Arc & Ledger Tax Reference

Arc & Ledger Tax Help MCP server

A public remote Model Context Protocol server for general US tax information, screening tools, estimates, and firm-specific service tools. It runs as a stateless Cloudflare Worker and requires no Arc & Ledger account or authentication.

The project exposes two surfaces:

Edition	Endpoint	Scope
Complete server	https://mcp.arcandledger.com/mcp	21 tools, 12 prompts, 4 read-only resources, and 4 optional ChatGPT cards. Some results include first-party firm or service links.
Directory edition	https://mcp.arcandledger.com/directory/mcp	13 reviewed educational tools. No prompts, resources, cards, firm pricing, service matching, booking, payment, upload, purchase, or promotional handoff.

• Complete docs: https://www.arcandledger.com/mcp/
• Directory docs: https://www.arcandledger.com/mcp/directory/
• MCP privacy policy: https://www.arcandledger.com/mcp/privacy/
• Support: https://www.arcandledger.com/mcp/support/

Every result is general information, not tax advice, and creates no practitioner-client relationship. The tools do not file, transmit, sign, certify, authorize payment, or access a taxpayer account.

Connect

No API key, OAuth flow, or Arc & Ledger account is required. For the reviewed educational surface, use:

https://mcp.arcandledger.com/directory/mcp

For local Claude Code testing:

claude mcp add --transport http arc-ledger-tax-reference https://mcp.arcandledger.com/directory/mcp

The complete endpoint remains available to users who intentionally want the firm-specific public tools documented on the main MCP page.

Directory tool set

The directory edition is the surface proposed for the OpenAI Plugins Directory and Anthropic Software Directory.

Tool	General purpose
decode_irs_notice	Explain a supported IRS notice code and usual response path.
check_resolution_options	Screen general IRS payment and collection alternatives.
estimate_irs_penalty	Estimate selected federal late-filing, late-payment, and underpayment amounts.
explain_tax_document	Explain the purpose and common fields of a named US tax document.
deadline_calendar	Return common federal filing and payment dates.
check_fbar_fatca	Screen general FBAR and Form 8938 thresholds.
check_treaty_withholding	Explain general withholding rules and supported US-Turkey treaty rates.
check_itin_eligibility	Screen general ITIN reason categories without treating entity ownership as automatic eligibility.
check_5472_obligation	Screen common Form 5472 triggers.
estimate_quarterly_taxes	Estimate federal quarterly payments and show assumptions.
estimate_accountable_plan	Estimate potentially reimbursable expenses, including split 2026 mileage rates.
estimate_augusta_rule	Screen the fewer-than-15-days home-rental rule and calculate conditional amounts.
estimate_rental_income	Estimate a basic rental-income result and modeled limitations.

Each directory result:

• cites an official IRS or FinCEN page;
• includes a shared general-information limitation;
• tells the calling model to preserve exact returned figures and dates;
• contains no Arc & Ledger service, contact, booking, payment, or upload link.

The directory edition intentionally excludes firm quotations, consultations, document collection, service matching, formation-state comparisons, sales-tax nexus screens, and reasonable-compensation ranges. Those tools either have a commercial purpose, rely on changing state data, or need more professional judgment than a short deterministic screen should imply.

Privacy and safety

• Tool inputs are processed in memory to answer the request.
• The Worker writes no tool-call inputs, outputs, tool names, or per-call analytics to application logs.
• Cloudflare Worker observability is disabled.
• The server uses the request's network address temporarily as a rate-limit key. It is not written to application storage or paired with the tool body.
• There is no MCP request database, user history, tax-return store, or document upload surface.
• Users are instructed not to send SSNs, ITINs, EINs, tax account numbers, bank details, passwords, or documents.
• All tools carry readOnlyHint: true, destructiveHint: false, and an explicit openWorldHint.

Cloudflare still processes ordinary request metadata as the infrastructure provider. The public privacy policy describes that boundary.

Claude plugin

plugin/ is a Claude plugin bundle that points to the directory endpoint and adds two procedural Skills:

• respond-to-your-irs-notice
• resolve-back-taxes

The Skills use only tools available on the directory edition. They lead with deadlines and filing-compliance gates, label estimates, retain official source links, request no sensitive identifiers or documents, and do not promote or sell a firm service.

The repository marketplace manifest lives at .claude-plugin/marketplace.json.

/plugin marketplace add Bgenc48/arc-ledger-mcp
/plugin install arc-ledger-irs@arc-ledger

Architecture

• Stateless Streamable HTTP JSON-RPC handler, with no sessions or Durable Objects.
• Official @modelcontextprotocol/sdk protocol types and zod input schemas.
• Two registries: the complete server in src/registry.ts and the restricted directory surface in src/directory.ts.
• A 65,536-byte request-body cap, JSON content-type enforcement, batch limits, CORS handling, and per-network-address rate limiting.
• Per-tool kill switch through DISABLED_TOOLS.
• Version, tax-year, and active-tool counts exposed by GET /version.
• Apps SDK widgets are bound only on the complete server. The directory edition exposes standard MCP results with no UI resource.

Routes

Route	Purpose
POST /mcp	Complete MCP surface.
POST /directory/mcp	Restricted directory MCP surface.
GET /healthz	Liveness.
GET /version	Version, tax year, tool counts, and directory endpoint.
GET /.well-known/mcp-registry-auth	MCP Registry domain proof.
GET /.well-known/openai-apps-challenge	Exact OpenAI domain challenge when configured.

Commands

npm ci
npm run typecheck
npm test
npm run dev
npm run bundle-check
npm run gen:products
node scripts/gen-examples.mjs

npm run bundle-check runs a Cloudflare Worker dry deployment. The bundled workerd binary does not support every local Windows ARM64 environment, so the hosted CI result is the release gate when that platform limitation occurs.

Layout

src/
  index.ts            Worker routes, request limits, and registry selection
  registry.ts         Complete 21-tool and 12-prompt registry
  directory.ts        Restricted 13-tool directory registry and output scrubber
  pricing.ts          Adapter over the published pricing data source
  rates.ts            Adapter over reviewed tax-year constants
  resources.ts        Complete-server read-only resources
  lib/                MCP, response, rate-limit, tax, date, and schema helpers
  tools/              One module per tool
  ui/                 Complete-server Apps SDK widgets
plugin/               Claude plugin bundle
test/                 Protocol, HTTP, tax, directory, privacy, and governance tests

License

Source-available for transparency and directory review. All rights reserved; see LICENSE.