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

Annotations already declare readOnly, idempotent, and non-destructive, so the safety bar is lower. The description still adds real context beyond them: prices are in cents per postcard and the call does not spend credits — a meaningful clarification for a wallet-adjacent endpoint.

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, with no filler. Minor redundancy: 'Get mail pricing' and 'Get postcard pricing' restate the same operation, and the no-write clause partly duplicates the readOnlyHint annotation.

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 read with full annotation coverage and no output schema, the description covers what the call does, its units, and its side-effect profile. It could say more about the shape of the response (e.g., whether volume tiers are returned), which is the only remaining gap.

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 tool takes zero parameters, so the baseline is 4. The description correctly implies pricing is derived from the caller's plan rather than any input argument, leaving nothing for an agent to supply or misconfigure.

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: 'Get postcard pricing for your plan,' with the unit ('cents per postcard') made explicit. It is distinguishable from sibling cost/balance tools like dealmachine_get_mail_campaigns_id_cost_estimate and dealmachine_get_mail_wallet_balance, though it never names those alternatives.

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?

Usage is only implied: an agent can infer this is the tool for looking up per-postcard prices before sending a campaign. There is no explicit guidance on when to prefer this over the cost estimate or wallet balance siblings, and no stated prerequisites (e.g., plan required).

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