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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety and repeatability profile is fully covered. The description adds the payload contents (inclusions, current promotion terms, detail-page link), but since an output schema exists this is partly redundant rather than new behavioral insight.

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, no filler: the first front-loads what is returned and its identifying inputs, the second gives the prerequisite. Nothing in the text is padding.

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 3-required-param read tool with an output schema and full annotation coverage, the description supplies the identity inputs, the dependency chain for obtaining slugs, and a rough sense of the response. Only the plan_type enum semantics remain unaddressed in prose.

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 0%, but the description names all three required parameters and frames them as a composite lookup key, which compensates partially. It does not explain the allowed plan_type values (mobile, prepaid, mobile_broadband, internet) or the slug format constraints, leaving that to the enum and pattern in 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 (return details) and resource (one plan) plus the exact identifying keys (plan type, provider slug, plan slug) and the payload (inclusions, promotion terms, detail link). An agent can distinguish it from search_plans, compare_plans and list_providers without opening any schema.

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 tells the agent where the required slugs come from — 'Use the slugs returned by search_plans or list_providers' — which is the key prerequisite for calling this tool. It does not, however, state when to prefer this over compare_plans for multi-plan evaluation, so the routing is clear but not exhaustive.

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