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

The annotations only say readOnlyHint=true and openWorldHint=false; the description earns credit by explaining why that is true (payment happens in the user's own browser, the tool merely hands back a link) and by disclosing the shape of what comes back — link, instructions, post-purchase outcome, and a user-facing message. It stops short of covering failure cases such as an unavailable plan or how long the link stays valid.

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?

Four short sentences, front-loaded with the core behavior and followed by the prerequisite and the safety rule. Each sentence contributes a distinct, actionable fact with no restatement of the name or title.

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 takes responsibility for describing the return payload, and it does so in categories an agent can act on. Both parameters are fully documented in the schema, so nothing an agent needs to call this tool correctly is missing.

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% and the enum spells out all seven plan values, so the schema already carries the semantic load. The description adds only sequencing context (pick a plan via list_plans first) and says nothing new about audit_result_url, so the 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?

The description states a specific verb and resource — starting a purchase of an Agency Growth plan — and immediately clarifies what the tool actually produces: a single link the user opens. It is distinguishable from list_plans, run_ai_audit and the other siblings, which are all informational tools, 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?

It gives an explicit prerequisite ("Call list_plans first if the user has not picked a plan") and an explicit prohibition ("Never enter card details for the user"), so both the sequence and the boundary of agent action are stated rather than inferred. The condition that selects list_plans over this tool is named directly.

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