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

Annotations already declare readOnly/not-destructive/open-world, so the safety profile is covered. The description then adds genuinely non-annotation behavior: it returns exactly one page, uses keyset paging, and the next_cursor from the prior reply must be passed as start_cursor — actionable context an agent cannot get from the annotations.

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 compact sentences, resource and scope front-loaded, then endpoint and paging caveat. No filler text; arguably the 'GET /labels' fragment adds little for an agent but costs only three tokens.

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 zero-required-param list tool with full schema coverage, safe annotations and no output schema, the description covers what the agent needs: what is listed, paging mechanics, and the cursor handoff. Return item fields are not described, but paging behavior is the main risk here and it is addressed.

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 100%, so the schema already documents name, sort_by, per_page, start_cursor and sort_direction, making 3 the baseline. The description's only added parameter meaning is the next_cursor→start_cursor handoff, which the start_cursor schema description already states, so it adds little beyond duplication.

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 resource (labels/tags) and scopes it to the entity types it applies to (vehicles, issues, work orders, service entries), plus the endpoint GET /labels. It is distinguishable from siblings like fleetio_list_groups or fleetio_list_vehicle_statuses, though the leading word 'Lookup' slightly understates that this is a paginated list operation.

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?

No explicit when-to-use or when-not-to-use guidance and no named alternative among the ~40 sibling list tools. The cross-entity scope note ('used on vehicles, issues, work orders and service entries') implies the agent should call this when it needs the shared tag vocabulary, which is weak but non-zero guidance.

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