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

Annotations already declare destructiveHint=true, and the description earns real credit by spelling out exactly what is destroyed: any label omitted from the payload is removed. That is materially more useful than the bare hint. One tension: 'sets the labels to exactly the list sent' describes idempotent behavior while idempotentHint is false, though this is an annotation-side issue rather than a descriptive contradiction.

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, zero redundancy, with the destructive replacement semantics front-loaded ahead of the practical keep-existing-labels tip. Nothing could be cut without losing decision-relevant 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, one-required tool with no output schema, the description covers the essential behavioral hazard. Minor gaps remain (what happens with unknown label names, whether labels must pre-exist via create_label), but nothing required for a correct call is missing.

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 100%, so the baseline is 3, but the description adds genuine meaning the schema lacks: the labels array is a complete desired set rather than an additive list, and it explains how to construct that payload. This is exactly the kind of semantics the schema's terse 'Array of labels' entry omits.

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 ('sets the labels of a contact') and immediately corrects the misleading 'Add' in the name by clarifying it is a full replacement, not an append. It does not explicitly name the sibling it differs from (conversation_add_labels, list_all_labels_of_a_contact), but an agent can still identify the operation precisely.

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 gives one concrete usage rule — resend existing labels to preserve them — which effectively implies a read-then-write workflow. However it never names the alternative tool for fetching current labels (list_all_labels_of_a_contact) or states when to prefer this over the conversation-level equivalent, so routing guidance remains implicit.

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