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

Annotations already declare a safe, idempotent, read-only, closed-world operation, yet the description adds substantial context beyond them: validity start rules for data vs number plans, install-timing warnings, the French +33 number for Europe, the UK after-arrival constraint, regional fallback behavior, and final USD pricing with crypto set at create_order.

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 front-loaded with the core purpose and ordering, then layers useful warnings. It runs several dense sentences, but nearly every clause carries decision-relevant information such as install timing and regional fallback.

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 no output schema, the description covers purpose, type semantics, fallback behavior, and pricing. It does not describe the return shape or pagination, which is a minor gap but not critical for correct invocation.

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%, so baseline is 3, but the description meaningfully expands the type parameter beyond its brief schema description by explaining validity start, phone/SMS capability, and regional number formats. It says less about include_regional and destination, so it does not fully saturate all three parameters.

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 ('List purchasable plans for a destination') and adds a distinguishing ordering guarantee ('cheapest first'). An agent can tell this apart from the singular get_plan sibling without opening either schema.

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 explains how to choose the plan type and references create_order for crypto pricing, which implies an ordering workflow. However, it never explicitly says when to use this tool versus siblings like get_plan or search_destinations, so usage is implied rather than directed.

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