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

Annotations already declare readOnlyHint, idempotentHint and non-destructive behavior, so the bar is lower. The description still adds real value beyond them: the England-and-Wales jurisdiction and an explicit per-call cost of 1 credit, which matters for planning repeated searches. It does not explain how closed/removed charities affect results, leaving that to the schema.

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?

Two sentences, both front-loaded with the core action and the decision-driving use case. The cost note is compact and placed at the end where it does not bury the main purpose. No filler wording.

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 three-parameter read tool with no output schema, the description covers jurisdiction, purpose, returned fields and cost. The one material omission is sibling routing among charity_search, charity_lookup and charity_profile, which an agent would need to choose 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?

Schema description coverage is 100%, so name, limit and includeRemoved are already documented in structured form, making 3 the baseline. The description confirms name-based lookup but adds no meaning about match semantics (exact vs partial), pagination, or what includeRemoved changes in the response.

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 (find a registered charity in England and Wales by name) plus the fields returned (charity number, status, registration date). It does not differentiate itself from the sibling tools charity_lookup and charity_profile, so an agent cannot tell from the description alone which one to pick.

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?

Gives a concrete use case — verifying a charity is real before donating, partnering or paying it — which implies when to reach for it. It offers no when-not conditions and never names charity_lookup or charity_profile as alternatives for looking up by number or fetching deeper details.

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