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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint false; the description adds explicit side-effect disclosure ('none (read-only)') and the return format (base64 image bytes in structured output), which helps the agent know what to expect beyond the schema. No contradictions.

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 short sentences with the core action first and the side-effect/return information in a compact second sentence. No filler.

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 simple read-only thumbnail retrieval with a full output schema and fully documented parameters, the description is sufficient. Side effect and return format are included, and nothing else is needed for correct invocation.

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?

Input schema documents both parameters with 100% coverage. The description does not add further parameter-level semantics, so baseline 3 applies. It does not include detail beyond schema.

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?

Description states a specific verb (Retrieve) and resource (fax thumbnail image), distinguishing it from siblings like get-fax (full fax record) and get-file (generic file). The word thumbnail makes the purpose unambiguous.

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?

No explicit when-to-use or alternative guidance, but the description clearly implies the tool is for thumbnail image retrieval, leaving the agent to infer it should be selected when image bytes, not full fax data, are needed. It does not name exclusions or other tools.

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