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

Annotations only indicate non-read-only and non-idempotent behavior. The description adds meaningful context: it requires Authorization, returns a checkout_url, and explains that the webhook credits within seconds. It doesn't contradict annotations and provides useful operational detail beyond the structured fields, though it doesn't cover failure cases or edge behavior.

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 two sentences with no filler. The core action is front-loaded, and every clause adds value: pack options, output, payment method, auto-crediting, and auth requirement. It is a model of concise, structured tool documentation.

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 single-parameter tool with an output schema (indicated in context), the description fully covers what an agent needs to call it: the action, the parameter values, the returned field ('checkout_url'), the interaction flow (pay and auto-credit), and the required authorization. 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?

The schema has no description for the 'pack' parameter (0% coverage). The description compensates fully by enumerating the valid values ('starter', 'growth', or 'scale') and directing to get_pricing for details. This gives the agent precise semantic guidance without needing the schema to be enriched.

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 specific action: 'Create a Stripe Checkout session for a credit pack', and lists the exact pack options ('starter', 'growth', or 'scale') with a pointer to get_pricing. This distinguishes it from siblings like check_balance or get_pricing, providing a precise verb-resource-scope combination.

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 clear usage flow: create session, pay, and the webhook credits the account. It also references get_pricing for pack details, implying that the agent should consult pricing first. However, it does not explicitly state when NOT to use this tool (e.g., when credits are insufficient on an existing account), so it falls short of a 5.

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