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

Annotations already cover read-only, idempotent, closed-world and non-destructive, so the description earns credit for what it adds: 'Costs 1 call' discloses a quota/rate-limit consideration, and it states that directory listings carry an as_of date. It stops short of saying what happens when the plan ID is unknown (empty result vs. error), which is the one behavioral gap an agent would care about.

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, front-loaded with the identifier and scope, with no filler. The long mid-sentence enumeration of returned fields is the weakest part, since an output schema already exists and makes that listing largely redundant.

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?

With only two parameters at full schema coverage, rich annotations, and an output schema carrying the return shape, the description supplies everything still missing: which plan families are supported and the per-call cost. Nothing an agent needs in order to invoke this correctly is absent.

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% and the schema itself carries the detailed ID formats (14-char ACA, H1234-001-000 MA) and the default-all-years behavior of 'year'. The description only restates that lookup is by plan ID and repeats the two plan families, adding no semantics beyond the schema. 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?

The description states a specific verb and resource ('Details of one ... plan by plan ID') and scopes it to a single record, which is clearly distinct from batch/lookup siblings like check_network_batch or lookup_provider. It never explicitly contrasts itself with siblings such as coverage or plans_for_provider, so an agent must infer the boundary from the singular 'one plan by plan ID' framing.

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 only implied: 'by plan ID' signals this is the retrieval step once an ID is known, and the two plan families named tell the agent both are accepted. There is no explicit when-to-use, no when-not, and no pointer to which sibling to call first to obtain a plan ID.

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