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

The description explicitly states the side effect: 'queues outbound fax for delivery.' This is consistent with the destructiveHint=true annotation, which already warns of side effects. The description adds a bit of context by naming the specific side effect, but it does not go beyond to mention costs, rate limits, or the fate of the original fax. Given that annotations already flag destructiveness, this adds marginally useful context without contradiction.

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 exactly two sentences, with no filler. The first sentence delivers the core purpose and method, and the second adds the side effect. It is front-loaded and every word 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?

The tool has 11 parameters with full schema coverage and an output schema (has output schema: true). The description covers the essential purpose and side effect, which is sufficient for an agent to decide when to invoke it. It could mention explicit differences from send-fax-uploaded, but that is not essential given the clarity of the core action. Overall, it provides adequate context for a correctly specified tool.

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%, so all parameters are already documented in the input schema. The description adds a minor clarification that 'to must be an array of destination numbers' and reinforces the role of from_fax, but does not add significant meaning beyond the schema. Since the schema handles the heavy lifting, a baseline of 3 is appropriate per the rubric.

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 clear verb ('Queue') and resource ('new outbound fax') along with the specific method ('reusing an existing fax file reference via from_fax'). This distinguishes it from siblings like send-fax-uploaded, which likely sends a new fax from an uploaded file, so an agent can immediately understand the tool's purpose.

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 clearly implies when to use this tool: when you want to resend an existing fax by referencing its file via from_fax. It does not explicitly name alternative tools, but the phrase 'reusing an existing fax file reference' and 'Queue a new outbound fax' clearly set the context. While it doesn't say 'use send-fax-uploaded instead for new documents', the purpose is unambiguous enough for an agent to infer the appropriate use case.

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