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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, and closed-world, so the safety profile is covered. The description's added detail (previous vs current percentage, share counts, holder type, disclosure dates) largely duplicates the output schema rather than revealing operational behavior like auth needs or rate limits, so the added value is moderate.

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?

Three tight sentences, front-loaded with the resource being fetched, then the event categories, then the use cases. No filler, though the field list in sentence three is somewhat enumerative.

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, return-value detail need not be spelled out, and annotations cover the safety profile, so the description is broadly complete for invocation. It could still better route the agent relative to the many nearby ownership tools, but nothing essential 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 the schema already documents ticker, days, and type. The description echoes the change-type categories (increases, decreases, initial, ceased) that map to the 'type' filter but adds no format or default guidance beyond the schema, making the 3 baseline 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?

States a specific verb and resource ('Get substantial holder ownership change events') scoped to NZX companies, and the 'change events' framing implicitly distinguishes it from current-holder siblings like get_substantial_holders. However, it never names a sibling to make the distinction explicit, so it falls short of the top tier.

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?

'Use for monitoring institutional ownership shifts, activist accumulation, and divestment patterns' gives clear situational context for when to reach for this tool. It offers no explicit exclusions or named alternatives (e.g. when to prefer get_substantial_holders or get_substantial_holder_notices), so it stops 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.