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

Annotations only declare readOnly/openWorld, but the description adds real behavioral context: a Garmin Connect+ subscription prerequisite, the limit cap of 20 that triggers a 400 above it, the 405 on GET /customFood/{id}, and the actual response shape {customFoods, moreDataAvailable}. These are non-obvious constraints that materially change invocation.

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?

Front-loads the precondition and scope, then the hard constraints, with the limit cap bolded for emphasis. It repeats the Connect+ requirement twice ('check with has_connect_plus' and 'Needs Connect+'), a minor redundancy that costs a point.

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 3-param, no-output-schema tool, the description covers auth preconditions, parameter constraints, error behaviors, the single-item read workaround, and the return shape. An agent has everything needed to call it correctly; only 'start' is left implicit.

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 0%, so the description carries the burden. It explains that search filters by name and that limit is hard-capped at 20, adding real meaning over the bare schema. The 'start' parameter (pagination offset) is never explained, leaving one gap.

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?

Names a specific verb+resource ('Your custom foods') and clearly distinguishes from the create_custom_food/update_custom_food/delete_custom_food siblings. An agent immediately knows this is a retrieval tool for the user's own custom food library.

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?

Gives explicit when-to-use context: check has_connect_plus first, and crucially the workaround 'There is NO get-by-id ... so search by name to read one back', which tells the agent exactly how to fetch a single item. This is actionable routing information beyond mere description.

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