Writes a live RAPID variable's value through RWS by specifying the task, module, variable, and new value, so controller runtime data can be updated directly from an MCP client.
Write a RAPID variable's live value via RWS
| Name | Required | Description | Default |
|---|---|---|---|
| task | Yes | ||
| value | Yes | ||
| module | Yes | ||
| variable | Yes |
Changes observed during successful MCP inspections.
v3.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description only indicates a write operation without disclosing behavioral traits such as whether the value is persistent, if mastership is required, or what happens if the variable doesn't exist. Since no annotations are provided, this is a significant gap.
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 a single sentence, which is concise, but it lacks useful detail. It is not structured with any highlights or breaks, making it minimally helpful.
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?
Given the complexity of writing a variable via RWS (requires task, module, variable name, and value), the description is severely incomplete. It omits critical context such as the need for mastership, the format of the value (e.g., data type), and potential errors.
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?
The input schema has four required parameters with no descriptions, and the tool description does not clarify their meaning or expected formats. For example, 'value' could be a string representation of any type, but no hints are given.
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 clearly states the action (write a variable) and specifies the technology (via RWS). However, it does not explicitly differentiate from sibling tools like rs_write_variable, which may cause confusion.
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?
No guidance is provided on when to use this tool versus alternatives like rs_write_variable or rws_write_module. Prerequisites such as mastership or connection state are not mentioned.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.