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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint. The description adds meaningful behavior beyond those: 'Aggregate counts only; no leaked records' clarifies it never returns raw records, and 'plus the five largest incidents ever recorded' discloses an extra output. These traits are not covered by annotations, so the description adds useful transparency.

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 tightly packed sentences: first states capability and dimensions, second gives real usage examples and a clear boundary. No filler or redundancy; every phrase earns its place.

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 no output schema, the description reasonably conveys return shape ('incidents and accounts exposed per year...' plus five largest incidents). It addresses complexity with examples and the no-leaked-records caveat. Slight gap is not detailing limit behavior or bucket ordering, but those are covered in the schema, so remaining context is sufficient.

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 covers 100% of parameters with detailed descriptions, including default values, min/max, and semantic notes (e.g., limit buckets_total behavior). The tool description adds no new parameter-specific meaning beyond restating group_by options already in the schema, so baseline 3 is appropriate.

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?

Description uses specific verb 'Aggregate' with clear resource 'full breach archive' and enumerates exact output dimensions (per year, source, data type, threat level, actor). It differentiates from siblings via 'Aggregate counts only; no leaked records' and answers concrete analyst questions, making purpose unambiguous.

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?

Provides explicit when-to-use guidance via example questions ('how has breach volume trended...', 'which ransomware groups...'). While it doesn't name alternative tools or state when not to use it, the context is clear enough for an agent to select it over the listed siblings.

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