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

Annotations declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the safety profile is already covered. The description adds genuinely useful behavior beyond that: it discloses the return value (media ID), its role in the workflow, and the non-obvious carousel batching rule. It does not mention failure modes such as an expired or uncompleted upload, which would have earned a 5.

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?

Three tight sentences, front-loaded with the precondition, then the return value, then the edge case. Every clause carries information an agent needs; there is no filler.

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?

With no output schema, the description correctly supplies the return value and its consumer (create_post), which is exactly what is missing from structured data. It is slightly incomplete on what happens if the upload never landed at the URL or the uploadId is stale, but for a one-parameter finalizer it is close to sufficient.

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?

Single parameter with 100% schema description coverage; the schema already explains that uploadId is 'returned by create_upload_url'. The description restates the same provenance plus carousel ordering, adding little semantic depth beyond the schema, so the baseline 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 ('finish upload'), names the prerequisite tool (create_upload_url) and the downstream tool (create_post), so it is distinguishable from siblings like upload_media_from_url or open_upload_box 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?

Explicitly defines the trigger condition ('After the file was uploaded to the URL from create_upload_url'), the required input, and the follow-up step ('pass to create_post'), plus the special carousel case with ordering instruction. The sequencing leaves nothing to inference.

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