Parse XML to JSON and serialize JSON back to XML via @mukundakatta/xml-mcp (npx)

Recipe: XML ↔ JSON via @mukundakatta/xml-mcp

Server

• Package: @mukundakatta/xml-mcp (npm, v0.1.0)
• Launch: npx @mukundakatta/xml-mcp (stdio, NDJSON framing)
• Engine: fast-xml-parser — attributes via @_ prefix, mixed content via #text
• Auth: none
• Tools: to_json (XML string → JSON), to_xml (JSON object → XML string)

Tool schemas

to_json — { xml: string } → returns JSON with @_-prefixed attribute keys, #text for text-alongside-attributes to_xml — { value: object } → returns well-formed XML; @_-prefixed keys become element attributes, arrays become repeated elements

Gotchas

• MCP SDK 1.29.0 uses NDJSON framing (newline-delimited JSON), NOT Content-Length
• On macOS, the import.meta.url entry-point guard fails with /tmp paths — use realpath to resolve /private/tmp/... before spawning
• to_xml parameter is value (object), NOT json (string) — pass the parsed object directly
• Numeric-looking strings (<year>1925</year>) are parsed as numbers by default (year: 1925)

Verified trace

to_json — XML with attributes and mixed content:

→ {"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"to_json","arguments":{"xml":"<bookstore><book category=\"fiction\"><title lang=\"en\">The Great Gatsby</title><author>F. Scott Fitzgerald</author><year>1925</year><price>10.99</price></book><book category=\"non-fiction\"><title lang=\"en\">Sapiens</title><author>Yuval Noah Harari</author><year>2011</year><price>14.99</price></book></bookstore>"}}}

← {"result":{"content":[{"type":"text","text":"{\"value\":{\"bookstore\":{\"book\":[{\"title\":{\"#text\":\"The Great Gatsby\",\"@_lang\":\"en\"},\"author\":\"F. Scott Fitzgerald\",\"year\":1925,\"price\":10.99,\"@_category\":\"fiction\"},{\"title\":{\"#text\":\"Sapiens\",\"@_lang\":\"en\"},\"author\":\"Yuval Noah Harari\",\"year\":2011,\"price\":14.99,\"@_category\":\"non-fiction\"}]}}}"}]},"jsonrpc":"2.0","id":3}

to_xml — JSON with @_ attributes and arrays:

→ {"jsonrpc":"2.0","id":4,"method":"tools/call","params":{"name":"to_xml","arguments":{"value":{"person":{"@_id":"42","name":"Ada Lovelace","role":"mathematician","contributions":{"item":["analytical engine","first algorithm"]}}}}}}

← {"result":{"content":[{"type":"text","text":"<person id=\"42\">\n  <name>Ada Lovelace</name>\n  <role>mathematician</role>\n  <contributions>\n    <item>analytical engine</item>\n    <item>first algorithm</item>\n  </contributions>\n</person>\n"}]},"jsonrpc":"2.0","id":4}

Both tools respond in under 5ms after server warm-up. Total handshake (init → tools/list → 2 tool calls) completed in ~5.8s including Node.js startup.