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

With no annotations, the description carries the burden of disclosure. It states the action ('Create a checkout session') and the return value ('Returns a Stripe checkout URL'), which implies no immediate charge and a redirect flow. However, it doesn't mention potential prerequisites (e.g., authentication), side effects, or failure modes. This is acceptable but not rich.

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 three sentences, front-loaded with the primary action, then plan details, then return value. Every sentence adds necessary information without fluff or repetition. It is concise and well-structured.

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 subscription signup tool, the description covers the essential aspects: what it does, the plan options with prices, and the output (Stripe checkout URL). Since there is no output schema, this return-value info is crucial and provided. It could mention that no parameters are required (all optional), but that is inferable from the schema and not critical for invocation.

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?

The schema already covers all parameters with descriptions, and the tool description enhances this by mapping enum values to human-readable plan names and prices (e.g., 'personal-monthly' → JobDoneBot Personal 1480 JPY/month). It also clarifies that email is optional via the schema, but the description doesn't repeat that; still, the added pricing context gives value beyond 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?

The description clearly states the tool's purpose with a specific verb and resource: 'Create a checkout session for a JobDoneBot subscription.' It also distinguishes from siblings by focusing on creating a subscription checkout, while a sibling like check-subscription presumably checks status. The description lists concrete plan options, adding specificity.

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?

The description gives clear context: this tool is for initiating a subscription via a Stripe checkout session, and it lists the available plans. It doesn't explicitly mention when not to use it or point to alternatives such as check-subscription, but the purpose is unambiguous and no exclusion is needed for a simple subscribe action.

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