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

Adds substantial behavior beyond the annotations: the tool is always proposed, returns status='confirmation_required' with action_id and plan_token, and only writes after confirm_action — none of which is in the annotation block. The only soft spot is the claim that labelling 'changes nothing on the mail server' sitting next to destructiveHint=true, which could lead an agent to under-estimate side effects; it stops short of a direct contradiction because the write path is acknowledged.

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?

Front-loaded with the action, then provenance, then an explicit 'CONFIRMATION:' marker for the two-phase flow — an agent scanning it can find the critical constraint instantly. Slightly long for two parameters, but every clause carries information.

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 tool with no output schema and no parameter documentation, the description covers purpose, input provenance, and the mandatory confirmation round-trip, which is what an agent most needs. It omits the batch-size cap and add-vs-replace semantics, minor gaps given the confirmation step lets a human review the plan.

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 compensate: it explains where each of the two parameters comes from, which is genuinely useful provenance. However, it says nothing about the 1–50 item limit, whether message_ids may be strings or integers, or whether labelling replaces or adds to existing labels.

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 ('Put a label on messages') and immediately disambiguates by naming the source of each input — message ids from mail_list_messages, label_id from mail_list_labels — which separates it from mail_create_label and mail_list_labels without opening a schema.

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?

Gives clear preconditions (you must have ids from mail_list_messages and a label_id from mail_list_labels) and clarifies the operation is local filing, not a server-side change. It stops short of explicit when-not-to-use guidance or naming a true alternative such as mail_move or mail_set_flag.

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