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

Annotations cover the read-only/idempotent/non-destructive profile, yet the description adds substantial non-obvious behavior: sample/test items return cost_cents 0 with live_cost_cents showing the real price, proposals never charge credits or buy postage, destinations are validated against the agent's inbound policy, and denial should halt the agent. This is rich context beyond the structured fields.

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 core purpose and the chaining instruction are front-loaded, which is good, but the text runs long and mixes in tangential boilerplate (image URLs never issued to agents, never switch keys or mail APIs) that does not help an agent invoke this specific pricing tool.

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?

With an output schema present, the description needn't explain returns, yet it still clarifies the cost_cents/billable breakdown and the sample-item case. Combined with permission scope, side-effect guarantees, and the explicit hand-off to request_inbound_action, an agent has what it needs; only error/denial handling detail is thin.

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 (item_id, postal_code) are fully documented in-schema, so the baseline is 3. The description reinforces that postal_code is a US ZIP destination but adds no format or syntax detail beyond what the schema already provides.

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 states a specific verb and resource ('Price every forwarding class for an item to a US ZIP') and even names the endpoint GET /v1/inbound-items/:id/forward-quote. It is clearly distinguishable from the sibling quote_outbound_mail, which prices outbound mail rather than inbound forwarding classes.

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?

It gives explicit downstream usage: pick a class and pass { cost_cents, billable, max_cents: cost_cents } as action.expected_quote to request_inbound_action. It also states key-scope rules (member keys read own items, agent keys read bound/assigned items). It stops short of stating when NOT to use it versus alternatives, but the context is clear.

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