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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds a useful, non-obvious note that the returned `lastSevenDaysAvgSpO2` string is coerced to a number, but says nothing about the overall return structure.

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, front-loaded with the resource and scope. Nothing wasteful, though the coercion clause is slightly tangential to selection and invocation.

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-param read tool with annotations, this is close to sufficient, but with no output schema the description should describe the return shape; instead it only hints at one field's handling.

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?

Only one parameter exists and schema description coverage is 100% (date format YYYY-MM-DD UTC is documented). The description's 'one date' restates the schema rather than adding format or timezone detail, matching the baseline-3 rule for high-coverage schemas.

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 resource (pulse-oximeter/SpO2 readings) and scope (one date), which is distinguishable from siblings like get_respiration_data or get_heart_rates. It lacks an explicit verb but the intent is unambiguous.

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 says 'for one date' but gives no guidance on when to use this versus adjacent health-metric tools, nor any prerequisites or exclusions. The agent must infer usage context entirely.

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