The cosyte MCP server

@cosyte/cli ships a second front door over the same core as the cosyte command: a Model Context Protocol server that lets an LLM/agent parse, validate, inspect, and convert healthcare messages as callable tools. The terminal and the agent share one codebase, one PHI posture, and one set of results: the MCP parse tool returns exactly what cosyte parse returns.

The server is a local stdio subprocess, implicitly trusted by whoever launches it, not a hosted network endpoint. It is stateless per call.

Register it

Add the server to your MCP client's configuration (Claude Desktop, an IDE agent, etc.):

{
  "mcpServers": {
    "cosyte": { "command": "npx", "args": ["-y", "--package", "@cosyte/cli", "cosyte-mcp"] }
  }
}

--package is required here, and the shorter ["-y", "@cosyte/cli", "mcp"] does not work. It fails with could not determine executable to run, because npx picks the executable whose name matches the package name's last segment (cli) and this package ships cosyte and cosyte-mcp. Naming cosyte-mcp explicitly is the supported form.

This registration also requires a version that can be installed at all: 0.0.1 and 0.0.2 cannot be. See If you are on 0.0.1 or 0.0.2. FHIR tools are unavailable from an npm install for a further reason described alongside it.

cosyte mcp starts the stdio server; the standalone cosyte-mcp bin is equivalent.

cosyte mcp        # start the server on stdio (also: cosyte-mcp)

The tools

Tool	What it does
parse	Parse an HL7 v2 / FHIR R4 message to typed JSON (format autodetected).
validate	Validate a message; the result carries the verdict (valid / invalid findings).
inspect	Return a value-free structural summary (type + segment/entry counts).
convert	Convert an HL7 v2 message to a FHIR R4 Bundle via @cosyte/transform.

Every tool takes a content string (the raw message); parse/validate/inspect accept an optional format override.

PHI posture on the agent surface

The value-free discipline is hardened for agents: there is no --unsafe-show-values door over MCP. A tool result carries the requested data (the parsed model, the converted Bundle: the explicit request). A tool error carries only a value-free diagnostic: a stable code and a position, never a name, DOB, MRN, or field value. A parsed-but-invalid validate is a successful call reporting the verdict (not a tool error); only a hard failure (unparseable input, a usage mistake) is flagged as an error.

Isolation

The MCP SDK (@modelcontextprotocol/sdk) is the CLI's only third-party runtime dependency. It is declared optional and loaded only on the MCP path, so a plain cosyte parse never pulls it and the core works with the SDK absent (install with --omit=optional for a minimal footprint). The server surface is also importable programmatically via the @cosyte/cli/mcp subpath.