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

Annotations already declare readOnly, idempotent, open-world and non-destructive, so the safety profile is covered. The description adds genuinely new context: it is a live/current answer that changes after reshuffles, it comes from the Members API, it costs 1 credit, and it enumerates the exact post families included. Only the return-shape/pagination behavior is unstated.

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 what it returns and the PM-first ordering, then the use case, then the filter, then coverage limits and cost. Dense but every clause carries information; the long parenthetical enumerating included posts is the only mildly padded segment, though it usefully draws the boundary.

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?

There is no output schema, and the description compensates by listing the exact returned fields and their ordering (Prime Minister first). Combined with the coverage boundary, credit cost and filter semantics, an agent has everything needed to decide to call it and to interpret the result.

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 the single optional parameter already documents the 2-100 character filter and an example. The description restates the same semantics ('filters by post, department or name') without adding matching behavior, partial-match rules, or default behavior beyond 'default all posts', which is also in the 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 verb-and-resource pair: current holders of UK Cabinet and Cabinet-level posts, with a fixed field list (post, department, minister, party, seat, start date) and the data source (UK Parliament Members API). It is clearly separable from siblings like mp_lookup or member_career_history because it is a point-in-time snapshot of executive officeholders, not MP or career data.

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 an explicit trigger ('who is the current Chancellor / Health Secretary?' after reshuffles) and an explicit coverage boundary: ~28 Cabinet and Cabinet-level posts, with junior ministers, most Ministers of State and Parliamentary Under-Secretaries excluded. It does not name an alternative tool for the excluded cases, so the agent must infer where to go for junior ministers.

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