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

With no annotations provided, the description carries full behavioral burden. It effectively discloses that the tool has no parameters (empty input_schema), is a read-only informational listing, and produces slugs for a specific purpose. It does not describe the output format or any potential caching behavior, but the simplicity of the tool (0 params) makes this less critical.

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?

Two sentences, no wasted verbiage. The first sentence states the core function, the second provides critical usage guidance. Every word earns its place. Perfectly 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?

Given 0 parameters, no annotations, no output schema, and a simple listing function, the description is nearly complete. The only minor gap is not mentioning whether the list includes all possible destinations or if there are any prerequisites/caching. However, for a straightforward list tool, this is adequate.

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?

The input schema has 0 parameters and 100% coverage, so the baseline is 4. The description adds value by explaining how the output (slugs) relates to sibling tool input, which is beyond what the empty schema provides. No need for param documentation since none exist.

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 states the tool lists Alt eSIM destinations including country/region slugs, English names, and region. It distinguishes itself from siblings by explicitly mentioning the output includes slugs that are used as input for search_esim_plans. The verb 'list' is specific and the resource 'Alt eSIM destinations' is well-defined.

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 explicitly tells the agent when to use this tool (to find slugs for search_esim_plans), providing a direct connection to a sibling tool. It lacks explicit 'when not to use' guidance, but the context of usage is clear and actionable.

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