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

Annotations already declare readOnlyHint=true, so the safe-read profile is covered. The description adds useful field-level context about what is returned and cites the underlying endpoint, but says nothing about error behavior (e.g., invalid/unknown memberId) or any permission scoping.

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 sentence with zero waste, front-loading the action and resource before the returned fields. The endpoint citation is compact supplementary information rather than filler.

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 read-only lookup with one fully documented parameter and readOnlyHint annotations, the description covers purpose and return shape adequately even without an output schema. Only minor gaps remain around error handling and authorization scope.

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% for the single memberId parameter, so the schema already carries the semantics. The description's 'by id' merely reinforces that memberId is the identifying key without adding format or constraint details.

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 ('Fetch one customer by id') and enumerates the returned data (contact details, first/last seen, visit counts, custom fields, tags). 'By id' implicitly distinguishes it from the sibling list_members, though no sibling is named explicitly.

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 'by id' phrasing implies single-record lookup, but there is no explicit guidance on when to use this versus list_members or get_current_user, and no prerequisites or exclusions are stated. Usage is inferable rather than stated.

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