Video captions

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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely new behavior: the ordered source waterfall (HTML5 tracks, YouTube captions, player network log) and the explicit 'reports clearly when none' outcome, though it doesn't describe result shape or pagination.

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: what it returns, where it looks, and what happens on failure. Fully front-loaded with zero 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 still says the return is captions with timestamps and that absence is reported explicitly, which is enough for an agent to interpret results. Only minor gaps remain (result format details, whether ranges are inclusive) and those are cheap to discover.

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% and every parameter (start, end, tabId, video, language) has a description, so the schema carries the semantic load. The description mentions none of them, so it adds no value beyond structured fields — 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 and resource ('Returns the captions/subtitles of a video with timestamps') and enumerates the sources it draws from. An agent can distinguish it from video_transcribe 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 names the alternative and the condition that selects it: 'Reports clearly when there are none (then use video_transcribe).' That is a direct when-to-use-this-vs-that routing rule, plus the source-order fallback behavior.

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