nonprofit_fetch_charity_uk

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

The description discloses that the tool returns income, activities, and registration details, giving basic expectations. However, with no annotations, it lacks information on error handling, authentication needs, or rate limits. The output schema exists but is not described further.

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 three sentences, front-loaded with the action, then input guidance, then output summary. Every sentence contributes value without redundancy or fluff.

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 simple lookup tool with one parameter and an output schema, the description covers the purpose, input, and output. It could hint at what happens if multiple charities match a name, but overall it is sufficiently complete for an agent to use 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?

The input schema has 0% description coverage, so the description compensates by explaining that the parameter 'charity_number_or_name' can be either a charity number or organisation name. This adds essential meaning beyond the raw 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?

The description clearly states the tool is for looking up a UK registered charity by number or name. It specifies the verb 'look up' and resource 'UK registered charity', and distinguishes from sibling tools like nonprofit_fetch_nonprofit_by_ein (US) and nonprofit_search_nonprofits_by_name (search).

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 clear context: 'Use this to look up a UK registered charity by number or name.' It implies this tool is for specific lookups by identifier, not for broad searches. However, it does not explicitly state when not to use it or mention alternatives, though sibling tools serve different jurisdictions.

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