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

Annotations declare readOnlyHint=false and idempotentHint=false, but the description adds real substance beyond them: it discloses the authorization chain (verify stock, lock quote, authorize payment) and a hard security constraint ('Never send raw card numbers'). It stops short of stating irreversibility, charge semantics, or failure/rollback behavior.

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 short sentences, front-loaded with the action, then the accepted token form, then the internal steps. No filler; each clause carries information the agent needs before calling.

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?

With an output schema present, return values need no explanation, and annotations cover the safety profile. The description supplies the payment-token requirement and the multi-step side effects, leaving only edge behavior (declines, partial failure, whether the quote lock expires) unaddressed for a high-impact mutation.

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?

Schema coverage is 80%, so the schema already documents most parameters including the pm_* token format it repeats in the description. The description adds little syntax or meaning beyond what the schema provides, so baseline 3 applies.

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?

States a specific verb+resource ('Execute ... checkout') and distinguishes itself from start_checkout by emphasizing it completes the purchase outright ('zero-click autonomous checkout'), plus enumerates the internal steps (stock verify, quote lock, payment auth). An agent can tell this apart from a flow-starting sibling without opening either schema.

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?

Usage is implied rather than stated: the payment-method constraint tells the agent a token must already exist, and the schema's store_id note ties usage to an eligible offer, but the description never names start_checkout as the prerequisite alternative or states when-not to call this. Adequate context, no explicit routing.

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