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

Annotations already establish readOnly, idempotent, closed-world, non-destructive behavior, so the bar is lower. The description adds genuinely new behavioral detail not in any structured field: the exact set of returned values and the hard cap of the most recent 10 transactions. It omits what happens on an unknown member_id, which keeps it from a 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?

Two sentences, front-loaded with the action and then the return payload; the parenthetical example illustrates grounding value rather than restating the schema. The quoted example costs a few words but earns them by showing intended use.

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, describing the return shape is the right call and it does so well, capping transactions at 10. However, for a two-required-parameter tool it leaves agent_session_id unexplained and says nothing about failure behavior for an unknown or unenrolled member, so the definition is not fully self-sufficient.

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%, so the description must carry parameter meaning, but it only glosses member_id and never mentions agent_session_id, a required parameter. Neither parameter gets format, provenance, or sourcing guidance (e.g., where the session id comes from).

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?

The description uses a concrete verb and resource ("Look up a loyalty member by member_id") and enumerates what comes back (balance, tier, lifetime_points, recent transactions), so an agent knows exactly what this tool produces. It stops short of naming the sibling it complements (join_loyalty) or excluding it, but the read-only lookup nature is unmistakable.

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?

Usage is only implied via "so the agent can ground its recommendation", which gives a hint about the conversational context but no explicit when-to-use or when-not-to-use rule. It never says what to do when the member is not enrolled, which is exactly when join_loyalty would be the alternative.

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