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, covering the safety profile. The description adds meaningful behavioral context beyond that: it enumerates the returned fields and discloses the specific error condition (PLAN_NOT_FOUND). It stops short of mentioning permissions or rate limits, so it is useful 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?

The description is front-loaded with purpose and immediately follows with return shape, alternatives, and error behavior. Every sentence earns its place by adding distinct value: lookup scope, return contents, sibling routing, and failure mode. There is no filler or repetition.

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?

Given there is no output schema, the description appropriately describes the return fields in detail (key, name, prices, quotas, etc.). Combined with the explicit sibling alternatives and error condition, an agent has enough context to invoke this read tool correctly. The 100% schema coverage for parameters and the read-only annotations mean nothing essential 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%, so both parameters are already documented in the schema, including the example 'pro' for key and the app fallback behavior. The description restates the key example but adds no new syntactic or semantic detail beyond what the schema provides. A score of 3 is the correct baseline when the schema does the heavy lifting.

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 opens with a precise verb and resource: 'Read one subscription plan by its KEY'. It states the exact lookup scope and what is included (prices and per-metric usage quotas), which distinguishes it from list_plans and get_stripe_status. An agent can identify the operation and its target without opening the 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?

It names specific alternatives and the conditions that select them: list_plans to discover keys, list_plan_quotas when only the quota array is needed, and get_stripe_status to verify billing wiring. The failure condition PLAN_NOT_FOUND further clarifies behavior. This is explicit when-to-use guidance with no guesswork.

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