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

Annotations already declare readOnlyHint and idempotentHint, so the description adds limited behavioral context—it mentions returns sorted rates with price, delivery time, service type, but does not elaborate on rate limits, authentication, or processing constraints beyond what annotations cover.

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 description is two sentences with no filler, immediately stating the purpose and required inputs, then the output format and a value proposition. Every sentence earns its place.

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 rate comparison tool with an output schema, the description covers key inputs and outputs. However, it omits clarification that country parameters exist and can be changed (default US), which is relevant for international users.

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 description only repeats the core parameters (ZIP codes, weight, dimensions) without adding new semantic information like units or formatting nuances beyond the schema descriptions.

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 clearly states the tool compares shipping rates across multiple carriers (USPS, UPS, FedEx, DHL) for a package, distinguishing it from sibling tools like logistics.shipengine.carriers which lists carriers, or tracking tools that handle post-shipment.

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?

The description explains what inputs to provide (ZIP codes, weight, dimensions) but does not explicitly say when to use this tool versus alternatives like tracking or validation tools. It implies usage for rate comparison before shipping, but lacks exclusionary guidance.

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