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

Annotations already declare readOnly, idempotent, non-destructive, open-world, so the safety profile is covered. The description adds genuinely new behavioral context: the authoritative data source, the 1-credit cost, and the caveat that former members typically return empty details. It does not cover error behavior or empty-result shape, keeping it below 5.

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?

Three front-loaded sentences: what it returns, who it is for, what it needs and its caveat, plus a cost tag. Dense and useful, with only minor redundancy against the schema's parameter note about mp_lookup/constituency_search.

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 single-parameter, read-only lookup with no output schema, the description fully covers what an agent needs: the field list returned, the prerequisite id source, the empty-result caveat, and the credit cost. Nothing material is missing.

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 parameter already documents itself, including the example value 172 and its derivation from mp_lookup or constituency_search. The description's mention of needing a member id largely restates the schema, so it earns the baseline 3 rather than more.

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 (official contact details for an MP or peer) and enumerates exactly what is returned: parliamentary and constituency office addresses, phones, email, website, listed social media. It also names the upstream source (UK Parliament Members API), so the agent can distinguish it from siblings like mp_lookup, member_career_history, or member_registered_interests.

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 ("how do I contact my MP?" for letter writers and constituents with casework) and an explicit prerequisite chain: the member id comes from mp_lookup or constituency_search. It also warns that former members usually have no details listed, which is an implicit when-not. No sibling is explicitly excluded, so it stops short of a 5.

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