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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description still adds real value beyond that: it discloses that the output is a historical record plus an evaluative judgement, and that no forecasting is performed — a behavioral limit an agent would otherwise assume.

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 core purpose is front-loaded in the first clause, and the 'does not forecast' caveat is placed last where it belongs. The bilingual Korean restatement of the same content roughly doubles length without adding new information for an agent, which is a minor cost.

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, 3-parameter tool with no output schema, the description adequately conveys what comes back (daily history plus judgement). The remaining gap is that 'recent' is never quantified — the observation window length is unspecified — and the form parameter's effect is unaddressed.

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 67%; country and trip length are reflected in the description text, but the 'form' parameter (esim/usim) is never mentioned — and the description's phrasing 'cheapest unlimited eSIM price' arguably implies esim-only, when the schema accepts usim too. The days enum values and default are also left to the schema.

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+resource: returns a daily history of the cheapest unlimited eSIM price for a country and trip length, plus a cheapness judgement. That is clearly distinguishable from siblings like find_esim_prices or compare_countries, though the description never names or contrasts those siblings explicitly.

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?

Usage is implied (use it when you want the recent trend / a 'is now cheap?' judgement), and it adds one boundary — 'Does not forecast' — which tells the agent not to expect a prediction. However there is no explicit when-to-use-vs-alternative routing against find_esim_prices or compare_countries.

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