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

Annotations already declare readOnly, idempotent, non-destructive. The description adds context about what the aggregate covers (totals by status/type/priority plus overdue) and that it avoids paging, which is useful behavioral information. It doesn't disclose pagination or output format, but for a read-only aggregate that's minor.

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?

Four sentences, each earning its place: scope, value proposition, clarification of scope, and routing to the alternative tool. Front-loaded with the main purpose.

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?

Given single parameter, full schema coverage, and read-only annotations, the description explains what the tool returns at a high level. It doesn't specify the exact structure of the aggregates, but no output schema exists and the description names the groupings sufficiently for an agent to understand what it gets.

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?

With 100% schema coverage and a single parameter, the schema fully documents project_id. The description reinforces that it's a single project and hints at omission to list projects, but the schema already states that. Baseline 3 plus slight value from clarifying scoping, thus 4.

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?

The description opens with a specific verb and resource ('Aggregate counts for one project'), enumerates the exact groupings (status, type, priority, overdue), and contrasts itself with list_tasks and get_project_structure, distinguishing it from siblings.

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?

Explicit when-to-use (answers 'how is this project doing' in one call) and when-not-to-use (for per-epic breakdowns, get_project_structure is the only tool), naming the alternative directly.

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