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

No annotations are provided, so the description carries the full behavioral burden. It does disclose two valuable traits an agent could not infer elsewhere: localization is billed, and the accepted input differs by transport (stdio vs hosted). It says nothing about permission/auth requirements, overwrite or duplicate-ID behavior, or any size/format limits on the upload itself.

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 short sentences, front-loaded with purpose, then input modes and return values, then the sibling redirect. No filler or restatement of the tool name; every clause adds a fact an agent can act on.

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?

An output schema exists and the description wisely summarizes the return shape (storage paths for list_subtitles, localize_subtitle_file, download) rather than enumerating fields. But for a 6-parameter mutation tool with zero annotation coverage, the gaps around the localization parameters and billing/limit details leave an agent under-informed about how to call it correctly in the non-default cases.

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 0% across 6 parameters, so the description must compensate and it only partly does: file_path is explained well (local path vs public HTTPS URL), and the localization toggle is implied by "optionally localize it". The remaining parameters — context, glossary, source_language, target_languages — get no meaning at all, including the key interaction of whether target_languages is required when auto_localize is true.

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?

The description opens with a specific verb+resource ("Upload and save a subtitle file") and immediately scopes the optional side effect ("optionally localize it (billed)"). It also names the sibling it is not (localize_subtitles) and the downstream consumers (list_subtitles, localize_subtitle_file), so an agent can distinguish it from adjacent tools 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?

It gives a clear routing rule: use localize_subtitles instead "for the existing in-memory workflow", which is an explicit when-not with a named alternative. It also constrains the input mode (local path under stdio, public HTTPS URL under hosted). It stops short of covering the other plausible alternatives (parse_subtitle, localize_subtitle_file) or stating what file types/sizes are acceptable.

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