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

Goes well beyond the annotations by disclosing the two-stage async model: success only means the library accepted the file, while Meta-side processing continues and must be polled via fetch_creative_details. That is exactly the non-obvious behavior an agent would otherwise get wrong. Annotations (readOnly=false, destructive=false, openWorld=true) do not convey any of this.

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: purpose first, mechanism second, the critical async caveat and next step last. No repetition of the title and 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?

Covers purpose, mechanism, and async success semantics for a write tool with no output schema. The one gap is that it never says what identifier comes back (e.g., a library/creative ID) to feed into fetch_creative_details, which matters for chaining.

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 videos, usage_type (CTV enum) and thumbnail_library_id are already fully documented in the schema. The description only restates that URLs are downloaded and uploaded, adding no format, size, or validation detail beyond the schema. 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?

Specific verb+resource: uploads video files into the Metadata platform library, and explicitly states it downloads from provided URLs first. It is clearly separable from upload_image_creative / upload_document_creative (different media) and from create_update_video_ad (which builds the ad, not the asset).

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 routes the agent: after upload, use fetch_creative_details to read per-channel status before creating a Facebook or Instagram video ad, and the schema-level usage_type covers the CTV case. It gives clear context but no explicit exclusions (e.g., when to prefer an already-uploaded library creative or search_library_creatives_by_name).

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