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

Goes well beyond the annotations: it discloses a 50-file cap, the replace-on-duplicate-path semantics that give meaning to idempotentHint, per-file validation on arrival, the staged/publish-gated behaviour, and the return payload (count plus total size). That is exactly the extra context annotations cannot carry.

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?

Five short sentences, each carrying a distinct fact (limit, overwrite rule, validation, return shape, publish gating), with the core action stated first. No filler or restatement of the title.

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 two-parameter tool with no output schema, the description covers return values, limits, validation, idempotency and the publish lifecycle. The only real gap is the origin/semantics of uploadId, which an agent must infer from start_upload.

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 0%, so the description must compensate and it only partly does: it explains the 'files' array limit and the replace-by-path rule, but says nothing about where uploadId comes from or what it identifies. Nested path/encoding semantics are covered by the schema, not the description.

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 (adds) and resource (files) plus the container (an open upload) and a hard limit (50 per call), which cleanly separates it from start_upload and publish_upload without naming them. It stops short of explicitly contrasting with the sibling tools, so it lands at 4 rather than 5.

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?

'Adds files to an open upload' establishes the prerequisite that an upload already exists, and 'Nothing goes live until the upload is published' steers the agent toward publish_upload as the follow-up step. There is no explicit when-not guidance or named alternative, but the workflow context is clear.

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