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why_wont_it_arm

Decode iNAV arming-prevention flags to diagnose why a flight controller won't arm, revealing plain-English causes and concrete fixes.

Instructions

Decode the FC's arming-prevention flags into plain English.

This is the #1 question from new iNAV users. Each set bit is mapped to:

A flag name
A plain-language reason
A concrete fix

Also checks whether ARM mode is assigned to a switch.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "why_wont_it_arm"
  }
}

Input Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.3.5Aug 2, 2026

TDQS

A3.9/5.0

Behavior3/5

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

With no annotations provided, the description carries the full burden of transparency. It clearly explains what the tool does (decodes flags, checks ARM mode) and the output structure (name, reason, fix), but does not explicitly state that the operation is read-only or whether a connection is required. For a diagnostic tool, this is a minor gap but not a contradiction.

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 main purpose in the first sentence. The sentence about it being the #1 question adds context but is somewhat optional; still, the overall length is appropriate and efficient.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a zero-parameter tool with no output schema, the description adequately covers what the tool does and what the user can expect (flag name, reason, fix, ARM mode check). It lacks mention of prerequisites like a live connection, but given the simplicity, the description is sufficiently complete.

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

Parameters4/5

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

The tool has zero parameters, so the schema is trivially complete. According to the rubric, a baseline of 4 is applied for 0 params. The description adds no parameter details because there are none to describe.

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 'Decode' with a clear resource 'FC's arming-prevention flags' and explains the output in plain English. It distinguishes itself from sibling tools by focusing on arming issues, stating each set bit is mapped to a name, reason, and fix, plus checking ARM mode switch assignment.

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

Usage Guidelines3/5

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

The description implies a clear use case ('the #1 question from new iNAV users' when a craft won't arm) but does not explicitly contrast with alternative tools like 'diagnose' or 'get_status'. It lacks explicit when-not-to-use guidance or mention of prerequisites such as an active FC connection.

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