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

Goes well beyond the annotations: a 10-minute dedup window returning the same pending session, a rate limit of 3 new sessions per hour, the negative-balance default adjustment, and the graceful failure shape (checkoutUrl: null, reason, dashboardUrl). The idempotentHint=false is consistent with the time-windowed dedup rather than an exact-call idempotency guarantee.

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?

A single dense paragraph but front-loaded with the core action and outcome before the optionality, limits, and failure mode. Every clause carries information, though the run-on structure makes it slightly harder to scan than a few shorter sentences would be.

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?

No output schema exists, and the description explains what is returned (the checkout URL) plus the alternate return shape on failure. For a one-parameter tool this leaves nothing an agent needs 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?

With 0% schema description coverage, the description carries the full semantic load: amountUsd is optional, defaults to the suggested amount (at least minimumUsd, higher when the balance is negative), and values below the minimum are rejected with the minimum echoed in the error. That fully compensates for the bare 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: open a Stripe-hosted Checkout page to add prepaid credits to this workspace and return its URL. It also scopes the agent's role ('the agent never enters card details'), which distinguishes it cleanly from the read-only sibling `balance`.

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 clear conditions: amountUsd optional with a defined default, sub-minimum amounts refused with the minimum in the error, and it points to `balance` as the source of minimumUsd. It does not explicitly state when NOT to use it versus alternatives, but the operational context is otherwise well covered.

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