mcp-snap7

by daedalus

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Python

Local

ct_read

Read counter values from a Siemens PLC by specifying start byte offset and number of bytes.

Instructions

Read counters from PLC.

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": {
      "start": "<start>",
      "size": "<size>"
    },
    "name": "ct_read"
  }
}

Input Schema

Name	Required	Description	Default
`start`	Yes	Start byte offset
`size`	Yes	Number of bytes to read

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Jun 8, 2026

TDQS

B3.2/5.0

Behavior3/5

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

The description implies a non-destructive read operation, which is typical. However, no annotations are provided, and the description does not mention any potential side effects or constraints (e.g., blocking behavior, required preconditions).

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?

Extremely concise, front-loading the key information. However, it is arguably too short given the context of many sibling tools.

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?

With an output schema present, return values are covered. But the description does not differentiate from other read tools or explain what 'counters' means in this context, leaving the agent to infer from the tool name.

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?

Schema coverage is 100%, so the description adds no extra meaning beyond the parameter names and their schema descriptions. It does not clarify the unit or format of offsets and sizes.

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 action (Read) and resource (counters from PLC), giving a specific purpose. While it distinguishes from write tools, it does not differentiate from other read tools like ab_read or db_read.

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?

No guidance on when to use this tool over alternatives. With many sibling read tools, the description lacks context for selection (e.g., when to choose counters vs analog blocks).

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