control-expert-mcp

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create_variable

Create a global variable in Control Expert PLC projects by specifying name and IEC type, with optional address and initial value.

Instructions

Create a global variable.

type_name is an IEC type ('BOOL', 'EBOOL', 'INT', 'DINT', 'REAL', 'TIME', 'STRING', ...), an array ('ARRAY[0..9] OF INT'), a DDT or a DFB type name. address is an optional topological address like '%MW100' or '%Q0.2.0'.

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": {
      "name": "<name>",
      "type_name": "<type_name>"
    },
    "name": "create_variable"
  }
}

Input Schema

Name	Required	Description	Default
`name`	Yes
`type_name`	Yes
`comment`	No
`address`	No
`initial_value`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Jun 14, 2026

TDQS

C2.7/5.0

Behavior2/5

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

With no annotations provided, the description must disclose behavioral traits. It only implies a write operation ('Create') without detailing side effects, reversibility, or error conditions. There is no mention of what happens on duplicate names, or required permissions, so behavioral transparency is minimal.

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

Conciseness4/5

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

The description is concise and front-loaded with the purpose, then details two key parameters efficiently. It avoids redundant phrasing, but the brevity comes at the cost of completeness for other parameters. Still, the structure is clear and focused.

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?

The tool has 5 parameters, no output schema, and no annotations. The description only covers two parameters and omits usage context, expected return, and any prerequisites or side effects. For a create operation, this is noticeably incomplete for an agent to rely on.

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

Parameters2/5

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

The schema has 0% description coverage, so the description must compensate. It explains type_name and address thoroughly, but name, comment, and initial_value are left undocumented. This partial coverage is insufficient for a 5-parameter tool with no schema descriptions for the remaining parameters.

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 states 'Create a global variable' clearly, with a specific verb and resource. It doesn't differentiate from sibling tools like update_variable or delete_variable, but the creation intent is unambiguous. It also gives examples of type_name and address, which adds clarity to the parameter semantics.

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?

There is no guidance on when to use this tool vs alternatives, nor any exclusions or prerequisites. The description only explains parameter formats, not the usage context or selection criteria. This leaves the agent to infer when creation is appropriate.

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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