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

Annotations already declare idempotentHint=true and destructiveHint=false, but the description adds genuinely new behavior: the tool is get-or-create, returning an existing live list when the name matches rather than failing. It also explains the concrete retry protocol (reuse the same idempotency_key), though it omits what the response contains and any permission requirements.

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 short sentences with the primary action front-loaded and no filler. The phrase "answers the live one with that name" is awkwardly worded for get-or-create semantics, costing a point on clarity but not length.

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 two-parameter mutation with no output schema, the description covers creation, deduplication, and retry, but never says what comes back (an id? the list object?), which an agent needs since it must pass that list into edit_contacts. The absence of an output schema makes that omission more consequential.

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 50%: idempotency_key is fully documented in the schema, while name has no description at all. The description partially compensates by implying name is a matching key against existing lists and by restating the retry rule for idempotency_key, but adds nothing on name normalization, case sensitivity, or the maxLength constraint.

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?

Names a specific verb and resource ("Makes a contact list") and adds scope ("on the Contacts page"), so the agent knows exactly what is created. It does not explicitly contrast itself with the sibling edit_contact_list, which is the nearest alternative, so it falls short of full sibling differentiation.

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 description routes one adjacent task to a sibling ("Add people to it with edit_contacts (op add_to_list)"), which is useful when-to-use guidance for follow-on work. It never states when to use this versus edit_contact_list, nor what happens if the name already exists beyond the vague "answers the live one with that name".

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