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

Beyond the sparse annotations (readOnly=false, destructive=false, idempotent=false), the description discloses meaningful behavior: price is deterministic, the quote thread is created directly in accepted state, the charge is immediate, funds are held in escrow, payout releases on acknowledgement or after 7 days, and delegation/envelope enforcement matches services_accept_quote. This gives the agent a realistic model of side effects and timing.

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

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

Three sentences carry a high density of relevant information: what the call does, how escrow and payout work, and which sibling tools are involved. The core purpose is front-loaded in the first sentence, and every clause adds operational value without redundancy.

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

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

The description gives a complete end-to-end picture of the purchase flow—validation, pricing, charging, escrow, delivery, and payout—and references the enforcement model of a sibling. It does not describe the return value or explicitly walk through the confirmation_required retry flow, but those details are present in the schema, and the lifecycle coverage is strong enough for an agent to call the tool correctly.

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

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

The input schema already describes all 7 parameters (100% coverage), including the scope's metered field, payment method defaults, confirmation token, and test-only outcome. The description reinforces that scope is validated and that price is computed, but it does not add per-parameter meaning beyond the schema, so it sits at the baseline for high schema coverage.

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

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

The description opens with a specific verb and resource: 'Buy a fixed-price service in one call,' then enumerates the full action sequence (validates scope, computes deterministic price, creates accepted quote thread, charges immediately). It distinguishes itself from the quote-based sibling flow by stating 'no seller round-trip' and explicitly references services_accept_quote for enforcement context.

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

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

The description clearly indicates this is for immediate, fixed-price purchases without seller negotiation ('in one call', 'no seller round-trip') and orients the agent within the broader lifecycle by naming services_submit_deliverable and services_acknowledge_delivery. It does not explicitly state when-not-to-use or name an alternative for quote-based negotiation, so it stops short of a full 5.

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