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

There are no annotations, so the description fully carries the behavioral burden. It clearly discloses that the tool mutates an existing layer, preserves its id/position/size/animations/styles/trim, and only changes the source mp4. This exceeds anything in the schema and is helpful. Still missing: any mention of error behavior if the referenced clip does not exist, or sync/async semantics, but overall 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?

The body is tightly structured: a first sentence describing the core action and preservation guarantees, followed by a second sentence giving the prerequisite and upload channels, and a short directive with the key value proposition. There is no repetition or filler; each sentence 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?

For a simple 3-parameter tool with no output schema, the description covers what an agent needs to call it correctly: it explains behavior, the constraints (clip already exists), and the primary use case. It lacks error-handling details (e.g., what happens when the clip is missing) and explicit permission needs, but the tool is simple enough that these details are not essential. Overall it is complete enough for likely agent usage.

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?

Since the input schema already provides strong descriptions for all three parameters (clip, elementId, projectId), the baseline is 3. The description adds extra meaning by stating the exact path users/<userId>/clips/<projectId>/<clip> and the allowed upload methods, which helps an agent construct the clip parameter correctly. This goes beyond the schema's file name mention, giving concrete constraints and context.

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 starts with a clear verb+resource: "Repoint an existing video layer at a different uploaded clip," then spells out exactly which layer attributes are preserved and which change. This cleanly differentiates it from siblings like set_video_layer_trim, remove_layer, or add_video_layer. The use case is unambigous and no tautology or restating of the name.

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 explicitly says 'Use this to swap a video layer's source WITHOUT losing its keyframes' and states the prerequisite that the clip must already exist at the specified path and be uploaded via specific means. It does not explicitly name alternatives or provides when-not conditions, but the target scenario is concrete and well-delineated from competing actions.

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