The OOXML spec, explained by people who actually implemented it.

What is this?

An interactive reference for ECMA-376 (Office Open XML) built by the SuperDoc — DOCX editing and tooling team. Every page combines XML structure, live rendered previews, and implementation notes that tell you what the spec doesn't.

• Live previews — Edit XML and see it render in real-time. Every example is a working document.
• Implementation notes — Where Word diverges from the spec, what will break your code, and what to do about it.
• Semantic spec search — 18,000+ spec chunks searchable by meaning via MCP server.

Why?

The ECMA-376 spec is 5,000+ pages and it lies. Word's actual behavior diverges from the standard in ways you only discover by building against it. The knowledge to implement OOXML correctly is locked inside a handful of companies that have no incentive to share it.

We faced this at SuperDoc — building a document engine on native OOXML with no roadmap beyond an unreliable spec. We wrote down everything we learned and made it public. No one should have to reverse-engineer Word alone.

MCP Server

Search the ECMA-376 spec with AI. Ask questions in natural language, get answers grounded in the actual specification.

claude mcp add --transport http ecma-spec https://api.ooxml.dev/mcp

Works with Claude Code, Cursor, and any MCP-compatible client. Three tools: search_ecma_spec (semantic search), get_section (by ID), and list_parts (browse structure).

Development

bun install    # Install dependencies
bun dev        # Dev server at http://localhost:5173
bun run build  # Production build

Contributing

Contributions welcome. Add implementation notes, fix examples, or improve the reference.

License

MIT

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Built by 🦋 SuperDoc — DOCX editing and tooling