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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds useful provenance by naming NZX disclosure notices as the source, but the rest of the sentence enumerates return fields already captured by the output schema, so marginal behavioral value beyond structured data is modest.

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-loaded with the core definition, followed by field enumeration and use cases; three sentences, no fluff. The middle field list is somewhat redundant with the output schema and could be trimmed without loss.

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 the output schema exists and annotations are rich, the description is nearly complete: purpose, source, threshold, and analytical applications are all covered. The remaining gap is sibling disambiguation against the other substantial-holder and shareholder tools.

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 documented there, so baseline 3 applies. The description's mention of the 5% threshold gives implicit context for include_ceased, but it never explicitly explains that parameter's behavior or the expected ticker format.

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 (substantial shareholders, 5%+ voting rights, NZX disclosure notices) with a clear scope. However, it never distinguishes itself from near-identical siblings like get_substantial_holder_notices, get_substantial_holder_changes, or get_shareholders, leaving the agent to guess which to call for a snapshot versus a notice feed versus a change log.

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 final sentence names four concrete analytical use cases (block holder analysis, activist tracking, M&A accumulation signals, ownership concentration), which gives a strong positive signal for when to reach for this tool. It stops short of exclusions or naming an alternative when a different ownership view is needed.

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