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

readOnlyHint=true already tells the agent this is a safe, non-mutating call. The description adds useful context by enumerating the returned fields and citing the underlying REST endpoint, but says nothing about auth requirements, rate limits, or whether the profile can ever be empty.

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?

Two tight sentences: resource identity first, then the field list and endpoint reference. Nothing is redundant and no sentence is wasted.

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, the description appropriately compensates by listing what the profile contains. It is nearly complete, lacking only incidental details such as auth scope or whether the response can be cached, which are minor for a zero-param read.

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?

The tool takes zero parameters, so the baseline is 4. The description correctly implies no input is required by framing this as fetching 'the current user's' profile ('- ' in the REST path), but there is no schema-level content for it to add to.

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?

States a specific verb (get) and resource (the current user's Fitbit profile), and enumerates the fields returned (name, age, gender, height, timezone, member since, avatar). This differentiates it from all sibling tools, which are activity/sleep/body-data logs rather than account metadata, though it does not name a sibling explicitly.

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?

Usage is implied rather than stated: an agent infers this is the tool for account/profile metadata. There is no explicit when-to-use or when-not-to-use guidance and no mention of alternatives, but for a zero-parameter metadata read the alternatives space is narrow.

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