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

Adds substantial context beyond the annotations: required permission scopes, a two-phase confirm protocol, the guarantee that the first call mutates nothing, strict argument validation that refuses unknown fields by name, and the exact payload returned (summary plus confirm_token). This is consistent with readOnlyHint=false and destructiveHint=false since only the confirmed second call writes.

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?

Front-loads the action, then the permissions, then the call protocol; every sentence carries information and there is no filler. The telegraphic fragments ('Two calls.') and slightly awkward clause 'it checks the arguments as the change would' cost a bit of polish but not comprehension.

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?

No output schema exists, and the description does cover what the first call returns, which is the critical unknown. It stops short of describing what the confirming second call yields or what the agent should do next (upload parts, then complete), leaving the tail of the workflow to inference.

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 only 25%, with just confirm_token documented in the schema, so the description must carry size, type, and scope. It clarifies confirm_token's role and the 'same arguments' repeat requirement, but says nothing about what size, type, or scope mean or what values they accept, leaving the three required parameters opaque.

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?

Opens with a specific verb and resource ('Start a large upload in parts'), which is immediately distinguishable from sibling tools like complete_multipart_upload and abort_multipart_upload. It never names those siblings, so the agent must infer the lifecycle position rather than being told.

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 an unusually explicit when-to-use flow: call once with arguments, show the summary to the person, then call again with the same arguments plus confirm_token. It does not say when to prefer this over a plain upload link (get_upload_link) or when to abandon in favor of abort_multipart_upload, leaving lifecycle routing implicit.

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