📦 mcp-server-taxcode

Enterprise-grade Model Context Protocol (MCP) server for Federal, Territorial, and Multi-State Tax Law.
Reference statutory catalog covering United States Federal (IRC/CFR), Puerto Rico (Act 60/Ley 1), and all 50 US States + District of Columbia with computational residency and capital gains models.

🏗️ Architecture: FastMCP 4 Server Composition

graph TD
    Client["AI Agent / MCP Host<br>(Claude, Cursor, Antigravity, Snowflake Cortex)"]
    Gateway["FastMCP Root Gateway<br>(stdio / streamable-http)"]
    ParentMW["Parent Middleware<br>(Audit Logging, Timing, Secret Redaction, ReadOnly Gate)"]
    SysSub["System Sub-server (mount: 'system')<br>• system_get_health_status<br>• taxcode://system/reference/capabilities"]
    StatSub["Statutes Sub-server (mount: 'statutes')<br>• statutes_lookup_statute<br>• statutes_search_tax_code<br>• statutes_list_publications"]
    CompSub["Compliance Sub-server (mount: 'compliance')<br>• compliance_evaluate_pr_bona_fide_residency<br>• compliance_calculate_built_in_gain_sourcing<br>• compliance_evaluate_georgia_residency<br>• compliance_evaluate_state_residency"]
    DuckDB["DuckDB In-Memory & File Engine<br>(106 Statutes, 12 Publications, Full-Text Search, Temporal Versions)"]

    Client <-->|"JSON-RPC (tools/list, tools/call)"| Gateway
    Gateway --> ParentMW
    ParentMW --> SysSub
    ParentMW --> StatSub
    ParentMW --> CompSub
    StatSub <-->|"Point-in-Time & Full-Text Queries"| DuckDB
    CompSub <-->|"Deterministic Statutory Calculations"| DuckDB

🚀 Key Features

• Authoritative Multi-Jurisdiction Statutory Catalog:
  • Federal (US): IRC § 933, § 937, § 865, 26 CFR § 1.937-1/2.
  • Puerto Rico (PR): Act 60-2019 (Resident Individual Investors & Export Services), Ley 1-2011, Act 22-2012 predecessor versions, and administrative circulars (CC RI 21-10, DA 23-04, CC RI 26-13).
  • All 50 US States + District of Columbia: Comprehensive statutory definitions and tax computations covering no-income-tax states (AK, FL, NV, NH, SD, TN, TX, WA, WY), flat-tax regimes (AZ, CO, GA, ID, IL, IN, IA, KS, KY, MI, MS, NC, PA, UT), and graduated/surtax jurisdictions (AL, AR, CA, CT, DE, DC, HI, LA, ME, MD, MA, MN, MO, MT, NE, NJ, NM, NY, ND, OH, OK, OR, RI, SC, VT, VA, WV, WI) including Convenience of the Employer rules (NY, PA, NJ, CT, DE, NE) and local piggyback taxes (MD, IN, OH, NY).
• Temporal Statutory Versioning: Point-in-time statutory lookup with superseded_year filtering and descending historical ordering (tax_year parameter).
• Deterministic Compliance Engines:
  • evaluate_pr_bona_fide_residency: Evaluates IRC § 937 presence (183-day, 549-day 3-year, 90-day US), tax home, and closer connection tests.
  • calculate_built_in_gain_sourcing: Allocates Section 937 / Act 60 capital gains across pre-move and post-move holding periods.
  • evaluate_state_residency: Multi-state statutory presence day-counter, permanent place of abode (PPA), domicile audit risk flags, and tax liability computation across all 50 US states and District of Columbia (51 jurisdictions total).
• Profiles & Opt-in ToolSearch:
  • Domain-mount profiles: full, system, statutes, compliance, readonly.
  • Job-shaped allowlist profiles: researcher (statutes + circulars), advisor (cross-border residency + BIG calculations).
• Zero Tool Bloat: Exactly 8 lean, read-only MCP tools exposed with explicit MCP 2.0 annotations (readOnlyHint=True).

⚙️ Configuration

HTTP transports and authentication

Stdio is the default and needs no token. The HTTP transports follow the MCP guidance that a local server binds only to localhost and authenticates every connection:

• On 127.0.0.1, ::1 or localhost (the --host default is 127.0.0.1), HTTP runs with or without TAXCODE_MCP_AUTH_TOKEN; without it, a warning says requests are not authenticated.
• On any other host (0.0.0.0, ::, a LAN address), the server refuses to start unless TAXCODE_MCP_AUTH_TOKEN is set, or TAXCODE_MCP_ALLOW_UNAUTHENTICATED_BIND=1 accepts an unauthenticated bind (logged as a warning), for example behind a gateway that authenticates for you.
• With a token set, every HTTP request needs Authorization: Bearer <token>; a missing or wrong token gets HTTP 401.
• In the default (stateful) HTTP mode, a session idle for 30 minutes expires: its next request gets HTTP 404 and the client must start a new session. Change this with FastMCP's session_idle_timeout (on http_app()) or FASTMCP_HTTP_SESSION_IDLE_TIMEOUT (seconds, or none to never expire); see the FastMCP 4.1.0 release and #5229.

# Local HTTP, loopback only
taxcode-mcp --transport streamable-http

# Public HTTP with a token
TAXCODE_MCP_AUTH_TOKEN="$(openssl rand -hex 32)" \
  taxcode-mcp --transport streamable-http --host 0.0.0.0 --allowed-host mcp.example.com

Docker

The image's default command is stdio, so it works as a stdio server out of the box:

docker run -i --rm -e TAXCODE_API_KEY=your-api-key ghcr.io/christianclaudio/<name>

To serve Streamable HTTP from the container, bind 0.0.0.0 inside it and pass a token:

docker run --rm -p 8000:8000 \
  -e TAXCODE_API_KEY=your-api-key \
  -e TAXCODE_MCP_AUTH_TOKEN=your-long-random-token \
  ghcr.io/christianclaudio/<name> \
  --transport streamable-http --host 0.0.0.0 --port 8000 --allowed-host mcp.example.com

🔌 Integration Guides for AI Assistants & IDEs

This server works out-of-the-box with all major AI assistants, IDEs, and CLI tools via standard stdio or streamable-http.

The template is not published to PyPI, so these configs run its taxcode-mcp console script from a local clone with uv run --directory. Replace /absolute/path/to/mcp-server-taxcode with the path of your clone. After uv tool install . (or pip install .) puts both console scripts, taxcode-mcp and mcp-server-taxcode (the same server), on your PATH, "command": "taxcode-mcp" with no args works too.

{
  "mcpServers": {
    "taxcode": {
      "command": "uv",
      "args": ["run", "--directory", "/absolute/path/to/mcp-server-taxcode", "taxcode-mcp"],
      "env": {
        "TAXCODE_API_KEY": "your-api-key"
      }
    }
  }
}

claude mcp add taxcode -- uv run --directory /absolute/path/to/mcp-server-taxcode taxcode-mcp

{
  "mcpServers": {
    "taxcode": {
      "command": "uv",
      "args": ["run", "--directory", "/absolute/path/to/mcp-server-taxcode", "taxcode-mcp"],
      "env": {
        "TAXCODE_API_KEY": "your-api-key"
      }
    }
  }
}

{
  "mcpServers": {
    "taxcode": {
      "command": "uv",
      "args": ["run", "--directory", "/absolute/path/to/mcp-server-taxcode", "taxcode-mcp"]
    }
  }
}

{
  "mcpServers": {
    "taxcode": {
      "command": "uv",
      "args": ["run", "--directory", "/absolute/path/to/mcp-server-taxcode", "taxcode-mcp"]
    }
  }
}

{
  "mcpServers": {
    "taxcode": {
      "command": "uv",
      "args": ["run", "--directory", "/absolute/path/to/mcp-server-taxcode", "taxcode-mcp"]
    }
  }
}

📚 Canonical Documentation & Live Doc MCPs

When developing, hardening, or extending MCP servers, consult the official framework and protocol references:

• FastMCP 4 Framework Reference: https://gofastmcp.com/llms.txt — Server composition (mount), hierarchical middleware, transforms (ToolTransform, ToolSearch), lifespans, and in-memory test clients.
• Model Context Protocol Specification: https://modelcontextprotocol.io/llms.txt — Official Spec (2026-07-28), wire-level JSON-RPC schemas, annotations, and transport framing.

Live Documentation MCP Endpoints (SSE / Streamable HTTP)

Connect your AI coding agent directly to live documentation servers:

• FastMCP Documentation Server: https://gofastmcp.com/mcp (Tools: search_fast_mcp, query_docs_filesystem_fast_mcp, submit_feedback)
• Anthropic MCP Documentation Server: https://modelcontextprotocol.io/mcp (Tools: search_model_context_protocol, query_docs_filesystem_model_context_protocol, submit_feedback)

{
  "mcpServers": {
    "fastmcp-docs": { "type": "sse", "url": "https://gofastmcp.com/mcp" },
    "mcp-official-docs": { "type": "sse", "url": "https://modelcontextprotocol.io/mcp" }
  }
}

🏃 Local Development & Verification

# 1. Install dependencies from the lockfile
uv sync --locked --extra dev

# 2. Run unit tests with 100% coverage requirement
uv run pytest

# 3. Static type checks & linting
uv run mypy --strict src/
uv run ruff check .
uv run ruff format --check .

# 4. Tool contract, protocol & drift assertions
uv run python scripts/check_tool_contract.py
uv run python scripts/check_openapi_drift.py
uv run pytest tests/test_protocol.py
uv run pytest tests/test_e2e_live.py -m e2e   # on demand; default CI uses -m 'not e2e'
./scripts/check_conformance.sh

# 5. AI code review gate (CodeRabbit)
coderabbit review --agent --uncommitted

📄 License

Licensed under the Apache License 2.0. See LICENSE for details.