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

The description adds the specific constraint that 'Funding does not authorize sending,' which is vital behavioral context not covered by annotations. The annotations already confirm it is safe (readOnlyHint: true, destructiveHint: false). Without these annotations, the description would need to carry the full burden.

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 extremely concise and efficient. Both clauses are necessary: defining the read operation and stating the critical business logic constraint.

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?

Given zero parameters and strong annotations confirming safety and idempotency, the description is complete. It covers the scope of the read operation and a critical business boundary. No additional information like output format is needed.

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?

Since there are 0 parameters (100% coverage), the baseline for parameter semantics is high. The description confirms that no specific parameters are required to read the balance.

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 clearly identifies the action ('Read settled USD service balance') and the resource being acted upon ('service balance'). While it doesn't use a strict sibling differentiation, the function of 'get_credit_balance' is obvious compared to siblings like 'create_credit_topup' or 'list_credit_transactions'.

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 provides a warning ('Funding does not authorize sending'), which acts as a constraint on usage. However, it doesn't specify *when* this is the right tool versus other balance inquiry methods, resulting in moderate guidance.

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