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 profile is fully covered. The description adds which attributes are compared (fees, ratings, tax benefit, minimums, eligibility), which is useful context about output content, but says nothing about return format or how missing/invalid plan slugs are handled.

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?

A single well-formed sentence that front-loads the verb and resource, then lists the differentiating comparison dimensions. No filler, no redundancy.

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 one-parameter read-only tool whose annotations cover safety and whose only parameter is fully described in the schema, the description covers scope and compared attributes adequately. It could be tighter by noting the output shape, but nothing critical for correct invocation 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 description coverage is 100% and the input schema already documents the single parameter ('Plan slugs or names' with minItems 2 / maxItems 4). The description's 'two to four' simply restates those schema constraints, adding no new semantic detail such as slug format or ambiguity resolution between names and slugs.

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 (compare), resource (529 plans), cardinality (two to four), and the comparison dimensions (fees, ratings, tax benefit, minimums, eligibility). The comparison framing clearly distinguishes it from siblings like get_529_plan (single plan) and list_529_plans (enumerate).

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 by the verb: call this when you want plans side by side. However, it names no alternatives (get_529_plan / list_529_plans) and gives no guidance on when a single-plan lookup would be preferable to a comparison, so the agent must infer the routing.

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