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

With no annotations, the description carries the full burden and does well: it discloses the third-party provider (Phaxio), the approval precondition, and exactly-once/idempotent transmission semantics. It stops short of noting side effects such as cost or what happens on partial failure.

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?

Two tight sentences: the action is front-loaded, followed by the refusal constraints. Every clause carries new information, with no restating of the title or 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 mutation tool with an output schema, the description covers the key behavioral contract (approval gate, single transmission). Return values are handled by the output schema, so nothing critical is missing, though operational side effects are unmentioned.

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% for both parameters, and the description adds no parameter-level detail beyond what the schema already states (fax_id provenance, api_key format). Baseline 3 applies when the schema does the heavy lifting.

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 ('Transmit an APPROVED fax via Phaxio') and scopes it to approved faxes only. It implicitly distinguishes itself from create_fax_draft/approve_fax by the approval precondition, but never names those siblings explicitly, so an agent must infer the workflow ordering.

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 refusal conditions ('refuses drafts that were never approved and faxes that were already sent') effectively communicate when not to use it. However, it does not name the alternative tools (approve_fax, create_fax_draft) an agent should call first, leaving the routing implicit.

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