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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, and the description goes beyond them by enumerating exactly what comes back: countries covered, networks, policies, provider page, buy link, and price history. It doesn't mention rate limits, error behavior for stale ids, or depth of the price history, so it's strong but not exhaustive.

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?

One front-loaded sentence with no filler — the purpose comes first and the return-contents list follows. The list of fields is dense and unprioritized, but every clause carries information.

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?

Since there is no output schema, enumerating returned fields (coverage, networks, policies, buy link, price history) is exactly the missing information and it's supplied here. Remaining gaps — unknown-id behavior and how much price history is returned — are minor for a simple read-only lookup.

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?

With one parameter at 100% schema coverage, the schema already carries type and example format; the description adds the meaningful semantic that the id comes from a prior search_plans call, telling the agent how to obtain a valid value rather than guessing.

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 resource and scope: 'everything esimdata knows about one plan' keyed by an id, and explicitly attributes that id to search_plans, which separates it from the sibling list/search tools. A slight gap is that the retrieval verb itself is implicit rather than stated.

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 parenthetical '(by the id search_plans returned)' implies the chained workflow — call search_plans first, then fetch with this tool — which is real, actionable guidance. However, it never states when NOT to use it (e.g., use compare_plans or country_overview instead) or what happens with an unknown id.

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