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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds genuinely useful boundary context: payment happens on simorago.com in a browser and this tool performs no purchase, and it discloses that the response carries a purchasable flag indicating whether checkout is currently open.

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?

Two sentences, front-loaded with the core action and followed by the purchase-boundary clarification and routing hint. Slightly awkward phrasing ('with purchasable') but no wasted sentences.

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?

For a simple two-parameter read tool with no output schema, the definition covers the action, the non-transactional nature, the purchasable return signal, and the sibling routing. Only minor gaps remain, such as what happens if checkout is closed or a plan id is invalid.

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%, including the plan_id provenance note and the locale enum, so the schema does the heavy lifting. The description only restates 'for one plan' and adds no syntax, format, or fallback details beyond the schema, which is the baseline 3.

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 and resource (get the simorago.com checkout page link for one plan) and clarifies what the result includes (purchasable flag). It also explicitly distinguishes itself from the purchase action and from search_plans, so an agent can identify it without opening the 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?

Explicitly says when to use it (someone wants to buy a plan found with search_plans), naming the natural predecessor tool. It lacks an explicit when-not clause, but the 'this tool does not buy anything' line implicitly bounds the usage.

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