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 useful context beyond that: this is an aggregate over an already-stored dataset (not a live scrape), and it names the metric families the payload contains. It does not mention rate limits or freshness/lag of the aggregates, which would have pushed it to 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?

Two sentences, front-loaded with the core purpose and the payload contents before the routing advice. No filler, no restatement of the tool name.

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, return format need not be explained, and annotations cover the safety profile; the description supplies purpose, contents, alternatives, and the key parameter. The only gap is the undocumented `limit` parameter and no guidance on the changes/history/trending siblings, which is minor for a 2-param aggregate tool.

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 100%, so the schema already documents both `days` (7/30/90, default 30) and `limit` (default 10, min 5, max 25). The description repeats the `days` enum but adds no meaning beyond it and never mentions `limit`, so it neither compensates nor extends the schema. Baseline 3 is correct.

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?

Specific verb ('Return aggregate metric data') plus a named resource ('the stored Chrome Web Store dataset'), and it enumerates the metric families returned: coverage, adoption, ratings, permissions, privacy, recent changes. It also actively distinguishes itself from two siblings by name, so an agent can tell it apart 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 explicit routing: 'use datasets_chrome_extensions_facets for filter distributions or datasets_chrome_extensions_item for one snapshot', and clarifies that `days` selects the window. It stops short of covering the other closely named siblings (changes, history, trending), and 'recent changes' in the payload overlaps semantically with datasets_chrome_extensions_changes, leaving a small ambiguity about which to call for change data.

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