Top up credits

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

Annotations already declare readOnlyHint=true and openWorldHint=true; the description earns credit by explaining why a 'buy' tool is read-only ('never charges anything: the user picks the pack and pays in their browser'), which pre-empts the obvious wrong assumption. It also states the human-in-the-loop requirement. Minor gap: no note on link expiry or re-generation behavior.

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?

Four short sentences, front-loaded with the core action, followed by triggers and then the operating procedure. No filler or repetition; every sentence carries distinct information.

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 single-optional-parameter tool with no output schema, the definition covers the action, the trigger conditions, what the user must do, the safety property (no charge), and the post-call workflow. Nothing an agent needs to call or act on 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?

Schema coverage is 100%, and the schema already explains that creditsNeeded preselects the smallest covering pack. The description adds value by enumerating the actual pack sizes (500 / 1,500 / 5,000) and noting the optional auto top-up toggle, which the schema does not mention.

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?

Uses a specific verb and resource: 'Get the link where the user buys a credit pack.' It also names the pack tiers (500 / 1,500 / 5,000) and the auto top-up option, so the agent knows exactly what the tool returns, distinct from siblings like vivid_whoami or vivid_usage.

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 two explicit trigger conditions: a call that failed for lack of credits, or a big batch the balance from vivid_whoami will not cover. It also names the alternative source of truth (vivid_whoami) and prescribes the follow-up flow: show the link, wait for confirmation, then continue.

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