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

Annotations carry the safety profile (readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false). The description adds crucial behavior beyond annotations: cost and currency, on-chain payment requirement, that the result is a reusable bearer token, and critically the accounting rule that failed calls are free — a non-obvious, high-value detail.

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?

Three sentences, all load-bearing: what/how (purpose, payment), what you get (token), and how/when usage applies (per-call consumption, failed calls free). No filler, front-loaded.

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 zero-parameter purchase tool, everything needed to call it correctly is present: cost, payment network, artifact returned, and the exact consumption mechanism on sibling tools. No output schema exists, but the description compensates fully by describing the returned token and its lifecycle.

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?

Input schema has zero parameters (baseline 4). The description still adds meaning by explaining that the purchase's output is a token to be injected as params._meta['creatinginai/pack'] on sibling tools, which is the real parameter semantic an agent needs.

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 (Buy), resource (a pack of 20 paid calls), price ($1.00), and payment channel (x402 in USDC on Base) in a single sentence. Clearly distinguishes itself from data-retrieval siblings like atlas_kit/atlas_draft by being the payment instrument that feeds them.

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?

Explicitly states when to use it (to avoid paying per call) and exactly how the returned token is consumed (send as params._meta["creatinginai/pack"] on atlas_kit or atlas_draft). Names the downstream tools, so the purchase-to-use flow is unambiguous.

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