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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the trailing 'Side effects: none (read-only)' largely restates structured data. The real added value is the eventual-consistency warning that a 404 right after an upload means visibility lag rather than a failed send — a behavioral trait the 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?

Two short sentences, front-loaded with the purpose and followed by the highest-value caveat. The 'Side effects: none (read-only)' line is redundant against the annotations and is the only wasted text.

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 no explanation, and both parameters are fully documented in the schema. For a simple read-only single-record fetch, the only material omission is a note on when to choose this versus the outbox/report variants.

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%, with both fax_id and user_id documented including the 'Default: self' behavior, so the baseline of 3 applies. The description adds nothing about parameter format, ID source, or the implication of supplying user_id on behalf of another user.

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: 'Get details for a specific fax record.' An agent can tell this is a single-record fetch rather than a list operation. It does not, however, distinguish itself from close siblings like get-outbox-fax or get-fax-report, which an agent must resolve from names alone.

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 404-after-send caveat gives genuine timing guidance tied to send-fax-uploaded, which is useful. But there is no statement of when to prefer this over get-outbox-fax, get-fax-report, or list-faxes, so sibling selection is only implied by the resource name.

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