Get a checkout link for a paid plan

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

The description explicitly discloses side effects: 'This tool charges NOTHING and changes nothing' and explains that the human must pay on Stripe's page. It also clarifies that plan size is never changed from here, only via the human's click on the emailed agree link. This goes beyond the annotations (readOnlyHint=false, idempotentHint=true) by explaining exactly what side effects do and do not occur, providing valuable behavioral context.

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 slightly longer than minimal but every sentence serves a purpose: it states the action, clarifies side effects, gives usage conditions, and covers the edge case. The main action is front-loaded, and the additional sentences provide necessary safety and behavioral context. It is well-organized and not redundant.

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 tool with one parameter and no output schema, the description is comprehensive. It explains what the tool returns (checkout link or existing plan), how it should be handled (hand to human, do not submit), and the exact side-effect behavior. An agent has all the information needed to call it correctly and interpret the result.

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 already documents the single 'blocks' parameter with a description ('Number of 200 GB blocks (default 1)') at 100% coverage. The description mentions 'N x 200 GB blocks' but adds no new semantic detail beyond the schema. The baseline of 3 applies because the schema carries the parameter meaning.

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 opens with a specific verb and resource: 'Get a Stripe-hosted checkout link for a paid plan of N x 200 GB blocks at $5/month per block.' It clearly states what the tool does, distinguishing it from siblings like 'usage' or 'plan' by focusing on the checkout link generation. The scope is unambiguous.

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 gives explicit when-to-use guidance: 'Call it only when the human has asked for more space, and hand the link back to them; do not open or submit it yourself.' It also provides a when-not condition (do not open/submit) and an edge-case behavior (if already on a paid plan, returns the plan). It does not name specific alternative tools, but 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.