Create a plan

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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false and openWorldHint=false, so the mutation profile is covered. The description adds conceptual context about recurring billing but says nothing about prerequisites, whether a plan can be modified afterward (update_plan exists), or what the response contains. Note the schema offers an idempotency_key even though idempotentHint=false, which is a nuance the description does not clarify.

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?

Short overall, but the first sentence 'Create a plan.' is pure repetition of the title and the second sentence restarts with the same phrase. The substantive content (billing period formula, subscription hand-off) is good, but one sentence is wasted.

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 7-parameter mutation with no output schema, the description covers the core concept and the natural next step adequately; return shape is unspecified but the plan object model is at least implied. Slightly incomplete on idempotency behavior and post-creation editability, but nothing critical is missing for a correct call.

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 43%, so the description should compensate. It does add real meaning for the compound `interval_count` × `interval` billing period, the trickiest parameter pairing, but it leaves name, description, metadata and idempotency_key unaddressed (amount's kobo unit is covered only by 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 and resource plus the domain meaning: 'an amount billed every `interval_count` × `interval` (for example every 3 months)'. That clarifies what a plan actually is, and it names the downstream consumer (create_subscription via POST /api/v1/subscriptions), so an agent can separate it from subscription creation. The only weakness is the redundant restatement of 'Create a plan' twice.

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 gives a follow-up path ('Subscribe customers to it with POST /api/v1/subscriptions'), which implies the tool is a prerequisite for subscriptions, but there is no explicit when-to-use/when-not guidance versus siblings like create_subscription or update_plan. Usage is inferable rather than stated.

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