OpenTax MCP MCP server

OpenTax is a deterministic tax computation engine for AI agents that provides verifiable, statute-cited federal and state tax calculations. It ensures precise returns by using exact arithmetic and rules rather than probabilistic sampling, offering Merkle-rooted proofs for auditability and refusing to guess when inputs fall outside its encoded legal corpus.

Endpoint and access

No sign-in: your client connects and lists tools immediately, with no account or key.

No sign-inEndpoint checked 2026-10-05Operated by Invaro

MCP endpoint (Streamable HTTP)

https://opentax.invaro.ai/mcp

Vendor documentation

What you can do with it

Compute exact federal and state tax liabilities for individuals and businesses
Verify tax claims and facts against encoded legal statutes
Search tax rules and parameters with verbatim source citations
Generate provable audit trails with Merkle-rooted computation proofs

Tools advertised by the last live check:

calculate_tax
calculate_business_tax
calculate_fiduciary_tax
determine_dependent
compute_state_return
compute_return
verify_tax_claim
list_input_facts
explain_rule
find_tax_cliffs
compare_filing_statuses
lookup_tax_parameter
search_tax_rules
verify_fact
is_tipped_occupation

Connect from your client

Each snippet registers the same endpoint; pick the client you use.

This server is operated by the named third party. Listing and endpoint checks are not an endorsement or a security audit. Review the operator's permissions, terms, and data handling before connecting. How listings are checked and corrected.

Claude Code

Run this once in a terminal. It registers a Streamable HTTP server. Use --scope project to write .mcp.json for the repo.

Claude Code configuration

claude mcp add --transport http opentax-mcp https://opentax.invaro.ai/mcp

Codex

Run this once. Codex stores MCP servers in ~/.codex/config.toml (or .codex/config.toml in a trusted project).

Codex configuration

codex mcp add opentax-mcp --url https://opentax.invaro.ai/mcp

Cursor

Merge this server into .cursor/mcp.json in your project, then enable opentax-mcp in your MCP settings.

Cursor configuration

{
  "mcpServers": {
    "opentax-mcp": {
      "url": "https://opentax.invaro.ai/mcp"
    }
  }
}

Cline

Merge this into cline_mcp_settings.json (Cline → MCP Servers → Configure). The type must be streamableHttp for a remote HTTP server.

Cline configuration

{
  "mcpServers": {
    "opentax-mcp": {
      "type": "streamableHttp",
      "url": "https://opentax.invaro.ai/mcp",
      "disabled": false
    }
  }
}

VS Code

Merge this server into .vscode/mcp.json. Use MCP: List Servers to start opentax-mcp and inspect its tools.

VS Code configuration

{
  "servers": {
    "opentax-mcp": {
      "type": "http",
      "url": "https://opentax.invaro.ai/mcp"
    }
  }
}

Gemini CLI

Run this once. It writes .gemini/settings.json in the current project; pass --scope user for ~/.gemini/settings.json.

Gemini CLI configuration

gemini mcp add --transport http opentax-mcp https://opentax.invaro.ai/mcp

Claude Desktop

Merge this into claude_desktop_config.json (macOS: ~/Library/Application Support/Claude/, Windows: %APPDATA%\Claude\), then restart Claude Desktop.

Claude Desktop configuration

{
  "mcpServers": {
    "opentax-mcp": {
      "url": "https://opentax.invaro.ai/mcp"
    }
  }
}

Windsurf

Merge this into ~/.codeium/windsurf/mcp_config.json, then refresh MCP in Cascade. Windsurf remote servers use serverUrl, not url.

Windsurf configuration

{
  "mcpServers": {
    "opentax-mcp": {
      "serverUrl": "https://opentax.invaro.ai/mcp"
    }
  }
}

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