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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), and the description adds genuinely new behavior: daily collection cadence with possible lag on package-download windows, and the guarantee that missing history is reported as a fact rather than a manufactured zero. That staleness/absence semantics is exactly the kind of context annotations cannot express; only exact scope-of-freshness details (timezone of the day boundary) are left implicit.

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?

The verb-and-resource claim is front-loaded, followed immediately by scope, then caveats, then routing. Every clause carries information — the parenthetical and the 'never a fake zero' line both convey real semantics rather than filler.

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 an output schema present, the description doesn't need to explain return values, and it covers read-only safety, data freshness, absence handling, and sibling routing. The one remaining hole is the sole input parameter, which neither schema nor description fully specifies.

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%, so the description carries the full burden for `as_of`, and it never names or explains it. 'For one day' hints at day-level granularity, but the accepted format, whether a null default means today, and how a non-current date is handled are all left unstated.

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 and resource ('Snapshot every observatory metric for one day') and enumerates what the snapshot contains (window values with formula, basis, per-metric history depth). It explicitly contrasts itself with get_market_overview and the get_*_summary siblings, so an agent can place it in the family without opening a 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?

Gives a positive trigger ('Use when the user asks for the current state of the AI agent ecosystem') and two named exclusions routing to get_market_overview for narrative and get_*_summary for a single domain. The when/when-not/alternative triple is fully explicit.

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