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

The readOnlyHint annotation already signals safety, so the bar is lower. The description adds valuable behavioral context beyond that: URLs never contain secrets, downloads require the X-API-Key, and files are not executed. This helps the agent reason about authentication and security without contradicting the annotation.

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 four short sentences that front-load the core action and output, then add authentication details, the upload alternative, and a safety note. Every sentence earns its place, and there is no filler or redundant restatement of the schema.

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 one-parameter, read-only file tool, the description covers the input, the returned artifact (metadata and download URL), and the follow-up authenticated download. It does not describe response fields or error behavior, but no output schema exists and the operation is simple enough that an agent can invoke it 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?

The schema has a single required fileId parameter, but the description never explains what fileId refers to, how to obtain it, or any constraints beyond the schema's uuid format. Since schema description coverage is 0%, the description should compensate, and it does not. The role of fileId is only loosely inferable from the verb phrase 'get file.'

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-resource pair: 'Get file metadata and an authenticated REST download URL.' It clearly identifies the tool's output and distinguishes it from upload by explicitly pointing to the multipart POST endpoint. There is no ambiguity about what this tool does.

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 description explicitly states the alternative for uploads: 'For upload use multipart POST /api/v1/messages/{messageId}/files with Idempotency-Key and field file.' It also explains how to consume the result: 'Download with your X-API-Key.' It does not enumerate sibling-tool alternatives, but no file-download sibling is present in the list.

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