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

The annotations already establish this as a non-read-only, non-idempotent, non-destructive mutation. The description adds meaningful behavior beyond them: the call is project-scoped, it returns the project identity with the result, and it explicitly says 'length and sound never move', which tells the agent the edit does not alter timing or audio. It does not explain permissions or how partial/overlapping ranges behave, but the core behavioral disclosure is strong.

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 front-loaded with the project-scoping constraint and then gives the visual behavior and parameter hints in a compact block. Some phrasing is dense and poetic ('the upload's pictures run past horizontally', 'baked into one file or not'), but it remains readable and no sentence is clearly wasted.

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 seven-parameter visual mutation tool with no output schema and very low schema description coverage, the description covers the main effect, range semantics, visual options, and removal path. It still leaves the 'gap' parameter undocumented and does not clarify return structure beyond the project identity, so it is adequate but not fully complete.

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 only 14%, so the description needs to compensate. It does explain start/end as program seconds, direction as left|right, height as 0.3-1 of the frame, and backdrop as blur|black. It omits the 'gap' parameter entirely (0-0.2 range) and only restates project_id's scope rather than adding detail, leaving a notable semantic gap for a low-coverage 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 uses a specific verb and resource ('add filmstrip') and explains the visual result in concrete terms: horizontally running pictures, multiple frames in view, original colour/aspect, and blurred or black backdrop. It also explicitly differentiates from the sibling 'remove_filmstrip', so an agent can distinguish the operation without opening the 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?

The description implies the tool is used to add a filmstrip across a program range and names 'remove_filmstrip' as the undo/removal alternative. However, it does not state when to prefer this over related siblings such as add_collage, compose_panels, or add_region_effect, nor does it give any explicit exclusions or prerequisites beyond project scoping.

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