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

The description's 'Side effects: modifies multiple fax records' adds a clear statement of mutating behavior, but this largely restates the destructiveHint=true annotation. It does not disclose additional behavioral traits such as whether the operation is reversible, whether comments overwrite or append, or whether partial failures are possible.

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?

The description is short, front-loaded with the core purpose, and readable. The second sentence on side effects is somewhat redundant with the destructiveHint annotation but still serves as a useful explicit reminder and does not add meaningful bloat.

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 mutation tool with rich annotations, a fully described input schema, and an output schema present, the description covers the essential what and the key side effect. The main missing piece is explicit routing guidance relative to sibling bulk-update and single-update tools, but the schema and annotations carry enough context 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?

Schema description coverage is 100%, so the schema already documents payload and user_id. The description adds a small amount of semantic context by naming is_read and/or comment as the updatable fields, but it does not significantly enrich the parameter meaning beyond what the schema provides.

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 states a specific action and resource: 'Update multiple fax records in one request', with the two relevant fields (is_read and/or comment). It is clear what the tool does, but it does not explicitly distinguish this from the sibling bulk-update-outbox-faxes, relying on the tool names to carry that distinction.

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 phrase 'Update multiple fax records in one request' implies this tool is for batch updates rather than single-record updates, and the sibling update-fax suggests a single-fax alternative. However, there is no explicit guidance about when to prefer this tool over bulk-update-outbox-faxes or update-fax, and no exclusions are mentioned.

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