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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so safety is covered. The description adds genuinely useful behavioral detail beyond that: the granular balance breakdown (allowance/used/pending/booked ahead/remaining), the inclusion of notice and approval rules, and that request ids are returned. It does not discuss pagination or result size limits.

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, front-loaded with the core action and scope, then a user-intent mapping. The middle enumeration of balance fields is dense and slightly list-like, but every element corresponds to a distinct piece of returned data rather than filler.

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 read-only list tool with an output schema present, the description needn't explain return formatting, and it still supplies scope, data groups, and intent examples. An agent has everything required to select and invoke it 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 userId parameter is fully documented in the schema itself, including when it is unnecessary and that other IDs are refused. The description adds nothing about the parameter, so baseline 3 applies.

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 (reads) and a precisely scoped resource (the signed-in person's OWN time off), then enumerates the three data groups returned: balances per leave type, workspace leave types with notice/approval rules, and upcoming/pending requests with ids. The 'own'/'signed-in person' framing clearly distinguishes it from siblings like list_pto_requests and list_time_entries.

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 closing sentence maps real user intents ("how much vacation do I have left?", "what time off have I booked?") to this tool, which gives an agent clear usage context. It stops short of naming exclusions or pointing to alternatives such as list_pto_requests or request_time_off, so it is clear context rather than explicit routing.

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