mcp-esp32

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repl_exec

Run MicroPython code on an ESP32 board over its raw REPL, with separate stdout, stderr, and exception output for debugging.

Instructions

Run code on port over MicroPython's raw REPL; stdout/stderr/exception come back separately.

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": {
      "port": "<port>",
      "code": "<code>"
    },
    "name": "repl_exec"
  }
}

Input Schema

Name	Required	Description	Default
`code`	Yes
`port`	Yes
`timeout_s`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Jul 31, 2026

TDQS

A3.8/5.0

Behavior3/5

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

With no annotations, the description carries the burden of behavioral disclosure. It discloses that stdout/stderr/exception are returned separately, which is a useful behavioral trait. However, it does not mention potential side effects of arbitrary code execution, prerequisites like device connection, or error handling, leaving gaps for an agent.

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 sentence that is concise, front-loaded, and contains no filler. Every part—action, target, mechanism, and output result—is packed meaningfully, earning a high rating.

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?

The tool has moderate complexity with three parameters, no output schema, and no annotations. The description covers the core purpose and output separation, but it leaves out important details such as how to identify the port (though sibling list_ports exists), timeout behavior, and connection prerequisites. It is adequate but could be more complete by referencing sibling tools or clarifying expected behaviors.

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?

Schema description coverage is 0%, so the description must compensate. It gives meaning to 'code' and 'port' by stating 'Run `code` on `port`', but adds no detail about valid formats or constraints. The 'timeout_s' parameter is not mentioned at all, and the description does not sufficiently explain parameter values beyond restating names.

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 ('Run') and resource ('`code` on `port`'), and specifies the mechanism ('over MicroPython's raw REPL'). This clearly distinguishes it from sibling tools like list_ports and fs_ls, which handle ports and filesystem operations rather than code execution.

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

Usage Guidelines4/5

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

The description provides clear context for when to use this tool: when you need to execute Python code on a MicroPython device via raw REPL. It does not explicitly list alternatives or exclusion cases, but the context is sufficiently distinct from sibling tools that an agent can infer appropriate usage.

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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