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

Beyond the annotations, the description discloses genuinely useful behavior: the tool performs no lookup, returns an instruction instead of an action, and is deliberately non-disclosing about existing enrolments. That privacy/scope constraint is exactly the kind of context annotations (readOnlyHint=false, idempotentHint=false) cannot convey, and nothing in the text contradicts them.

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 dense sentences, and the most decision-relevant caveat (joining happens on the menu, this tool only answers with that instruction) is front-loaded. Slightly compressed but nothing is wasted.

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 correctly carries the return-value burden by stating the tool 'answers with that instruction'. Combined with the session prerequisite and no-lookup guarantee, an agent has enough to call it correctly; only the explicit alternative (check_loyalty) is unstated.

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% and the schema already states that email, phone and display_name are not used and that agent_session_id is an active session id. The description only repeats the session requirement, adding no syntax, format, or fallback detail beyond the schema. Baseline 3 applies.

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 states a specific verb+resource (loyalty sign-up for a guest) and immediately explains the counterintuitive truth that no sign-up actually occurs here. It implicitly separates itself from check_loyalty by noting it 'never reveals whether an e-mail or phone is already enrolled', though it never names that sibling outright.

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 clear context: the guest must confirm their own e-mail, so enrolment happens on the restaurant's menu, and this tool exists to return that instruction. The prerequisite ('Requires an active agent_session_id') is stated. It stops short of explicitly routing enrollment-status questions to check_loyalty.

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