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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open world), so the bar is lower. The description adds genuinely useful non-schema context: the data source authority and the BYO API-key requirement, including that Pipeworx does not front a key and a call without one is refused. It omits pagination/limits for large trustee lists.

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 purpose, then usage, then the auth constraint, then a concrete example call — a logical order with little waste. Slightly dense (three long sentences plus example) but every element carries information.

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 only three parameters and full schema coverage, the description still describes return contents and the blocking auth requirement, which is what an agent most needs. It does not address result paging or error cases, but there is no output schema to offload that to, so those are minor gaps.

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 baseline is 3. The description's parameter-level content (charity_number example, the _apiKey BYO requirement and registration link) largely restates what the schema already documents, adding little meaning beyond it.

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 gives a specific verb and resource — 'List the named trustees of one UK registered charity' — and even annotates the return fields (id, appointment date, other trusteeships). It clearly reads as distinct from ukcharity_details / ukcharity_financials / ukcharity_search by resource, but it never names those siblings to explicitly route the agent.

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?

It provides concrete usage contexts with example questions ('who runs charity X', 'what else does this trustee sit on'), which is stronger than implied usage. It does not, however, state when NOT to use it or name the sibling tools to use instead for financials or general details.

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