index_explainer_sources

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

With no annotations, the description discloses important behaviors: caching and idempotency ('re-running skips already-indexed files'), return type (index_id), and environment requirement (TWELVE_LABS_API_KEY). This goes beyond the schema and helps the agent understand side effects and prerequisites. It does not mention external side effects (creating an index in Twelve Labs) but is adequately 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?

Three sentences each earn their place: purpose, usage/caching behavior, and return value/prerequisite. No fluff, front-loaded with the core action. Ideal conciseness.

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 (2 params, no output schema), the description fully covers the essential context: what it does, when to call, what it returns, how to use the result, and the required environment variable. It is complete for the agent to invoke correctly.

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% for both parameters, so the schema already documents their meanings. The description adds contextual value by explaining the purpose of the folder and the returned index_id, but does not add new parameter-specific semantics beyond what the schema provides. Baseline 3 is appropriate.

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 action ('Index a local folder of screen recordings and OBS videos with Twelve Labs') and its purpose ('so they can be searched semantically inside create_video_assembly'). This clearly distinguishes it from sibling tools like suggest_clips or create_video_assembly, which consume the index rather than create it.

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?

Provides explicit usage guidance: 'Call this once per folder' and explains re-run behavior ('indexing is cached, so re-running skips already-indexed files'). It also tells the user what to do with the return value (pass as explainer_index_id in create_video_assembly) and mentions the API key prerequisite. It slightly lacks explicit exclusions or alternative tools, but the guidance is clear.

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