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AE MCP Server

AE MCP Server

by p10q
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TypeScript
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set_expression

Apply expressions to layer properties in After Effects compositions to automate animations and effects. Specify composition ID, layer index, property path, and expression code.

Instructions

Set an expression on a 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": {
      "compId": "<compId>",
      "layerIndex": "<layerIndex>",
      "propertyPath": "<propertyPath>",
      "expression": "<expression>"
    },
    "name": "set_expression"
  }
}

Input Schema

NameRequiredDescriptionDefault
compIdYesID of the composition
layerIndexYesIndex of the layer
propertyPathYesProperty path (e.g., 'Transform.Position', 'Transform.Scale', 'Effects.Gaussian Blur.Blurriness')
expressionYesThe expression code to set
enabledNoWhether the expression should be enabled

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.0.0

TDQS

C2.9/5.0
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 states the action ('Set an expression') but lacks details on permissions, side effects, error handling, or what happens to existing expressions. For a mutation tool with zero annotation coverage, this is a significant gap in transparency.

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, efficient sentence that directly states the tool's purpose without unnecessary words. It's front-loaded and wastes no space, making it easy to parse quickly.

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

Completeness2/5

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

Given the complexity of setting expressions (a mutation operation), the lack of annotations and output schema means the description should do more to explain behavior, return values, or error cases. It's insufficient for a tool that modifies layer properties without additional context.

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?

The schema description coverage is 100%, with all parameters well-documented in the input schema. The description doesn't add any additional meaning beyond what the schema provides, such as examples of property paths or expression syntax. This meets the baseline for high schema coverage.

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

Purpose4/5

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

The description clearly states the verb 'Set' and the resource 'expression on a layer property', making the purpose specific and understandable. However, it doesn't explicitly differentiate from sibling tools like 'add_expression_control', 'add_loop_expression', or 'batch_set_expressions', which prevents a perfect score.

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 like 'add_expression_control' or 'batch_set_expressions', nor does it mention prerequisites or context for setting expressions. Without any usage instructions, the agent must infer from the tool name and parameters alone.

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

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