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

Annotations only cover the coarse profile (openWorldHint=true, destructiveHint=false), so the description carries real additional value: server-side fetch semantics with SSRF protection (internal/private addresses blocked), a 50 MB cap, no-truncation guarantee, and an authorization tier requirement. These are exactly the failure modes an agent needs to know before calling.

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?

Six compact sentences, each carrying a distinct fact (mechanism, routing rule, size limit, optional param, alternative tool, permission). The purpose and mechanism are front-loaded before the constraints.

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 4-parameter create tool with no output schema, the description covers the mechanism, preconditions, limits and the competing sibling. Since there is no output schema, it does not need to describe return values, and the idempotency/replay behavior is fully documented in the schema.

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 100%, so url, taskId, fileName and idempotencyKey are already documented at the schema level. The description restates only the fileName derivation rule and the public-URL constraint, both of which the schema already states, so it adds no meaningful syntax or format detail beyond the baseline.

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 ('Attach a file to a task by URL') and immediately explains the mechanism — the server fetches the bytes rather than the model. It contrasts itself with the sibling 'upload_task_attachment' so an agent can route correctly without opening any 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 when-to-use ('when the file already lives at a URL — cloud storage, a public link'), an explicit alternative for the other case ('file that exists only in your sandbox, use upload_task_attachment instead'), and a permission precondition (contributor or above; VIEWERs cannot). Nothing is left to inference.

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