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

Goes beyond the destructiveHint/openWorldHint annotations by disclosing the concrete real-world consequence — postcards are physically mailed, the action is irreversible, and the user's account is charged. That financial cost is not encoded in any structured field and is exactly the context an agent needs before a destructive call.

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 tight sentences, front-loaded with the action, then the risk, then the preconditions. No filler or redundant restatement of the schema.

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 two-parameter terminal action with no output schema, the description covers the source of the token, the approval gate, cost, and irreversibility. Nothing needed to call it safely is absent.

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 description coverage is 100% and both parameters are well documented, so the description only needs to reinforce. It does add the linkage that confirmation_token comes from the preview call, but largely restates what the schema already says about confirm=true and explicit approval.

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 and resource ('Mail the postcards') plus the exact artifact it operates on (those approved in spur_preview_postcard_campaign), which cleanly separates it from the preview sibling and from spur_send_letters.

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?

Clearly establishes the prerequisite chain: the campaign must first be approved via spur_preview_postcard_campaign and you must pass its confirmation_token. It implies but does not explicitly state the negative case (what to do if no preview exists or the user has not approved) beyond the confirm=true requirement.

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