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

With no annotations, the description carries the full burden and does disclose meaningful behavior: no ordering occurs until email confirmation and no account is needed. However, it spends most of its words on the downstream purchase flow rather than on this call's own behavior (e.g. that it is a read-only lookup or what 'full details' encloses).

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 definition is front-loaded with the core purpose, which is good, but then devotes four sentences to the checkout, payment, and install journey that logically belongs to create_checkout_link. That detail is helpful user-facing context but not this tool's contract, diluting a description that should be tight.

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?

A read-only lookup with no output schema and no annotations needs the description to convey what comes back; 'full details' is vague and return fields are never hinted at. The auth-free nature ('No account needed') is covered, so the gap is moderate rather than severe.

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 both plan_id and the currency enum are already documented in the schema. The description only confirms the id's provenance ('from search_esim_plans') and adds nothing about the currency parameter, so the baseline 3 applies.

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 and resource ('Fetch full details of a single Siima eSIM plan'), scopes it to one plan by id, and names the sibling (search_esim_plans) that produces that id. An agent can confidently distinguish it from search_esim_plans and create_checkout_link.

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?

Explicitly routes the agent: the id comes from search_esim_plans, and buying is done via create_checkout_link, not this tool. It gives clear upstream/downstream context but stops short of stating when this tool should be skipped or contrasting it against list_destinations/list_regions.

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