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

Annotations already declare idempotent=true, destructive=false, openWorld=false, so the safety profile is partly covered. The description adds real value beyond that: the interface is 'private', sign-in is required, and a browser link fallback exists for clients without MCP Apps support — auth and access-scope information annotations cannot express.

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?

Three short sentences, front-loaded with the core action and scoped with the constraint afterward. No filler, though the 'before approving payment' framing is slightly indirect about what the tool actually returns.

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?

Covers sign-in requirements and the MCP Apps fallback, which matters for a UI-opening tool. With no output schema, though, it should state what 'open' produces (a review link/URL vs. an embedded view) and what the id refers to — both are left implicit.

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 0%, so the description must carry the burden of explaining the single 'id' parameter. It never mentions the id at all — not whether it is a fax ID, a review ID, or an upload token — so an agent cannot confirm what identifier to pass.

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 ('Open') and a concrete resource (the private upload/PDF review interface for an account fax), which separates it from siblings like get_fax_review or update_fax_review. It stops short of saying exactly what opening yields (a URL, a session, or an embedded view), leaving a small ambiguity.

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?

Provides sequencing context ('before approving payment') and a fallback condition ('works when the client cannot show MCP Apps'), which is genuine usage guidance. However, it never explicitly contrasts with get_fax_review or get_fax_status, so the agent must infer when this is preferred over those alternatives.

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