After Effects MCP Server

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setLayerExpression

Set or remove a JavaScript expression on a specific layer property in an After Effects composition; pass an empty string to remove it.

Instructions

Set or remove an expression for a specific layer property.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "compIndex": "<compIndex>",
      "layerIndex": "<layerIndex>",
      "propertyName": "<propertyName>",
      "expressionString": "<expressionString>"
    },
    "name": "setLayerExpression"
  }
}

Input Schema

Name	Required	Description
`compIndex`	Yes	1-based index of the target composition in the project panel.
`layerIndex`	Yes	1-based index of the target layer within the composition.
`propertyName`	Yes	Name of the property to apply the expression to (e.g., 'Position', 'Scale', 'Rotation', 'Opacity').
`expressionString`	Yes	The JavaScript expression string. Provide an empty string ("") to remove the expression.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Oct 17, 2026

TDQS

B3.3/5.0

Behavior2/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It only states that expressions can be set or removed, but does not disclose side effects such as overwriting existing expressions, handling of invalid expressions, or whether the target property must exist. The removal behavior via empty string is only implied, not explicitly stated in the description itself.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, front-loaded sentence that directly states the tool's purpose without any filler. Every word earns its place, making it highly concise and scannable.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the moderate complexity (4 required parameters, no output schema, no annotations), the description provides the essential purpose but leaves gaps around behavioral outcomes and edge cases (e.g., overwriting, error handling, prerequisites). The schema covers parameters well, but the lack of behavioral context makes the description only minimally complete for an agent to safely invoke the tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Since the schema already provides 100% coverage with clear descriptions for all four parameters, the description adds minimal extra semantic value beyond mentioning 'remove' in the summary. The schema describes expressionString's empty-string behavior effectively, so the description does not need to compensate for missing parameter details.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description uses a specific verb ('set or remove') and resource ('expression for a specific layer property'), clearly distinguishing it from sibling tools like setLayerKeyframe (keyframes) and run-script (general scripts). It precisely conveys both the primary action and the removal capability.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides no guidance on when to use this tool versus alternatives, nor does it mention any prerequisites or exclusions. Usage context is only implied by the tool's name and purpose, but no explicit when-to-use or when-not-to-use guidance is given relative to siblings like run-script or setLayerKeyframe.

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