Build KurrentDB projections without guessing how they’ll run in production. Projections are server-side JavaScript that turn your events into running totals, derived streams, and read models. Because they run inside the database, they’re hard to develop, harder to debug, and risky to change once live. gaffer brings that runtime to your machine: scaffold, debug, and test locally, then deploy and see exactly what changes before it applies. The engine you develop against is the one KurrentDB runs, so what you debug is what ships.

Install the CLI

npm install -g @kurrent/gaffer

Requires Node.js 22 or later.

Add the VS Code extension

VS Code MarketplaceOpen VSX

Or wire any LSP or DAP aware editor to gaffer.

Connect an AI assistant

Install the gaffer CLI and register its MCP server, following https://gaffer.kurrent.io/install.txt

Paste into Claude Code, Cursor, or any MCP client.

Get startedWrite your first projection, step through it in the debugger, and deploy it to a server.

TestingDrive projections from Vitest, Jest, or Mocha. No database, no flakiness.

CLIScaffold, run, debug, and deploy from your terminal, then track status, drift, and history.

VS Code extensionRun and debug from CodeLens, see deploy status inline, get projection-API autocomplete.

AI assistantsConnect Claude Code, Cursor, Continue, or Claude Desktop to gaffer over MCP.