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

Annotations already declare the safety profile (not read-only, idempotent, non-destructive). The description adds a genuinely useful behavioral trait beyond them: all-or-nothing semantics when any message is missing. However it omits whether add/remove labels are merged or replaced and how conflicting labels are handled.

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 tight sentences with no waste; the scope limit leads and the atomicity caveat follows immediately. Everything earns its place.

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?

An output schema exists so return values need no explanation, and annotations cover safety. But for a 3-param mutation with 0% schema coverage, the description leaves add/remove semantics and sibling-tool selection unaddressed.

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 carries the burden, yet it never distinguishes add_labels from remove_labels or explains that message_ids is required and uuid-formatted. 'The same label changes' is vague about the add/remove mechanics.

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 (apply label changes to received messages) and adds a concrete scope bound (up to 100). The word 'received' implicitly distinguishes it from bulk_update_sent_message_labels, though no sibling is named explicitly.

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 'bulk' framing and the 100-message cap imply this is for multi-message operations, but there is no explicit guidance on when to choose this over update_message_labels (single) or bulk_update_sent_message_labels. Usage is inferable but not stated.

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