can-engineering-mcp

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add_or_update_signal

Create or update a CAN database (DBC) signal, optionally auto-packing it into the first free bit block and rejecting bit-overlapping writes.

Instructions

Create or update a signal; auto_pack=True finds the first free bit block. Rejects bit-overlapping writes.

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": {
      "dbc_path": "<dbc_path>",
      "message_id_or_name": "<message_id_or_name>",
      "signal_name": "<signal_name>",
      "length": "<length>"
    },
    "name": "add_or_update_signal"
  }
}

Input Schema

Name	Required	Default
`unit`	No
`scale`	No
`length`	Yes
`offset`	No
`dry_run`	No
`max_val`	No
`min_val`	No
`dbc_path`	Yes
`auto_pack`	No
`is_signed`	No
`mux_value`	No
`receivers`	No
`start_bit`	No
`byte_order`	No	little_endian
`signal_name`	Yes
`value_table`	No
`mux_is_switch`	No
`message_id_or_name`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Nov 3, 2026

TDQS

C2.7/5.0

Behavior2/5

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

With no annotations, the description must carry the full behavioral burden. It discloses auto_pack packing behavior and rejection of overlapping bit writes, but omits critical mutation details such as what happens to an existing signal, how dry_run behaves, permission requirements, and broader side effects.

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 very tight and front-loaded: it states the core action first, then the auto_pack behavior and overlap rejection. It is appropriately concise, though that concision contributes to under-specification elsewhere.

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?

For an 18-parameter mutation tool with no annotations and no output schema, the description is far too sparse. It covers only two behavioral points and leaves most parameters and mutation semantics for the agent to infer.

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% and there are 18 parameters, so the description must compensate heavily. It only explains auto_pack semantics and the overlap rejection condition; the other parameters, including start_bit, byte_order, mux_value, receivers, and dry_run, remain undocumented.

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 a specific verb and resource: "Create or update a signal". It does not explicitly distinguish this from sibling tools like upsert_dbc_message or delete_dbc_signal, but the resource focus is clear enough for selection.

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 explicit when-to-use or when-not-to-use guidance. The only conditional guidance is that auto_pack=True finds the first free bit block, with no mention of alternatives, prerequisites, or when dry_run should be used.

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