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

Annotations already cover readOnly/idempotent/non-destructive, so the safety profile is settled. The description adds value beyond that by disclosing the return payload (balance, tier, lifetime_points, last 10 transactions), which matters because there is no output 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?

Back-loaded with the key return-field list and one illustrative example; the quoted sample message adds a little flavor but the core content is front-loaded and tight.

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?

With no output schema, the description usefully enumerates what comes back, which is the main completeness concern. The only real hole is the undocumented agent_session_id and the absence of any not-found/error behavior.

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 0% and the description only glosses member_id, leaving agent_session_id completely unexplained in both schema and prose. For a 2-param tool with no structured documentation, the description does not compensate for the gap.

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?

Specific verb+resource ('Look up a loyalty member by member_id') and it enumerates the returned fields, which cleanly separates it from write-side siblings like join_loyalty and apply_promo.

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?

It gives a rationale ('so the agent can ground its recommendation'), which implies the context of use, but never states when to prefer this over join_loyalty or apply_promo, nor any prerequisites such as an existing membership.

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