RCA-MCP Connector

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rca_dtree_start

Launch a guided diagnostic session that asks targeted questions to determine the root cause of equipment faults, supporting both predefined guides and FMEA-generated trees.

Instructions

🌟 Starter+ — Begin an interactive diagnostic session using a decision tree guide. Returns a question — answer with rca_dtree_answer, one call per question, until the session resolves to a diagnosis.

Two modes:

guide_id = → Use a specific json_dtree guide
guide_id = "auto" → Auto-generate tree from FMEA results (requires fmea_result_id pointing to a completed FMEA analysis)

session_id resume behavior (non-obvious): if you pass a session_id that's yours and not yet resolved, this returns its CURRENT question — guide_id/equipment_id/symptom are ignored entirely in that case. If the session_id is missing, already resolved, or belongs to someone else, it's silently treated as if you'd omitted it: a brand-new session starts fresh under that same session_id (or a fresh UUID if you didn't supply one) — you won't get an error, so a typo'd ID quietly starts over rather than resuming.

Args: params (DTreeStartInput): - guide_id: guide UUID or "auto" - equipment_id: equipment being diagnosed - symptom: initial fault description - session_id: optional; see resume behavior above - fmea_result_id: required when guide_id="auto"

Returns: str: JSON with session_id, question, options (yes/no/unknown), progress_pct

Input Schema

TableJSON Schema

Name	Required	Description	Default
`params`	Yes

Output Schema

TableJSON Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv4.1.15Sep 8, 2026
- addedInput schema / $defs / DTreeStartInput / properties / client_id / description
```
Added value: +"Client namespace ID"
```
- addedInput schema / $defs / DTreeStartInput / properties / token / description
```
Added value: +"API key to authenticate this request"
```
Changed1 schema field changedv4.1.14Sep 7, 2026
- addedInput schema / $defs / DTreeStartInput / properties / equipment_id / description
```
Added value: +"Equipment this diagnostic session is for, e.g. 'pump_XR200_unit3'"
```
First observedv4.1.13Jul 27, 2026

TDQS

A4.7/5.0

Behavior5/5

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

The description richly discloses non-obvious behavior beyond the annotations: session_id resume semantics, silent fallback to a new session for missing/resolved/foreign session IDs, ignored parameters during resume, and lack of error on typo'd IDs. This is exactly the kind of behavioral context an agent needs and is not available from the annotations or schema.

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 long but every section earns its place: purpose, mode selection, session resume caveats, parameter list, and return value. The non-obvious session behavior is front-loaded and clearly separated. No filler or redundant restatement of the tool name.

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

Completeness5/5

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

For a session-starting tool with complex mode logic and subtle resume behavior, the description covers all necessary calling conditions, required parameters, response fields, and the follow-up protocol. The output schema further confirms the return structure, and the description explains semantics that the schema cannot convey.

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?

Despite the low schema description coverage signal, the description adds substantial meaning for guide_id, session_id, fmea_result_id, equipment_id, and symptom, including mode-specific requirements and resume behavior. It omits token and client_id, but those are authentication/namespace parameters already described in the schema and are less decision-critical.

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 clearly states a specific action ('Begin an interactive diagnostic session using a decision tree guide') and identifies the expected output and follow-up tool (rca_dtree_answer). It also distinguishes the two modes of operation and is unambiguous against sibling tools like rca_dtree_answer and rca_dtree_generate_from_fmea.

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 gives explicit context for when to use this tool: to start a session, with either a concrete guide_id or auto-generation from completed FMEA results. It also explains the required fmea_result_id for auto mode and describes the resumption behavior. It does not explicitly list conditions for avoiding this tool in favor of a sibling, but the workflow guidance is clear enough.

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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