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

Annotations declare openWorldHint=true and readOnlyHint=false, but the description adds substantial context: required API key/OAuth token, that the call does not change the plan or charge a card, that local billing bypass skips Stripe and returns the console URL, and the stripe_not_configured error condition. This goes well beyond the annotation surface.

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?

Six sentences, each carrying distinct load: purpose, usage, auth, return value, non-mutation caveat, bypass behavior, error mode, and sibling routing. Purpose is front-loaded and there is no filler.

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?

With no output schema, the description correctly covers the return contract (url on success, stripe_not_configured error) and the environment-dependent variation. Auth, error modes, and side-effect scope are all present, so nothing needed to call it correctly 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 tool takes zero parameters, so the baseline is 4 and there is nothing for the description to document. Auth requirements are mentioned, but that is behavioral rather than parameter semantics.

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?

Opens with a specific verb+resource ("Create a billing portal URL") scoped to "the authenticated company." It also explicitly distinguishes itself from siblings by naming billing_checkout and billing_machine_pay, so an agent can route correctly without opening other schemas.

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?

Gives concrete when-to-use criteria (human needs to update payment method, view invoices, or change subscription) and explicit alternative routing ("To buy Pro, use billing_checkout" and what billing_machine_pay actually returns). Both the trigger and the exclusions are stated.

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