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

With no annotations, the description carries the full burden and does so richly: one-time consumption of the ref, the 15-minute upload window, the 1-hour ref validity, local byte storage by the extension, owner-only MCP_LOCAL_SEND authorization, and the Rust extension prerequisite. This is exactly the behavioral context an agent needs for a multi-step upload flow.

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?

Dense and well front-loaded, leading with the create action, then the return values, then the operational steps. Slight redundancy between the opening authorization clause and the closing 'Requires a connected Rust extension' line keeps it from a perfect score.

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 multi-step, stateful upload tool this covers the full flow end to end: creation, the returned artifacts, the PUT mechanics with a curl example, the expiry windows, and the handoff to send_message/schedule tools. With an output schema present, return-value detail is a bonus rather than a requirement.

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 100%, so the schema already documents name, mime, size and target_session. The description's only parameter-relevant claim, 'target_session selects the account,' restates the schema description rather than adding new syntax or constraints, so the baseline of 3 applies.

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 precise verb+resource ('Create a one-time attachment upload slot') and immediately distinguishes itself from any listing/query sibling by describing the upload-slot lifecycle. It also names the downstream tools (send_message, schedule create/update) that consume the ref, so the agent knows this is a preparatory step, not a send.

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?

Explicit when-to-use and sequencing: PUT bytes within 15 minutes, then pass the ref to send_message or a schedule create/update within one hour. Exclusion is stated too ('No third-party URLs') along with the prerequisite of a connected Rust extension.

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