csvto

CSV, JSON and Excel conversion that runs where your data already is.

• csvto-mcp — an MCP server. Point your AI assistant at a file path; it converts locally and writes the result beside it. Nothing is uploaded, and file contents never pass through the model's context.
• @csvto/core — the conversion engine. No DOM, no fs, no network, so the same tested code runs in a browser, in a local MCP process, or on a server.

The same engine powers the browser tools at csvtosite.com, where conversion happens client-side and files are likewise never uploaded.

Install the MCP server

claude mcp add csvto -- npx -y csvto-mcp

Or in any MCP client's config:

{
  "mcpServers": {
    "csvto": { "command": "npx", "args": ["-y", "csvto-mcp"] }
  }
}

Requires Node 18+. Full tool list and behaviour: packages/mcp/README.md.

Types are inferred per column, not per cell

This is the part that matters, and where most converters quietly corrupt data. A column converts to numbers only if every value in it survives the round trip exactly. If one value would change, the whole column stays text:

• 01234 keeps its leading zero instead of becoming 1234
• A 16-digit account number stays itself instead of becoming 1.23457E+14
• 1250.50 keeps its trailing zero instead of becoming 1250.5
• A column never ends up as a mix of numbers and strings

Verified in tests: 01234 survives a CSV → xlsx → CSV round trip intact.

Develop

npm install
npm test          # 49 tests
npm run build

packages/core must stay environment-free — no window, no fs, no fetch. That constraint is what lets one tested engine serve every surface.

Licence

MIT