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

Annotations already declare readOnlyHint=false, idempotentHint=false, and destructiveHint=false. The description adds non-obvious behavior beyond that: issuance occurs the moment payment settles, delivery is by PDF email, and a verifiable hash is registered. It does not cover payment mechanics or failure cases, but the fulfillment model is materially clearer than annotations alone.

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?

Five short sentences, front-loaded with purpose and immediately followed by the sibling distinction and the fulfillment model. Every sentence carries information relevant to selecting or invoking the tool; no filler.

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 no output schema, the description appropriately explains the fulfillment outcome (instant issuance, PDF email, hash registration) and the consent requirement. For a non-idempotent purchase tool, it could say more about payment flow or irreversibility, but the core calling context is present.

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 description coverage is 100%, so the baseline is 3. The description adds some meaning to buyer_confirmed_choice by stressing that the buyer must choose rather than the agent deciding, but it largely overlaps with the schema's own description of that parameter and adds little on email, name, certificate_id, or catalogue_token.

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 concrete verb and resource ("Buy a certificate") and immediately distinguishes it from the nearest sibling ("Use this instead of create_order, which is only for booking time"). The contrast between certificates as objects and appointments as slots further sharpens what this tool is for.

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?

Explicitly names the alternative (create_order) and the condition that selects it (certificate purchase vs. booking time). It also gives a usage rule for the buyer interaction ("show the buyer what is on offer and let them choose"), which tells the agent how to invoke it correctly.

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