Arc & Ledger Tax Tools

A public, no-auth remote MCP server that exposes Arc & Ledger's free tax calculators and intake tools inside AI assistants (Claude, ChatGPT, and any MCP-capable client). Runs as a stateless Cloudflare Worker; nothing is filed, purchased, or stored. Every answer is general information (not tax advice) with an optional handoff to an Enrolled Agent enrolled to practice before the IRS.

• Endpoint: https://mcp.arcandledger.com/mcp (Streamable HTTP)
• Docs: https://www.arcandledger.com/mcp
• Privacy: https://www.arcandledger.com/mcp/privacy

Connect it

No API key, no account, no OAuth: paste the endpoint URL and go.

• Claude (web and desktop): Settings -> Connectors -> Add custom connector -> https://mcp.arcandledger.com/mcp (no authentication).
• Claude Code: claude mcp add --transport http arc-ledger https://mcp.arcandledger.com/mcp
• ChatGPT (developer mode): Settings -> Apps & Connectors -> enable developer mode -> create a connector with the same URL, authentication "None". Two tools additionally render in-chat cards (IRS notice decoder and formation-state comparison) on surfaces that support the Apps SDK.

Menu names change between releases; the constant part is the endpoint URL and "no auth".

Tools

All 19 tools are read-only and deterministic: the same inputs always produce the same answer.

Tool	Purpose
decode_irs_notice	Explain an IRS notice (28 covered codes), its deadline, and what to do.
explain_tax_document	Explain a tax form you received (W-2, 1099 family, K-1, 1042-S, 1095-A...): key boxes, where it goes on the return, what to check, and what to do if it is wrong or missing.
check_fbar_fatca	FBAR / Form 8938 obligations, thresholds, catch-up.
compare_llc_scorp	SE tax vs salary+distribution, CA franchise, break-even.
estimate_quarterly_taxes	Federal + CA quarterly estimates with safe harbor.
estimate_rental_income	Net rental income, depreciation, passive-loss allowance, 14-day rule.
deadline_calendar	US filing deadlines + penalties for founders (1120/5472, 1040-NR, FBAR, BOI).
check_itin_eligibility	ITIN eligibility, W-7 category, documents; Enrolled Agent prepares the W-7 and represents you.
estimate_irs_penalty	Failure-to-file / failure-to-pay penalties + interest on a balance; abatement.
check_resolution_options	Screens IRS back-tax paths: payment plan, OIC (fit-check only), CNC, penalty abatement + forms.
compare_formation_states	Wyoming vs New Mexico vs Delaware vs California for a US LLC.
check_sales_tax_nexus	Economic + physical (FBA) sales-tax nexus by state.
estimate_reasonable_comp	S-corp reasonable-compensation starting range (facts-and-circumstances caveats included).
estimate_augusta_rule	Renting your home to your business under IRC 280A(g): the 14-day exclusion, documentation, limits.
estimate_accountable_plan	Accountable-plan reimbursement estimate: home office, mileage, cell/internet.
check_treaty_withholding	US withholding for non-US payees: default rates, US-Turkey treaty rates, W-8BEN / W-8BEN-E / W-9 / Form 8233.
get_document_checklist	Documents to gather per engagement (1040, Schedule C, 5472, 1120-S, 1065, FBAR catch-up, ITIN).
get_fee_quote	Published fee range and line items for firm services.
book_consultation	First-party booking link + office identity.

Plus ten prompts (five English, four Turkish, one Spanish): decode_my_irs_notice, explain_my_tax_form, am_i_required_to_file_fbar, should_i_be_an_scorp, settle_my_irs_debt, abd_sirket_vergi_takvimi, bu_vergi_formu_ne, itin_almali_miyim, irs_borc_cozumu, decodificar_mi_aviso_irs.

And four read-only resources (arcledger://office, arcledger://services, arcledger://fee-catalog, arcledger://tool-directory) so an assistant can cite the firm's identity, service directory, and fee catalog directly.

Claude plugin (Skill + Connector)

plugin/ is an installable Claude plugin that bundles the respond-to-your-irs-notice Skill with this MCP server (via .mcp.json), so one install adds both the orchestration methodology and the tools it drives. The marketplace manifest lives at .claude-plugin/marketplace.json:

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

The Skill decodes an IRS notice, leads with the deadline, sizes penalties, screens resolution options, and hands off to an Enrolled Agent. Circular 230 safe: general information only, never a guaranteed IRS outcome.

Design

• Stateless Streamable-HTTP JSON-RPC handler (no sessions, no Durable Objects). Uses the official @modelcontextprotocol/sdk types + zod.
• No hardcoded prices or rates. src/pricing.ts is an adapter over the pricing data module: the single source of truth carrying the same numbers published at arcandledger.com/pricing/. src/rates.ts adapts the 2026 tax constants and adds only server-only pieces documented with their statutory source (safe harbor, CA S-corp rate, Form 8938 matrix, CA 30/40/0/30).
• Shared response envelope: every tool returns the same disclaimer, a first-party source_url, and one first-party next_step handoff. A content-governance test sweeps every rendered output for banned and required strings.
• Privacy: inputs processed in memory; logs carry only tool name, timestamp, and coarse enums (never free text or dollar amounts), retained 30 days.
• Rate limiting: per-IP token bucket (60/min, burst 10) + the native RATE_LIMITER binding when bound.

Endpoints

Route	Purpose
POST /mcp	The MCP endpoint (Streamable HTTP, JSON-RPC).
GET /healthz	Liveness.
GET /version	Server version, price set, tax year, tool/prompt counts.
GET /.well-known/mcp-registry-auth	MCP Registry domain-ownership proof.

Commands

npm ci                 # install (package-lock is authoritative)
npm test               # vitest: protocol, HTTP surface, tool correctness, determinism, schema snapshot, governance
npm run typecheck      # tsc --noEmit (strict)
npm run dev            # wrangler dev (local)
npm run bundle-check   # wrangler deploy --dry-run (proves the worker bundles)
npm run gen:products   # regenerate the products.json feed from the catalog
node scripts/gen-examples.mjs   # regenerate docs/worked-examples.json

Layout

src/
  index.ts            Worker entry: /mcp, /healthz, /version, /.well-known/mcp-registry-auth, CORS, rate limit
  registry.ts         The 19 tools + 10 prompts
  pricing.ts          Adapter over the pricing data module (SSOT for prices)
  rates.ts            Adapter over the 2026 tax constants + server-only tax constants
  resources.ts        The four arcledger:// resources
  lib/                mcp (protocol), response, logging, rateLimit, tax, dates, schemas
  tools/              one file per tool
  ui/                 Apps SDK widgets (IRS notice card, formation-state comparison)
  data/               data modules: IRS notices, tax documents (and, in the public
                      mirror, the vendored pricing / tax-constant / catalog /
                      service-page snapshots)
test/                 vitest suites + the tool input-schema snapshot

License

Source-available: the code is published for transparency and registry review. All rights reserved; see LICENSE.