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

With no annotations, the description carries the burden, and it does disclose the four possible status values and the important fact that the call is free — useful behavioral context. It omits whether status is eventually consistent or should be polled, what happens for an unknown id, and any rate-limit or permission notes.

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 very short sentences, front-loaded with the action, followed by the return-value enumeration and the cost note. Nothing is padded or redundant.

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 single-parameter read tool with no output schema, the description covers the action, the possible return states, and the cost behavior. Only minor gaps remain, such as error handling for unknown ids and whether repeated polling is the intended pattern.

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 coverage is 100% and the schema already explains fax_id as 'The id returned by send_fax'; the description's 'by id' adds no meaning beyond that. Baseline 3 is appropriate since 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 ('Read one fax by id'), which is clearly distinguishable from the sibling send_fax (which creates) and quote_fax (which prices). The 'Does not charge' clause further signals it is the non-mutating lookup, though it never names the siblings explicitly.

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?

Usage is implied: look up a fax when you have an id from send_fax, without incurring cost. There is no explicit when-to-use vs when-not-to-use guidance, no mention of polling for in-progress status, and no exclusions relative to quote_fax or send_fax.

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