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

With no annotations, the description carries the full burden. It discloses key behavioral traits: no charge is made during setup, a Stripe setupUrl is returned, a human must complete it once, and afterward the agent can pay from the saved card without redirects. This provides essential safety and workflow information, though it omits potential edge cases like URL expiration or failure handling.

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, front-loaded with the primary purpose and followed by the workflow details. Every sentence contributes meaning with no redundancy or 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?

The tool has one parameter, no output schema, and no annotations. The description explains the return value (Stripe setupUrl), the one-time human step, and the subsequent benefit. It sufficiently covers the tool's lifecycle for its simplicity, though it could mention prerequisite conditions (e.g., valid api_key) or post-setup verification steps.

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 input schema has only one parameter, api_key, with a clear description ('Your vm_live_ API key'), giving 100% schema coverage. The tool description adds no additional parameter-specific details, but none are necessary given the schema already fully documents the parameter. Baseline 3 is appropriate.

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 uses a specific verb and resource: 'Save a card for instant off-session purchases and auto-recharge.' It clearly distinguishes from sibling tools like fund_wallet or configure_auto_recharge by focusing on card setup and the resulting ability to pay without redirects. The purpose is unmistakable.

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 explains when to use the tool: to establish a saved card for off-session purchases and auto-recharge, with a human completing a one-time Stripe setup. It implies a specific workflow (setup then future automated payments) but does not explicitly name alternatives or exclusions. Still, the context is clear enough for an agent to decide.

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