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

Annotations already declare readOnlyHint and idempotentHint, so safety is covered. The description adds real behavioral context beyond them: the result always carries a human-vs-bot split regardless of include_bots, and it returns total plus per-repository and per-author breakdowns. It doesn't mention pagination or window caps, but with annotations carrying the safety profile this is a strong addition.

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-loads the core purpose and the key output guarantee in the first sentence, then the trigger condition last. It is somewhat long for three optional parameters and the example slug is slightly redundant with the schema, but no sentence is wasted.

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?

An output schema exists, so return values needn't be explained, yet the description usefully summarizes the shape (total, per-repo, per-author). Combined with annotations covering read-only/idempotent behavior, an agent has enough to call it correctly; only alternative-tool routing is missing.

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 all three parameters are already documented. The description largely restates structured facts ('default 30 days', the include_bots split behavior, 'owner/name' scoping) rather than adding new syntax or edge-case detail, so the baseline 3 applies.

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 ('Count merged pull requests over a recent window') plus the two key dimensions it reports (human-vs-bot split, per-repo/per-author breakdowns). An agent can distinguish this from siblings like get-open-pull-requests-tool 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?

Explicitly supplies the trigger phrasing: 'Use this when the user asks how many PRs were merged, shipped, or closed on a repo or across the team — including bot/dependabot PRs.' That is clear context for invocation, but it never names an alternative sibling (e.g. get-pull-request-metrics-tool) or states when-not to use it, so it falls short of a 5.

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