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

Annotations already declare readOnlyHint=true, and the description adds meaningful operational context: it only needs gmail.readonly and requires no reconnect, it can span all accounts by default, and the returned ids are intended for label-modification siblings. It doesn't describe return shape, but it adds value beyond the annotation.

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 tight sentences front-loaded with the tool's scope, then prerequisite, then follow-up usage. Every sentence carries information an agent needs and nothing is padded.

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 one-optional-parameter, read-only list tool with annotations covering safety and no output schema, the description supplies scope, auth needs, cross-account default, and downstream usage. Nothing required to call it correctly 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?

There is only one optional parameter and schema coverage is 100%, so the schema already documents `accounts` fully. The description restates the subset-vs-all behavior but adds no syntax, format, or edge-case detail beyond the schema.

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 (list) and resource (Gmail labels), and scopes it precisely to system + user-created labels across all connected accounts. An agent can immediately distinguish this read tool from sibling mutators like create_label, update_label, and delete_label.

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?

Explains the default behavior (all connected accounts) and the alternative (subset via `accounts`), plus a prerequisite (gmail.readonly, no reconnect) and a follow-up use case (feed ids to modify_message_labels/modify_thread_labels). It lacks explicit when-not guidance, but the context is clear.

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