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

Annotations cover the mutation profile (readOnlyHint=false, destructiveHint=true, idempotentHint=false, openWorldHint=true), and the description adds substantial behavior beyond that: state-dependent branching (first scene vs. chained scene), the activation side effect a stream requires, the auto-switch wiring that chains a 24/7 channel, and a hard refusal condition (previous scene must already contain a video playlist layer). It also discloses a silent failure mode — audio files produce a video playlist holding audio and are not reported as an error — which is exactly the kind of non-obvious trait an agent needs.

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?

Roughly six dense sentences, but the highest-value information (what it does, that it is the normal path, the state-dependent behavior) is front-loaded, and the sibling routing notes are consolidated in the back half. It is longer than strictly necessary — the overlay/Studio sentence could be trimmed — but nearly every sentence carries actionable content.

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?

For a 7-parameter mutation tool with no output schema, the description covers purpose, branching behavior, prerequisites and refusal conditions thoroughly, which is more than enough to invoke it correctly. The one remaining gap is that it does not hint at what comes back (e.g. the new scene id), which matters slightly given there is no output schema.

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%, so the schema already documents every parameter, and the baseline is 3. The description still adds meaning the schema lacks: the provenance and encoding prerequisite for file ids, and the note that loop is ignored when the scene auto-switches into another one. It stops short of adding format or aggregation detail for the remaining parameters.

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 first sentence states a specific verb and resource ('Add a scene to a project and fill it with a video playlist') and frames it as the canonical way to add content. It explicitly distinguishes itself from siblings livereacting_set_playlist (for changes afterwards) and livereacting_add_layer (for audio playlists), so an agent can route correctly without opening other schemas.

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?

Gives explicit when-to-use context ('the normal way to put content into a project, because a new project is created empty'), prerequisites (file ids from livereacting_list_media or livereacting_import_media, files must have finished importing and encoding), and named alternatives for adjacent needs (livereacting_set_playlist for edits, livereacting_add_layer for audio). It even states what cannot be done here (text/image/interactive overlays, Studio only).

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