download_file

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

Goes well beyond the readOnlyHint/idempotentHint annotations by disclosing that images are shown in the UI rather than to the AI model, that the agent only receives a success confirmation with path/size, and that oversized files are rejected with size details. The retry prohibition is also behaviorally valuable.

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?

Four sentences, each earning its place: purpose, UI-delivery behavior, size-limit rejection rule, and usage boundary. Front-loaded with the core action, no redundancy or filler.

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?

Complete for a single-parameter tool with rich annotations. The description covers what the tool does, what the agent sees, how failures behave, and when to use it. No output schema is present, but the confirmation/rejection details are spelled out in prose.

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 compensate. It adds meaning by framing 'path' as a file on the local filesystem and by referencing 'the same path' and 'path/size' in the confirmation output. It does not explicitly define path format (e.g., absolute vs relative), but for a single string parameter this is adequate.

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 opens with a specific verb and resource: downloads a file from the local filesystem and sends it to the UI. It distinguishes itself from siblings like upload_file (direction of transfer) and from content-reading tools by explicitly stating it is 'not for reading file contents yourself.'

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 when conditions ('transferring a file the user asked to see or receive') and when-not conditions ('not for reading file contents yourself'). Also provides a concrete operational rule: do not retry the same path after a size-limit rejection. While it does not name a specific alternative sibling, the context clearly routes the agent.

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