MDA Open Spec — a Markdown superset for agent-facing documents. One .mda source compiles to drop-in SKILL.md, AGENTS.md, MCP-SERVER.md, and CLAUDE.md. JSON Schema validated, with typed dependency graph, footnote relationships, and Sigstore-anchored signatures. For agentskills.io and AAIF runtimes.
> A Markdown superset for agent-facing documents. **One source, many targets** — compile into the `.md` files every major agent runtime already loads. **Tamper-evident at load** — every artifact carries a reproducible content digest, and signed artifacts carry Sigstore-anchored signatures, so neither the agent loading the doc nor the human reviewing it has to trust an unsigned blob.