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

With no annotations, the description carries the full burden, and it discloses the key behavioral trait that the second track is offset to start after the last cue of the first plus an optional gap. It doesn't discuss return format or edge cases, but the core transformation behavior is transparent.

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?

Two sentences that front-load purpose and behavior with concrete examples and no filler. Every phrase earns its place.

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?

The description plus the fully described schema give an agent enough to select and call the tool: required inputs, optional gap, output format enum, and offset behavior are all covered. The return value is not explicitly described, but the tool's simplicity and lack of an output schema make this a minor gap.

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% (all 4 parameters have descriptions), so the baseline is 3. The description only adds a mention of 'optional gap', which maps to gap_seconds, but provides no additional semantic detail beyond the schema.

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 states a specific verb ('Append') and resource ('subtitle track'), and gives concrete use cases (CD1 + CD2, second language track). This clearly distinguishes it from siblings like split_subtitles, retime_subtitles, and convert_subtitle.

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 implies when to use it: when combining two sequential subtitle tracks into one, with examples. It doesn't explicitly name alternatives or exclusion conditions, but the sibling list and the offset behavior make the intended use clear.

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