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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is clear. The description adds valuable behavioral context: approximate dataset size (~267 records across ~85 issuers), the types of fields returned, and the fact that this is legally mandated disclosure data. No contradictions with annotations.

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?

The description is appropriately sized and front-loaded with the core purpose, followed by data contents, use cases, and a comparison with the sibling tool. Every sentence adds value, though it could be slightly tightened without losing meaning.

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?

For a read-only tool with an output schema, the description is complete: it explains the data source, coverage, fields, use cases, and relationship to get_shareholders. The annotations cover idempotency and safety, and the schema covers both parameters, so nothing essential is missing for an agent to select and invoke the tool correctly.

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 coverage is 100%, and both parameters are already described in the schema: ticker is an NZX ticker symbol, and include_ceased toggles former substantial holders. The description adds some related context about threshold crossing history but does not materially expand on parameter semantics beyond what the schema already provides.

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 states a specific verb ('Get'), a clear resource (substantial shareholders for an NZX company), and precise scope (5%+ voting rights from NZX disclosure notices). It also distinguishes itself from the closely related get_shareholders by noting the difference between legally mandated real-time disclosures and top-20 annual report data.

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 description provides explicit use cases (block holder analysis, activist investor tracking, M&A signal detection, ownership concentration analysis) and names get_shareholders as a complementary alternative. It clearly positions this tool as the real-time disclosure source versus annual report data, though it does not state an explicit 'when not to use' condition.

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