Get service countries

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

With no annotations, the description carries the full burden. It discloses the auth requirement ('No API key required'), the filtering behavior ('stock > 0'), and the fields returned. It doesn't mention rate limits, errors, or pagination, but for a simple list endpoint this is substantial behavioral context.

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?

Three concise sentences, each with a distinct purpose: the action and output fields, the auth note, and the follow-up usage. No filler, and the core function is front-loaded.

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 single-parameter tool with no output schema and no annotations, the description covers the essential calling contract: what it returns (including specific fields), that no API key is needed, and how to use the result for ordering. Pagination and error behavior are unstated, but those are secondary for this simple list operation.

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% – the schema already documents that slug accepts an SEO slug or service code. The description only echoes this in 'service code/slug' and adds no new parameter-level detail. Baseline 3 is appropriate when the schema already describes the parameter fully.

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?

Description leads with a specific verb and object: 'List in-stock countries for a service', immediately scoping the operation. It adds the filter 'stock > 0' and enumerates returned fields (prices, currency, stock, speed tiers), which distinguishes it from generic siblings like list_countries or get_service.

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 positions the tool as a prerequisite step: 'Use the returned isoCode + service code/slug to order a number.' This gives a clear context for when to call it. However, it does not explicitly name alternatives or state when not to use it, so it stops short of a 5.

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