list_transcript_languages

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

With no annotations, the description carries the full burden. It discloses the return format ('<code> - <name> (manual|auto-generated)') and accepted URL forms, which is substantial behavioral context. However, it doesn't mention potential side effects or errors, though as a listing operation these are likely negligible.

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?

The description is compact and well-structured: a one-sentence purpose, a usage note, an Args section, and a Returns line. Every sentence adds value, and the purpose is front-loaded.

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 the tool's simplicity (one parameter, no annotations), the description covers all necessary aspects: what it does, when to use it, parameter semantics, and return format. It is fully complete within its scope.

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?

The input schema has no descriptions for the 'url' parameter, but the description fully compensates by explaining accepted URL forms (watch, youtu.be, shorts, embed) and the bare 11-character video ID. This goes well beyond the schema's bare parameter name.

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: 'List the subtitle tracks available for a YouTube video.' This clearly distinguishes it from the sibling tool get_transcript, which fetches the transcript itself, while list_transcript_languages focuses on language availability.

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 provides two scenarios for when to use this tool: when you don't know which languages are available, or after get_transcript reports a language is unavailable. This directly references the sibling tool and gives actionable context.

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