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

Annotations already declare this is a non-idempotent, non-read-only, non-destructive operation. Beyond that, the description adds meaningful behavior: per-language upload_url values are returned, a PUT is required to those URLs, and subtitles are only materialized after a separate completion call. It doesn't cover re-upload/replacement semantics or auth needs, keeping it at 4 rather than 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?

Four short sentences, front-loaded with the action and then the follow-up workflow. Slightly repetitive phrasing ('you need to' three times) but nothing wasteful.

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?

Given an output schema exists, the description need not explain return values, yet it usefully flags the upload_url output and the mandatory completion step. Combined with annotations covering safety, this is complete for correct invocation; only edge cases like overwriting existing subtitles are unaddressed.

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 asset_ID and language_codes are already documented in the input schema. The description only echoes that languages are 'specified' and does not add format or constraint detail beyond the schema's ISO 639-1 note, 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 specific verb (upload) and resource (.srt/.vtt subtitle files) explicitly attached to a video asset, which is enough to separate it from thumbnail_upload or asset_audio_upload. It doesn't name its closest sibling (complete_subtitle_upload) by name, but the multi-step flow makes the boundary understandable.

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?

The description lays out the full required sequence: initiate the upload, PUT the files to the returned URLs, then call the subtitle upload complete API before subtitles appear. That gives clear ordering and prerequisite context, though it refers to the follow-up step descriptively rather than routing to the sibling tool name explicitly.

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