RFCXML MCP Server


日本語版 README

A Model Context Protocol (MCP) server for structured understanding of RFC documents.

Purpose

Unlike existing text-based RFC MCP servers, this server leverages the semantic structure of RFCXML to enable:

- Normative requirements extraction (MUST/SHOULD/MAY) with structured output
- RFC dependency graph construction
- Definition scope management
- Implementation checklist generation

Architecture

``
┌─────────────────────────┐
│ Markdown / PDF │ Display & Sharing
├─────────────────────────┤
│ Translation │ Explanation & Verification
├─────────────────────────┤
│ RFCXML MCP │ Common Understanding for AI & Humans
├─────────────────────────┤
│ RFCXML │ Single Source of Truth
└─────────────────────────┘
`

Comparison with Existing MCPs

| Feature | Existing mcp-rfc | RFCXML MCP |
| ------------------------------- | ---------------- | -------------------- |
| RFC text retrieval | ✅ | ✅ |
| Section extraction | ✅ (text-based) | ✅ (structure-based) |
| MUST/SHOULD/MAY extraction | ❌ | ✅ |
| Condition/exception structuring | ❌ | ✅ |
| RFC dependency graph | ❌ | ✅ |
| Definition scope management | ❌ | ✅ |
| Implementation checklist | ❌ | ✅ |

Quick Start

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Add the following to your MCP configuration file:

`json
{
"mcpServers": {
"rfcxml": {
"command": "npx",
"args": ["-y", "@shuji-bonji/rfcxml-mcp"]
}
}
}
`

Configuration file locations:

- Claude Desktop (macOS): ~/Library/Application Support/Claude/claude_desktop_config.json
- Claude Desktop (Windows): %APPDATA%\Claude\claude_desktop_config.json
- Claude Code: .claude/settings.json or use claude settings command

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For global installation:

`bash
npm install -g @shuji-bonji/rfcxml-mcp

MCP configuration


{
"mcpServers": {
"rfcxml": {
"command": "rfcxml-mcp"
}
}
}
`

Available Tools

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- get_rfc_structure - Get section hierarchy and metadata
- get_requirements - Extract normative requirements (MUST/SHOULD/MAY) with structure
- get_definitions - Get term definitions and their scope

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- get_rfc_dependencies - Get referenced RFCs (normative/informative)
- get_related_sections - Get related sections within the same RFC

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- validate_statement - Verify if a statement complies with RFC requirements
- generate_checklist - Generate implementation checklist

Legacy RFC Support

RFCs published after RFC 8650 (December 2019) are available in official RFCXML v3 format. Earlier RFCs may not have XML available.

This server includes automatic fallback functionality - when XML is unavailable, it parses the text format instead.

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All responses include source information:

`json
{
"rfc": 6455,
"sections": [...],
"_source": "text",
"_sourceNote": "⚠️ Parsed from text format. Accuracy may be lower."
}
`

| _source | Description |
| --------- | ---------------------------------- |
| xml | Parsed from RFCXML (high accuracy) |
| text | Parsed from text (medium accuracy) |

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| RFC | Format | Notes |
| --------------- | ------ | -------------------------- |
| RFC 8650+ | XML | Official RFCXML v3 support |
| Before RFC 8650 | Text | Automatic fallback |

Output Samples

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`json
{
"metadata": {
"title": "Transmission Control Protocol (TCP)",
"docName": "draft-ietf-tcpm-rfc793bis-28",
"number": 9293
},
"sections": [
{
"number": "section-1",
"title": "Purpose and Scope"
},
{
"number": "section-3",
"title": "Functional Specification",
"subsections": [
{ "number": "section-3.1", "title": "Header Format" },
{
"number": "section-3.5",
"title": "Establishing a Connection",
"subsections": [
{ "number": "section-3.5.1", "title": "Half-Open Connections and Other Anomalies" },
{ "number": "section-3.5.2", "title": "Reset Generation" }
]
}
]
}
],
"referenceCount": { "normative": 15, "informative": 85 },
"_source": "xml"
}
`

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`json
{
"rfc": 9293,
"filter": { "level": "MUST" },
"stats": { "total": 53, "byLevel": { "MUST": 53 } },
"requirements": [
{
"id": "R-section-3.5-5",
"level": "MUST",
"text": "A TCP implementation support simultaneous open attempts (MUST-10).",
"section": "section-3.5",
"sectionTitle": "Establishing a Connection"
},
{
"id": "R-section-3.7.1-9",
"level": "MUST",
"text": "TCP endpoints implement both sending and receiving the MSS Option (MUST-14).",
"section": "section-3.7.1",
"sectionTitle": "Maximum Segment Size Option"
}
],
"_source": "xml"
}
`

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`json
{
"rfc": 9293,
"normative": [
{ "rfcNumber": 791, "title": "Internet Protocol", "anchor": "RFC0791" },
{ "rfcNumber": 2119, "title": "Key words for use in RFCs to Indicate Requirement Levels" },
{ "rfcNumber": 5681, "title": "TCP Congestion Control" }
],
"informative": [
{ "rfcNumber": 793, "title": "Transmission Control Protocol" },
{ "rfcNumber": 1122, "title": "Requirements for Internet Hosts - Communication Layers" }
],
"_source": "xml"
}
`

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`markdown


RFC 9293 Implementation Checklist

Transmission Control Protocol (TCP)

Role: Client

Required (MUST / REQUIRED / SHALL)

- [ ] A TCP implementation support simultaneous open attempts (MUST-10). (section-3.5)
- [ ] TCP endpoints implement both sending and receiving the MSS Option (MUST-14). (section-3.7.1)
- [ ] The RTO be computed according to the algorithm in, including Karn's algorithm (MUST-18). (section-3.8.1)

Optional (MAY / OPTIONAL)

- [ ] Implementers include "keep-alives" in their TCP implementations (MAY-5). (section-3.8.4)
`

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`json
{
"metadata": {
"title": "The WebSocket Protocol",
"number": 6455
},
"sections": [
{ "number": "1", "title": "Introduction" },
{ "number": "5", "title": "Data Framing" }
],
"_source": "text",
"_sourceNote": "⚠️ Parsed from text format. Accuracy may be lower."
}
`

Examples

See the examples/ directory for complete checklist samples:

| RFC | Protocol | Source |
| ----------------------------------------------------- | --------- | --------------- |
| RFC 6455 | WebSocket | Text (fallback) |
| RFC 9293 | TCP | RFCXML |
| RFC 7540 | HTTP/2 | Text (fallback) |

Example prompt for Claude:

`
Generate an implementation checklist for RFC 9293 (TCP).
`

Internal Architecture

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`
src/
├── index.ts # MCP server entry point
├── config.ts # Centralized configuration
├── constants.ts # BCP 14 keyword definitions
├── services/
│ ├── rfc-fetcher.ts # RFC fetching (parallel)
│ ├── rfcxml-parser.ts # RFCXML parser
│ ├── rfc-text-parser.ts # Text fallback parser
│ └── checklist-generator.ts # Checklist generation service
├── tools/
│ ├── definitions.ts # MCP tool definitions
│ └── handlers.ts # Tool handlers
├── types/
│ └── index.ts # Type definitions
└── utils/
├── cache.ts # LRU cache
├── fetch.ts # Parallel fetch utility
├── requirement-extractor.ts # Shared requirement extraction
├── section.ts # Section search utilities
├── text.ts # Text processing utility
└── validation.ts # Input validation
`

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Sends parallel requests to multiple sources (RFC Editor, IETF Tools, Datatracker) and uses the first successful response:

`
┌─────────────────┐
│ fetchRFCXML() │
└────────┬────────┘
│ Parallel requests
┌────┴────┬────────────┐
▼ ▼ ▼
┌────────┐ ┌────────┐ ┌────────┐
│RFC │ │IETF │ │Data- │
│Editor │ │Tools │ │tracker │
└────┬───┘ └────┬───┘ └────┬───┘
│ │ │
└────┬─────┴──────────┘
│ Promise.any (first success)
▼
┌───────────┐
│ Successful│ → Cancel other requests via AbortController
│ Response │
└───────────┘
`

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LRU (Least Recently Used) cache with memory limits:

| Cache | Max Entries | Content |
| -------------- | ----------- | ---------------- |
| XML Cache | 20 | Raw RFCXML |
| Text Cache | 20 | Raw text |
| Metadata Cache | 100 | RFC metadata |
| Parse Cache | 50 | Parsed structure |

Development

`bash


Install dependencies

npm install

Development mode

npm run dev

Build

npm run build

Test

npm test

Lint

npm run lint

Format

npm run format
``

License

MIT

Related Projects

- mjpitz/mcp-rfc - Text-based RFC MCP
- ietf-tools/RFCXML - RFCXML schema
- xml2rfc - IETF official tool