Google Flights Policy Recommender (MCP)

Start booking a flight (stops before payment)

start_booking

Re-validates a flight against policy, fills traveler details on the airline site, and stops before payment. Returns a report of what was filled and where human needs to take over. Refuses booking if out-of-policy unless acknowledged.

Instructions

Re-validates the chosen flight against policy, then drives Google Flights through fare selection to the airline/OTA site and best-effort fills traveler details. ALWAYS stops before any payment field or purchase button — it never enters payment info or completes a purchase. Returns a report of what was filled, what wasn't, and the URL/screenshot where a human needs to take over. If the flight is out of policy, booking is refused unless acknowledgeOutOfPolicy is explicitly set to true.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "flightId": "<flightId>",
      "traveler": "<traveler>"
    },
    "name": "start_booking"
  }
}

Input Schema

Name	Required	Description	Default
`flightId`	Yes	A flight id returned by search_flights
`traveler`	Yes
`fareChoice`	No	Which fare tile to pick on the airline's booking-options panel	cheapest
`policyPath`	No		./policy.json
`acknowledgeOutOfPolicy`	No	Must be explicitly true to proceed with a flight that fails policy checks

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Jul 14, 2026

TDQS

A4.4/5.0

Behavior4/5

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

With no annotations, the description fully covers behavior: it never enters payment info, re-validates policy, best-effort fills details, and returns a report. It also explains the out-of-policy refusal condition.

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

Conciseness5/5

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

Three sentences, front-loaded with the core action, no wasted words. Each sentence adds critical 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?

The description covers the tool's workflow, return value (report with URL/screenshot), and policy interaction. Without an output schema, it provides sufficient expectations for the agent.

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

Parameters4/5

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

The description adds context beyond the schema for key parameters like fareChoice (explains fare tile selection) and acknowledgeOutOfPolicy (explains its role in overriding policy refusal). For traveler and flightId, it supplements the schema by describing their roles.

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

Purpose5/5

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

The description clearly states the tool re-validates the flight, fills traveler details, and stops before payment. This differentiates it from sibling tools like check_policy or search_flights, which handle specific sub-tasks.

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 explains when to use the tool (after selecting a flight, before payment) and conditions for refusal (out-of-policy without acknowledgeOutOfPolicy). It does not explicitly mention alternatives but implies that a human must take over after this step.

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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