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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and non-destructive behavior, covering the safety profile. The description adds valuable context beyond this: it discloses the exact return structure and notes the optional _apiKey parameter for higher rate limits, which is a behavioral consideration. It does not contradict the annotations.

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 two sentences plus an example, with no wasted words. The core purpose is stated first, followed by the return format, and the example is appended naturally. It is well-structured and easy to parse.

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 read-only query tool with no output schema, the description is complete. It covers all filter options, the return format, and even hints at API key usage for rate limits. An agent has everything needed to call the tool correctly, given the annotations already establish safety and idempotency.

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%, so all parameters are already documented. The description reinforces the usage pattern with an example but adds little semantic detail beyond what the schema provides. The example is helpful for understanding typical filter combinations, but the schema already explains each parameter's meaning and allowed values.

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 tool's purpose: retrieving fitness/gym exercises filtered by muscle, type, difficulty, or name. It specifies the return format and provides an example, making the action and resource unambiguous. The sibling list contains no similar fitness tool, so it stands out distinctly.

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 includes a concrete usage example (exercises({ muscle: 'biceps', difficulty: 'beginner' })) that demonstrates how to invoke the tool. It does not explicitly state when not to use it or mention alternatives, but the specificity and example make the intended use clear. Since no sibling tool competes for this domain, the lack of exclusions is acceptable.

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