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

With no annotations, the description carries the full behavioral burden and does much of it well: it discloses the side-effect profile ('NEVER transmits anything'), the read-like validation/screening steps, and the exact cost model (per-page cost x pages + flat $1.00 fee). It omits auth scope beyond the api_key param and any rate/latency notes, so it falls short of a 5.

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 tightly written sentences. The verb+resource is front-loaded, followed by the behavior summary and the workflow handoff, with no wasted clauses.

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?

An output schema exists so return values need not be explained, yet the description still summarizes the quote. Purpose, non-destructive behavior, and workflow routing are all covered for a 4-param tool with full schema coverage.

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 the schema already documents all four parameters (api_key, to_number, pdf_path, description). The description implies recipient validation and PDF page counting but adds no syntax or format detail beyond what the schema provides, so the baseline of 3 is appropriate.

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 names a specific verb+resource ('Create a fax DRAFT') and enumerates the exact work performed — recipient validation, page counting, text screening, and a price quote. It clearly distinguishes itself from the transmitting siblings by stating 'This NEVER transmits anything,' so an agent can tell it apart from send_fax without opening either schema.

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 provides explicit workflow context: 'call approve_fax, then send_fax,' placing this tool as the first step and routing the agent to the correct successor tools. It doesn't spell out when-not-to-use beyond the non-transmission distinction, but the sequencing guidance is clear and actionable.

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