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

Annotations mark readOnlyHint=false, indicating the tool may have side effects (e.g., creating a billing portal session). The description only says 'returns the URL' and gives no hint about side effects or state changes. It adds no behavioral context beyond what annotations already imply, and fails to explain the non-read-only nature.

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?

Two concise sentences, front-loaded with the core action, followed by use cases and a prerequisite. No wasted words; every clause adds value.

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 simple one-parameter tool with no output schema, the description covers the purpose, return value, usage precondition, and key source. It lacks error handling or edge-case notes (e.g., what if no paid plan), but these are minor given the tool's simplicity.

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 100% with api_key already documented, but the description adds context that the key is 'received at signup,' which goes beyond the schema's 'sk_live_…' placeholder. This extra guidance helps the agent locate the correct key.

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 states a specific verb and resource: 'Returns the URL of Stripe's customer portal' and lists concrete use cases (change payment method, receipts, cancellation). It is clearly distinguishable from sibling tools like create_checkout or get_session, none of which serve the same billing-portal purpose.

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 provides a clear precondition: 'Can be used after subscribing to a paid plan.' It also notes the required api_key. However, it does not explicitly name alternative tools or say when NOT to use it, so it falls slightly short of full routing guidance.

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