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

The readOnlyHint annotation already establishes this is a safe read, so the description is not carrying the safety burden. It adds the concrete endpoint (GET .../date/{date}.json), which hints the '-' segment is the authenticated user, but says nothing about what the response contains or whether an empty day returns an error.

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 short sentences with the purpose front-loaded before the endpoint reference. Efficient, though the raw REST path is arguably redundant scaffolding for an agent that only needs the semantic intent.

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 trivial one-parameter read tool whose safety profile is covered by annotations and whose parameter is fully described in the schema, the description is essentially sufficient. Only the missing guidance on date/response behavior keeps it from being fully 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 coverage is 100% and the single date parameter is fully documented (yyyy-MM-dd or 'today'), so the baseline is 3. The description only restates the same date concept via the URL template and adds no format or edge-case detail beyond the schema.

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 the resource (water intake log) and scope (for a date), and the REST endpoint confirms it is a retrieval. It distinguishes itself from the many other *_log siblings (food_log, sleep_log, weight_log) by naming the water resource, though it never explicitly frames the verb as 'retrieve' vs 'create'.

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?

No guidance on when to use this versus fitbit_food_log or the other log tools, no mention of date-range constraints, and no note that this requires an authenticated user ('-' placeholder is unexplained). The agent must infer usage entirely from context.

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