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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is fully covered without the description's help. The description adds the useful scope detail that results span the whole archive, but says nothing about cost, caching, or freshness beyond that. This is acceptable added context given the annotation coverage, not more.

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?

One sentence, front-loaded with the verb and resource, then the concrete metrics. No filler, no restatement of the title.

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 need not explain return values, and annotations carry the safety profile. The enumerated metric categories plus the archive-wide scope make it sufficient for a zero-parameter stats tool; only freshness/timing context is absent.

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 tool takes zero parameters, so the baseline is 4; there is nothing for the description to disambiguate. The description correctly avoids inventing parameters and instead documents the shape of the aggregate result.

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 ('Get') plus resource ('screenshot statistics') with the returned metrics enumerated (total screenshots, hash coverage, perceptual hash type distribution). It is clearly distinct from the screenshot search tools (search_by_screenshot_hash, search_similar_screenshots), but it never explicitly contrasts itself with any sibling the way a 5 would.

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 phrase 'across the archive' implies this is a global aggregate query rather than a per-scan or filtered lookup, which is the only usage signal present. There is no explicit statement of when to prefer this over per-scan or search endpoints, and no prerequisites or exclusions are given.

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