subscribe_to_plan

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It effectively describes key traits: it's a transactional tool ('Pays... from your pre-funded balance'), has temporal effects ('until the period ends'), includes auto-renewal, and requires authentication ('Requires API key'). It lacks details on error handling or rate limits, but covers essential behavior for a subscription tool.

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?

The description is front-loaded with the core action and resource, followed by key details in a logical flow: payment method, access duration, renewal policy, and authentication requirement. Every sentence adds value without redundancy, making it efficient and well-structured.

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?

Given the tool's complexity (a financial transaction with auto-renewal), no annotations, and no output schema, the description provides a solid foundation by covering purpose, payment, access, renewal, and authentication. It could be more complete by mentioning response format or error cases, but it adequately addresses the core context for agent use.

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%, with the parameter 'plan_id' fully documented in the schema. The description does not add any additional meaning or context about the parameter beyond what the schema provides, such as example values or constraints. This meets the baseline score when schema coverage is high.

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 clearly states the specific action ('Subscribe to a plan') and resource ('on the402.ai'), distinguishing it from siblings like 'list_plans' or 'manage_subscription'. It specifies the outcome ('Gives access to all services bundled in the plan until the period ends') and mechanism ('Pays the first billing period from your pre-funded balance'), making the purpose unambiguous.

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 implies usage context by stating 'Requires API key', which suggests authentication prerequisites. However, it does not explicitly guide when to use this tool versus alternatives like 'purchase_product' or 'manage_subscription', nor does it specify exclusions or direct comparisons to sibling tools.

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