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

No annotations are supplied, so the description carries the full burden. It usefully discloses the cost ('1 credit') and that this is a read of register data, but says nothing about behavior for an unknown/non-registered number, whether financial figures are per financial year, currency, or rate limits.

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?

A single front-loaded sentence delivering the source register, the identifier, the returned fields, and the cost. Nothing is padded or redundant.

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 one parameter, no output schema and no annotations, the description does the heavy lifting well by listing the fields returned. It falls short only on input format and error behavior for invalid charity numbers.

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%, but the schema text is only 'string, required', so the description's 'registered charity number' does add the meaning of the single parameter. However, it gives no format guidance (e.g. numeric string, digits only), so it does not fully compensate for the thin schema.

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 resource ('Charity Commission register details') keyed by a specific identifier ('registered charity number') and enumerates the returned fields (status, income, expenditure, activities, address). No sibling tool covers charities, so differentiation is moot, but an agent instantly knows what this does.

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?

Offers no explicit when-to-use or when-not-to-use guidance, no note on where to obtain a registered charity number, and no mention of related tools (e.g. company_search for non-charity entities). Usage is only inferable from the phrase 'for a registered charity number'.

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