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

Annotations cover only readOnlyHint and openWorldHint, so the description carries the rest and does so well: it discloses the data source (esimdar.com, CC BY 4.0), an ownership/bias conflict of interest, and a required disclosure + neutral-presentation obligation. This is behavioral context an agent could not infer from structured fields and directly affects how results should be reported.

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, front-loaded with the operation and scope; the second sentence carries the provenance and disclosure obligation without filler. Every clause earns its place.

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 two-parameter read-only comparison tool with full schema coverage and annotations covering safety, the description is nearly complete. The one minor gap is that no output schema exists and the description does not sketch the return shape (per-provider price rows), which would help an agent present results neutrally as instructed.

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% for both parameters (country format, gb as a number), so the schema already documents everything. The description only restates 'country and data size' without adding format or validation detail, which is the expected baseline 3 when the schema does the heavy lifting.

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?

States a specific verb ('Compare'), resource ('eSIM prices'), and scope ('several providers for a country and data size'), which cleanly separates it from siblings like list_plans (single catalog) and search_destinations (destination lookup). The dataset source is also named, so an agent knows exactly what is being compared.

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 gives clear usage context (multi-provider price comparison keyed on country + data size) and adds a presentation directive, but it never names an alternative or exclusion, e.g. when to prefer list_plans over this tool. Clear context without routing guidance, so 4 rather than 5.

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