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

Goes far beyond annotations: explains that it orders and charges nothing, later deliveries are new orders with the same discount, emails five days before, no automatic card payments, and pause/resume/cancel is possible. Also notes the 'eligible' false case with a reason. This is rich behavioral context that annotations alone do not cover.

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?

Well-structured and front-loaded, but somewhat long and dense. Every sentence adds value, though it could be trimmed slightly without losing meaning.

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?

Complete: purpose, usage, return values (subscriber price, frequency, link), what it does not do, ongoing behavior, and eligibility failure are all covered. With an output schema present, no further return value explanation is needed.

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 100%, so baseline is 3, but the description adds meaning by explaining that the id can be a product id from find_products or a teas.co.uk product link, and the limit 'one product id' reinforces the single-parameter constraint.

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?

Specific verb+resource: starts a repeat delivery subscription for a teas.co.uk product. It clearly distinguishes from siblings like add_to_basket or checkout_session by describing the subscribe-and-save flow.

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 states when to use it ('when someone wants a teas.co.uk product delivered again and again'), what to pass (one product id from find_products or a link), and what it does not do ('orders and charges nothing'). It also names related tools for managing the subscription (my_subscriptions, change_subscription).

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