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

With no annotations, the description carries the burden well: it discloses the OAuth scope history:read and, importantly, the negative semantics that a date missing from records means nothing was measured rather than insufficient sun — a distinction that prevents a real misinterpretation. The trailing sentence about rendering a tappable calendar is ambiguous about whether tapping writes data, which keeps it from a 5.

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?

Front-loaded and dense with genuinely useful content — the payload summary, the missing-record caveat, and the auth scope all earn their place. However, the `from`/`to` clause is wasted (and wrong) text that forces the agent to reconcile the description against the schema.

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 single-parameter read tool with no output schema, the description covers most of what an agent needs: scope, auth, and the interpretation of absent records. The gap is that it never explains the actual `days` window semantics (how far back, what the 365 cap means for the response), substituting a nonexistent date range instead.

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 description references `from` and `to` date boundaries, but the schema exposes a single `days` integer with a default of 30 and a 1-365 range — no `from`/`to` parameters exist. This actively misleads the agent about the input shape. The schema's 100% coverage of `days` prevents a lower score, but the invented parameters are a substantive defect.

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 and owner: the signed-in user's sun history from the app calendar, plus the three things it contains (viable days, confirmed days, current streak). That is distinguishable from siblings such as get_vitamin_d_year or get_current_status without opening either schema.

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 by scope ('the signed-in user's... history') rather than stated: there is no explicit 'use this when X, use sibling Y when Z', even though compare_vitamin_d_year and get_current_status sit adjacent. The OAuth scope note is a useful precondition but not routing guidance.

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