and packs many details into dense clauses, but every sentence carries useful operational information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the nested schema and output schema, the description is reasonably complete: it covers purpose, payment cost, network, endpoint, auth mechanism, and verdict type. The main missing piece is explicit when-not-to-use guidance, but the pre-spend framing and dry_run parameter largely compensate.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, with detailed nested descriptions for subject, intent, context, and idempotency_key. The description itself contributes little parameter-level meaning beyond saying inputs are POSTed as JSON, so the baseline of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's function: run a pre-spend check that returns WHO is paid, WHAT is delivered, what CHANGED, the COST, and WHO TAKES A CUT, plus a signed PROCEED/BLOCKED verdict. It is specific about the resource and outcome, though it does not explicitly distinguish itself from sibling verification tools like assurance_check or verified_check.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives an explicit trigger condition: use preflight_check before spending on a paid tool or endpoint. It also gives practical guidance about the paid nature and the dry-run option in the schema, but it does not state when not to use it or name alternatives, so it stops short of a 5.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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