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

No annotations are provided, so the description carries the full burden. It discloses key behaviors: upgrades are charged immediately and prorated, downgrades/cancellations take effect at period end, and 'A plan change never deletes snapshots.' It also mentions the billing intervals and free cancellation. However, it doesn't specify what happens to existing snapshots if the plan is downgraded (e.g., if they exceed the new limit), which is a minor gap.

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 well-structured and front-loaded: it starts with the core action, then details the plans, billing behavior, and ends with a critical safety instruction. Every sentence adds value, and it's concise given the complexity of the pricing logic.

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 3 parameters, no output schema, and no annotations. The description covers the plan details, billing behavior, and safety confirmation. It's complete for the agent to understand the tool's function and side effects. However, it doesn't mention what the response looks like (e.g., confirmation of the change) or any error conditions, but given the lack of output schema, this is acceptable.

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%, so the schema already documents all three parameters. The description adds value by explaining the plan options (pro, max, free) with storage and snapshot details, and clarifies that 'free' cancels at period end. It also explains the interval options (month/year) with the 'two months free' benefit. This goes beyond the schema's basic descriptions.

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 clearly states the tool's purpose: 'Change the wallet’s Agent Vault plan, charged from platform credits.' It specifies the resource (Agent Vault plan) and the action (change/subscribe), and distinguishes it from sibling tools like vault_list_snapshots or vault_usage by focusing on plan changes.

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 explicit usage guidance: it explains when to use the tool (to change plans), what each plan entails, and includes a critical instruction: 'ALWAYS confirm the plan and the charge with the user before calling.' It also clarifies that downgrades/cancellations take effect at period end, which helps the agent decide when to use it.

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