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1040kit

1040kit

by triple-rainbow
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

1040kit

Free AI tax software that runs on your computer. Your AI assistant (Claude Code, Codex, and soon Claude Desktop and ChatGPT) prepares your US federal return with 1040kit: W-2 and 1099 income, filed by printing and mailing it or by entering it in IRS Free File Fillable Forms. Your documents and your return never leave your computer.

1040kit is not tax advice. You review and sign your own return.

To install it, see docs/install.md. What it computes, flags or doesn't handle yet: docs/coverage.md. Website: https://1040kit.com

What's here

Path

What

packages/engine

@1040kit/engine: the deterministic federal tax engine (TY2025, TY2026)

packages/mcp

1040kit: the MCP server the AI assistant talks to (documents, interview, forms, filing)

plugins/claude-code, plugins/codex

The skills (do-my-taxes, explain-my-return) and install config

plugins/dev

A launcher for running the MCP server from this repo

.claude-plugin/marketplace.json

The Claude Code plugin marketplace

The engine is pure TypeScript with no dependencies: every number it produces is a traced node with its inputs and an IRS citation. The MCP server is the only part that touches files, and the skills tell the assistant how to run the interview.

Related MCP server: OpenAccountants

Local testing

Requires Node.js 20+ and pnpm.

pnpm install

Run the test suites:

pnpm test

Start the MCP server by hand (it speaks MCP over stdin/stdout, so it waits silently):

./plugins/dev/1040kit-dev.sh

The launcher runs packages/mcp/src/bin.ts with tsx, no build. Unless you set KIT1040_HOME and KIT1040_CONFIG_DIR, workspaces and keys go to the gitignored sandbox .dev/taxes and .dev/config in this repo, so tests never touch ~/Taxes.

Claude Code, with the skills and the local server. From the repo root:

claude --plugin-dir plugins/claude-code --mcp-config plugins/dev/mcp.json --strict-mcp-config

--strict-mcp-config skips the plugin's own npx -y 1040kit server, which would download the npm package. Then say "do my taxes". Put synthetic test documents (no real SSNs) in the inbox folder the assistant gives you.

Codex, with the local server. Codex starts servers from any folder, so use the absolute path:

codex mcp add 1040kit-dev -- "$PWD/plugins/dev/1040kit-dev.sh"
mkdir -p ~/.codex/skills && cp -RL plugins/codex/skills/do-my-taxes plugins/codex/skills/explain-my-return ~/.codex/skills/

Remove it afterwards with codex mcp remove 1040kit-dev.

The interview widget. interview_next shows its questions as a card with answer chips in hosts that support MCP Apps. To try the card in a browser without a host:

pnpm --filter 1040kit widget:harness
python3 -m http.server 4310 -d packages/mcp/.widget-harness

Then open http://localhost:4310.

Note: 1040kit@0.0.1 on npm today is a placeholder (README only, no server), so the npx install commands don't work yet.

License

AGPL-3.0. Copyright (C) 2026 Triple Rainbow.

This server cannot be deployed

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Maintenance

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