Save an attachment to disk

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

Annotations already declare readOnlyHint=false (a write to disk) and openWorldHint=true, so the mutation profile is structured. The description adds that the file lands on the local machine and that the path is returned, but does not disclose overwrite behavior, permission requirements, or the directory restrictions and prompt-injection warning that live only in the schema.

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 action and return value, then identification, then the alternative tool. No wasted words.

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?

No output schema exists, and the description supplies the return value (the saved path). Combined with schema-level documentation of directory rules and the explicitly named alternative, an agent has everything needed to call this correctly.

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 80%, so the baseline is 3, but the description earns more by explaining the relation between the two identifier parameters and the single-attachment fallback — semantics that the per-field schema text does not spell out. It omits the directory parameter entirely, which the schema covers.

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 ('Download an email attachment to a folder on this computer') plus the return value (its path). It explicitly distinguishes itself from the sibling read_attachment, so an agent can choose between them without opening either schema.

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?

Gives explicit selection guidance: identify by partId or filename from read_email, and neither is needed when the email has exactly one attachment. It also names the alternative tool with the condition that selects it ('to have Claude read the contents instead').

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