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

Annotations show this is a mutating, non-idempotent operation, and the description adds genuinely useful behavioral detail by revealing the two-step behavior: omitting confirm returns a preview with package name, cost, and balance, while confirm=true executes. It doesn't cover post-execution details, but it adds meaningful context beyond 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?

The description is compact and front-loaded: one sentence defines the core action, and the next sentence conveys the two-step mechanics with no filler or redundant restatement.

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 three-parameter tool with full schema coverage and no output schema, the description covers the essential usage flow and the preview return. It omits what the execution step returns and doesn't explicitly point to get_topup_packages in the description, but the schema covers that dependency, so the context is largely complete.

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 baseline is already 3. The description goes slightly beyond the schema by explaining the behavioral difference between omitting confirm and passing true, which adds semantic value for the confirm parameter beyond the schema text.

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 action ('Add a package to an existing eSIM') and the title adds 'spends balance,' which distinguishes it from activation, cancellation, or suspension. It doesn't explicitly name a sibling alternative, so it stops short of a 5.

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 description implies when to use it: to add a package to an existing eSIM, and the two-step flow is explained. However, it never explicitly contrasts it with siblings like get_topup_packages or create_order, so usage guidance is largely implicit.

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