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

Annotations already declare readOnlyHint=true and openWorldHint=true. The description adds useful behavioral detail beyond the annotations: a leave type that does not apply to the employee returns error text rather than a balance.

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?

The definition is two focused sentences with no wasted text. The core purpose and optional scoping behavior are front-loaded, and the error behavior is appended efficiently.

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 simple read-only balance lookup with full schema coverage and safety annotations, the description gives enough context to invoke it correctly. It is slightly incomplete because there is no output schema and the description does not describe the returned balance fields or structure beyond 'balance' and 'error text'.

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 all three parameters are already documented in the schema. The description reinforces that query_date sets the computation date and leave_type_id optionally restricts results to one type, but adds little syntax or format 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?

The description states a specific verb and resource: getting an employee's leave balance on a date, optionally narrowed to one leave type. It is clear, but it does not explicitly distinguish this tool from nearby siblings such as get_off_in_lieu_balance or get_leave_entitlement_period.

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?

It implies usage by explaining that the tool returns every leave type unless leave_type_id is supplied. However, it gives no explicit guidance on when to choose this instead of related leave or entitlement tools, and it names no alternatives.

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