List labels

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the bar is lower, yet the description adds real content: which label categories are returned, the fields per label, and the sort order. It does not discuss volume, pagination, or what happens on an unknown/unconnected account, and restates "Read-only" redundantly.

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: identity of the tool first, then the two routing use cases, then an availability note. The trailing "Read-only" earns little since annotation readOnlyHint already says it, but overall there is no wasted bulk.

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-param, read-only list tool with no output schema, the description covers content, fields, ordering, and downstream usage, which is everything an agent needs to call it and consume the result correctly.

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% and the single optional account parameter is fully documented there, so the description adds no meaning about it beyond referencing "one mailbox" implicitly. Baseline 3 is appropriate when the schema carries the parameter semantics.

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 ("List every label of one mailbox") and scopes it precisely: system labels plus user labels, each with id, name and type, sorted by name. It is clearly distinguishable from siblings create_label and modify_labels, which mutate the same resource.

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 two concrete when-to-use paths: finding the exact name for a "label:" search in search_emails, or the name/id to pass to modify_labels. It also preempts an availability question with "Works on every account, with or without --labels."

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