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

Annotations declare readOnlyHint=true and destructiveHint=false, and the description adds no contradiction. It enriches this with zero-cost invocation, callable at balance=0, and the specific account state fields returned, which is useful behavioral context beyond 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?

The description is well-structured with labeled sections and every line carries operational information: returns, use cases, exclusions, path fit, and cost. It is thorough without redundancy.

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 no-parameter, read-only tool with an existing output schema and clear annotations, the description covers when to use it, what it returns, cost behavior, and availability. No material gaps remain.

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?

There are zero parameters, so there is nothing for the description to explain beyond the empty schema. The baseline of 4 applies because the schema fully covers the parameter surface.

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 opens with a specific verb ('Return') and enumerates the exact outputs: account_id, IU balance, USD equivalent, frozen flag, and recent ledger entries. This clearly distinguishes it from sibling billing tools and the inline `_cost` envelope.

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?

Explicit 'Use when' and 'Do not use when' sections specify the intended scenarios (checking credit before large batch, debugging charges) and explicitly advise against using it for per-call cost, directing to the `_cost` envelope. It also clarifies the MCP-only path fit.

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