fitbit_compare

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

Annotations already establish read-only, non-destructive, open-world behavior, so the bar is lower. The description adds genuine value beyond them: it discloses the computation method (paired-day means plus coverage) and explicitly disclaims inventing a medical/recovery score, which is meaningful framing for a health-metrics 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?

Three short sentences, front-loaded with the core purpose and method. No filler; the disclaimer sentence earns its place by preempting a wrong expectation about output.

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 and no parameter descriptions, the description covers the concept and default window behavior but leaves the domains filter, output shape, and the exact pairing semantics of explicit previous dates unexplained. Adequate, not complete.

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 0% across 5 parameters, so the description must carry the load. It explains the non-obvious default pairing logic for previousStartDate/previousEndDate (same length as the primary window), which is the most semantically tricky part, but says nothing about the domains parameter or the date format.

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 action (compare) and resource (equal calendar windows) with the method stated (code-calculated paired-day means and coverage). It is reasonably distinct from generic siblings like fitbit_summary or fitbit_read, though it never explicitly names what it is not.

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?

"Defaults to the preceding window of the same length" implies the intended comparison workflow, but there is no explicit when-to-use statement, no prerequisite, and no pointer to an alternative sibling tool for adjacent tasks.

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