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

Annotations already declare read-only, idempotent, non-destructive, so safety is covered. Beyond that the description discloses the tri-state result (yes / no / not published), the per-plan fields returned (name, validity, price in USD), a summary line format, and the ordering rule 'own page first, then regional plans' — substantive behavior with no output schema to carry it.

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?

Front-loaded with the core action, then the nuance, then the output shape and the alternate mode. Three sentences, all load-bearing. The rhetorical example question is slightly padded but is the fastest way to convey the regional-plan trap.

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?

No output schema exists, yet the description specifies exactly what comes back per plan and in aggregate, plus the fallback mode's ordering. For a 3-parameter read tool with full annotation coverage, nothing an agent needs to select or call it correctly is missing.

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 100%, so baseline is 3. The description still adds real meaning for the optional destination parameter: it changes the query direction entirely (list every destination containing the country, ranked own page first), and it clarifies that the country input is validated against real plan coverage rather than destination membership.

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: check whether a country is covered, plan by plan. The Europe/France/Turkey example and the 'destination's country list is not every plan's coverage' line make it unmistakably distinct from search_plans or get_plan, which the agent would otherwise confuse with a coverage query.

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?

Gives clear usage context: use it to check whether a specific country is on a specific plan's coverage list, and explains the reverse mode (omit destination to find all destinations including the country). It also warns why this differs from reading a destination page. It does not explicitly name which sibling to use instead, so it falls short of a full when/when-not/alternative rubric.

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