# easybill MCP Server

An [MCP](https://modelcontextprotocol.io) server for the [easybill REST API](https://www.easybill.de/api/).
Gives any MCP-capable assistant — Claude Code, Claude Desktop, Cursor, VS Code, Windsurf, Zed,
Codex CLI, Gemini CLI, Cline — access to your invoices, customers, article catalogue, payments,
projects and tracked time.

Built on the official [`@modelcontextprotocol/sdk`](https://github.com/modelcontextprotocol/typescript-sdk)
(TypeScript), talking stdio.

- **54 tools** across 12 easybill resources
- **Read-only by default** — create/update/delete tools stay unregistered unless you opt in
- **Workflow-aware** — ships server instructions so the agent resolves the customer before
  writing a document, instead of guessing where to start
- **Fuzzy customer search** the easybill API itself does not offer
- **Self-throttling** to respect easybill's 10–60 requests/minute cap
- **Context-aware responses** — compact field sets, pagination metadata, automatic truncation

---

## Setup

### 1. Get an easybill API key

In easybill: **Einstellungen → App-Center → API**. Create a key and copy it.

### 2. Register it with your client

This is a plain stdio MCP server published on npm, so any MCP client can run it with `npx` —
no clone, no build, no global install:

```bash
npx -y easybill-mcp
```

Configuration is entirely through environment variables (full list under
[Configuration](#configuration)). Two matter now:

- Leave `EASYBILL_ENABLE_WRITES` unset to start **read-only**.
- Set `EASYBILL_RATE_LIMIT_PER_MINUTE` to **10** on easybill's PLUS plan or **60** on BUSINESS.

Most clients use the same JSON shape under an `mcpServers` key:

```json
{
  "mcpServers": {
    "easybill": {
      "command": "npx",
      "args": ["-y", "easybill-mcp"],
      "env": {
        "EASYBILL_API_KEY": "your_api_key_here",
        "EASYBILL_RATE_LIMIT_PER_MINUTE": "10"
      }
    }
  }
}
```

Where that block goes:

| Client | Config location |
|---|---|
| **Claude Desktop** | Settings → Developer → Edit Config, or `~/Library/Application Support/Claude/claude_desktop_config.json` (macOS) · `%APPDATA%\Claude\claude_desktop_config.json` (Windows) |
| **Cursor** | `~/.cursor/mcp.json` (global) or `.cursor/mcp.json` (per project) |
| **Windsurf** | `~/.codeium/windsurf/mcp_config.json` |
| **Cline / Roo Code** | MCP Servers panel → Configure MCP Servers (`cline_mcp_settings.json`) |
| **Gemini CLI** | `~/.gemini/settings.json` |
| **Claude Code** | `claude mcp add`, see below |
| **VS Code / Copilot** | `.vscode/mcp.json`, different key — see below |
| **Zed** | `settings.json` → `context_servers`, see below |
| **Codex CLI** | `~/.codex/config.toml`, TOML instead of JSON — see below |

> **Windows:** if a client fails to start `npx`, use `"command": "cmd"` with
> `"args": ["/c", "npx", "-y", "easybill-mcp"]`.

#### Claude Code

```bash
claude mcp add easybill \
  --env EASYBILL_API_KEY=your_api_key_here \
  --env EASYBILL_RATE_LIMIT_PER_MINUTE=10 \
  -- npx -y easybill-mcp
```

`claude mcp add` does not overwrite an existing entry — to change the environment later,
`claude mcp remove easybill -s local` first, then add it again.

#### VS Code (GitHub Copilot agent mode)

VS Code uses `servers`, not `mcpServers`, and can prompt for the key instead of storing it
in the file. Put this in `.vscode/mcp.json` (workspace) or open **MCP: Open User
Configuration**:

```json
{
  "inputs": [
    { "id": "easybill_key", "type": "promptString", "description": "easybill API key", "password": true }
  ],
  "servers": {
    "easybill": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "easybill-mcp"],
      "env": {
        "EASYBILL_API_KEY": "${input:easybill_key}",
        "EASYBILL_RATE_LIMIT_PER_MINUTE": "10"
      }
    }
  }
}
```

#### Zed

In `settings.json`:

```json
{
  "context_servers": {
    "easybill": {
      "source": "custom",
      "command": "npx",
      "args": ["-y", "easybill-mcp"],
      "env": {
        "EASYBILL_API_KEY": "your_api_key_here",
        "EASYBILL_RATE_LIMIT_PER_MINUTE": "10"
      }
    }
  }
}
```

#### Codex CLI

In `~/.codex/config.toml`:

```toml
[mcp_servers.easybill]
command = "npx"
args = ["-y", "easybill-mcp"]
env = { EASYBILL_API_KEY = "your_api_key_here", EASYBILL_RATE_LIMIT_PER_MINUTE = "10" }
```

#### Hosted clients that only speak remote MCP

Some clients (ChatGPT connectors, hosted agent platforms) accept only HTTP/SSE endpoints, not
stdio. Bridge it locally:

```bash
npx -y supergateway --stdio "npx -y easybill-mcp"
```

Only do this if you understand the exposure: anything that reaches that endpoint reaches your
accounting data. Keep it bound to localhost or behind a tunnel with authentication, and never
run the bridge with writes enabled unless the endpoint is protected.

### 3. Verify the connection

Ask the assistant to call `easybill_get_server_info`. It reports the mode, the limits and
whether easybill accepted the credentials:

```json
{
  "server_version": "1.0.1",
  "writes_enabled": false,
  "tools_registered": { "read_only": 28, "write": 0, "withheld_because_writes_disabled": 26 },
  "rate_limit_per_minute": 10,
  "connection": "ok — credentials accepted by easybill"
}
```

### 4. Enable writes, once you trust it

Add `EASYBILL_ENABLE_WRITES=true` to the server's environment:

```bash
claude mcp add easybill \
  --env EASYBILL_API_KEY=your_api_key_here \
  --env EASYBILL_RATE_LIMIT_PER_MINUTE=10 \
  --env EASYBILL_ENABLE_WRITES=true \
  -- npx -y easybill-mcp
```

The 26 write tools are registered at startup, so the change only takes effect once the client
restarts the server process — editing the config in a running session is not enough. Confirm
with `easybill_get_server_info`: `writes_enabled` must read `true`.

---

## Running from a local clone

For development, or to run a version you have not published:

```bash
git clone https://github.com/stack74/easybill-mcp.git
cd easybill-mcp
npm install
npm run build
```

Then point the client at the built entry point instead of `npx` — `"command": "node"`,
`"args": ["/absolute/path/to/easybill-mcp/dist/index.js"]`, same `env` block. Or straight from
GitHub without cloning, which is slower because it compiles TypeScript on install via the
`prepare` script and needs a toolchain:

```bash
npx -y github:stack74/easybill-mcp
```

### Test locally first

Copy `.env.example` to `.env`, put your key in it, then run the read-only self-test:

```bash
cp .env.example .env
$EDITOR .env
npm run smoke
```

It makes five read-only calls and prints what came back:

```
easybill-mcp-server v1.x.y self-test
API: https://api.easybill.de/rest/v1
Throttle: 60 req/min | writes disabled

  OK    Auth check (customer groups): total=2  first=Stammkunden
  OK    Customers: total=42  first=Example GmbH
  OK    Invoices: total=128  first=RE-2026-0001
  OK    Unpaid invoices: total=7  first=RE-2026-0117
  OK    Articles (positions): total=95  first=ART-001

All probes passed. The server is ready to register with an MCP client.
```

(Numbers above are illustrative — you will see your own account's totals.)

On a bad key it fails on the first call and stops, so it never burns your rate limit.

To poke at individual tools interactively:

```bash
npm run inspect     # MCP Inspector, loads .env
```

> **Note:** `.env` is only read by these npm scripts, via Node's `--env-file`. The server
> itself reads plain environment variables — when you register it with an MCP client, pass
> the key through the client's config, not via `.env`.

### Publishing to npm

```bash
npm login                  # once, needs an npmjs.com account
npm run build && npm run smoke
npm publish                # unscoped packages are public by default
```

Verify what ships before you publish — `npm pack --dry-run` lists the tarball contents.
Only `dist/`, `README.md`, `LICENSE` and `package.json` are included; `src/` and `.env`
are not.

For later releases bump the version first (`npm version patch|minor|major`), which also
creates a git tag. npm does not allow republishing an existing version.

---

## Configuration

| Variable | Default | Purpose |
|---|---|---|
| `EASYBILL_API_KEY` | — | **Required.** Your easybill API key. |
| `EASYBILL_ENABLE_WRITES` | *unset* | Set to `true` to register create/update/delete tools. Otherwise read-only. |
| `EASYBILL_RATE_LIMIT_PER_MINUTE` | `60` | Client-side throttle. Use `10` for PLUS, `60` for BUSINESS. |
| `EASYBILL_CHARACTER_LIMIT` | `25000` | Max characters per response before truncation. |
| `EASYBILL_TIMEOUT_MS` | `30000` | HTTP request timeout. |
| `EASYBILL_MAX_RETRIES` | `3` | Retries on HTTP 429 / 5xx. |
| `EASYBILL_BASE_URL` | easybill production | Override for a proxy or test double. |

---

## Tools

### Customer lookup

| Tool | Access |
|---|---|
| `easybill_find_customer` | read — **start here**: fuzzy search by name, email or number |

The easybill API has no full-text search, so this tool tries exact filters first, then pages
the customer list and scores candidates locally. It tolerates legal forms (`GmbH & Co. KG`),
punctuation (`M.B. MUSTERMANN` vs `MB Mustermann`), umlauts and word order.

### Documents — invoices, offers, credit notes, deliveries, orders

| Tool | Access |
|---|---|
| `easybill_list_documents` | read |
| `easybill_get_document` | read |
| `easybill_download_document` | read — saves PDF / ZUGFeRD / XRechnung to disk |
| `easybill_list_document_versions` | read — audit trail |
| `easybill_create_document` | write |
| `easybill_update_document` | write |
| `easybill_complete_document` | write — finalises a draft, assigns the invoice number |
| `easybill_cancel_document` | write — creates a STORNO document |
| `easybill_convert_document` | write — OFFER → INVOICE, INVOICE → DUNNING, … |
| `easybill_send_document` | write — **sends real email / fax / post** |
| `easybill_delete_document` | write, destructive |

### Customers, contacts, groups

`easybill_list_customers`, `easybill_get_customer`, `easybill_create_customer`,
`easybill_update_customer`, `easybill_delete_customer`,
`easybill_list_contacts`, `easybill_get_contact`, `easybill_create_contact`,
`easybill_update_contact`, `easybill_delete_contact`,
`easybill_list_customer_groups`, `easybill_get_customer_group`

### Article catalogue and stock

`easybill_list_positions`, `easybill_get_position`, `easybill_create_position`,
`easybill_update_position`, `easybill_delete_position`,
`easybill_list_stock_entries`, `easybill_get_stock_entry`, `easybill_create_stock_entry`

### Payments

`easybill_list_document_payments`, `easybill_get_document_payment`,
`easybill_create_document_payment`, `easybill_delete_document_payment`

### Projects and time tracking

`easybill_list_projects`, `easybill_get_project`, `easybill_create_project`,
`easybill_update_project`, `easybill_delete_project`,
`easybill_list_time_trackings`, `easybill_get_time_tracking`,
`easybill_create_time_tracking`, `easybill_update_time_tracking`, `easybill_delete_time_tracking`

### Attachments and templates

`easybill_list_attachments`, `easybill_get_attachment`, `easybill_download_attachment`,
`easybill_delete_attachment`, `easybill_list_text_templates`, `easybill_get_text_template`,
`easybill_list_pdf_templates`

### Server

`easybill_get_server_info` — reports mode, limits and whether the credentials work.

---

## Things worth knowing

### The server tells the agent how to sequence work

A plain set of endpoint wrappers leads agents astray. Handed an inbound customer inquiry,
Claude's first instinct was to call `easybill_list_documents` — which cannot answer the actual
first question, *is this company already a customer?*

The server therefore ships MCP **server instructions** (see `src/instructions.ts`) with the
ordering for common tasks, and `easybill_create_document` opens with the same sequence:

```
1. easybill_find_customer     — does the customer exist?
2. easybill_create_customer   — only if not
3. easybill_create_document   — creates a DRAFT
4. review with the user
5. easybill_complete_document — assigns the official number, locks it
6. easybill_send_document     — only when explicitly asked
```

`easybill_list_documents` explicitly says it is *not* the tool for orienting yourself. If you
extend this server, keep that pattern: state prerequisites at the top of the description of
the tool an agent will reach for first.

### All money is in cents

easybill represents every monetary value as an **integer in cents**, even where the API
types it as a float. `1999` means **19.99 EUR**. This is stated in every tool description
that touches an amount, because getting it wrong produces invoices off by 100×.

Times in time tracking (`timer_value`) are in **minutes**.

### Drafts vs. completed documents

`easybill_create_document` produces a **draft**. It has no official document number and can
still be edited. Call `easybill_complete_document` to finalise it — easybill then assigns the
number and locks it.

To void a completed invoice, use `easybill_cancel_document` (which creates a proper STORNO
document), not `easybill_delete_document`. Completed invoices generally cannot be deleted for
legal reasons.

### Rate limits are low

easybill allows **10 requests/minute on PLUS** and **60 on BUSINESS**. The server throttles
itself to `EASYBILL_RATE_LIMIT_PER_MINUTE` and, if a 429 slips through, retries while honouring
`Retry-After`. Set the variable to match your plan — otherwise a broad question that pages
through many documents will stall.

Because of this, prefer narrow filters over paging: `easybill_list_documents` with
`type='INVOICE'` and `paid_at='null'` costs one request, where scanning everything costs dozens.

### Context management

`Document` has 69 fields and `Customer` 79. List tools therefore return a **compact default
field set**, and single-record lookups return everything. Both accept `fields`:

- omit it → compact defaults
- `fields: ["number", "amount"]` → just those (plus `id`)
- `fields: ["all"]` → every field

Responses over `EASYBILL_CHARACTER_LIMIT` are truncated, halving the item count until they
fit, and say so in `truncation_message`.

### No fuzzy customer search

The easybill API has no full-text search. Customer filters match **exact** values (each
accepts several comma-separated). To find a customer by partial name, either use the exact
spelling or page through and match locally.

### Useful filter recipes

| Question | Call |
|---|---|
| Which invoices are unpaid? | `easybill_list_documents` `type='INVOICE'`, `paid_at='null'` |
| Revenue in 2025? | `easybill_list_documents` `type='INVOICE'`, `document_date='2025-01-01,2025-12-31'` |
| One customer's history | `easybill_list_documents` `customer_id=<id>` |
| Only real, non-cancelled invoices | add `is_draft='0'`, `cancel_id='null'` |
| Unbilled tracked time | `easybill_list_time_trackings`, then filter `cleared_at = null` |

---

## Development

```bash
npm run build      # compile to dist/
npm run typecheck  # tsc --noEmit
npm test           # offline suite — 37 tests, no credentials needed
npm run test:live  # read-only tests against a real account (needs .env)
npm run test:all   # both
npm run dev        # watch mode
npm run smoke      # read-only self-test against the live API (needs .env)
npm run inspect    # MCP Inspector against the built server (needs .env)
```

### Tests

`npm test` runs offline and needs no easybill account — it covers response shaping,
the HTTP client against a mock API, the rate-limit throttle, and the MCP surface
(schemas, annotations, write-gating, error handling) driven over the real stdio protocol.

```
test/
├── helpers/mcp-client.mjs  minimal MCP stdio client + mock API server
├── format.test.mjs         field selection, pagination, truncation, markdown
├── client.test.mjs         auth headers, query serialisation, 429 retry, error mapping
├── rate-limit.test.mjs     sliding-window throttle
├── server.test.mjs         tool registration, workflow guidance, validation, errors
└── live.test.mjs           optional: read-only checks against a real account
```

`live.test.mjs` skips itself unless `EASYBILL_API_KEY` is set, so contributors without an
account still get a green suite. It only reads — nothing in the test suite writes to easybill.

Project layout:

```
src/
├── index.ts              entry point, stdio transport, env validation, --selftest
├── instructions.ts       MCP server instructions: workflow ordering for the agent
├── constants.ts          config, summary field sets, enums
├── schemas/common.ts     shared Zod building blocks
├── services/
│   ├── client.ts         HTTP, auth, throttling, retries, error mapping
│   └── format.ts         field selection, pagination, markdown, truncation
└── tools/
    ├── registry.ts       registration + write-gating
    ├── crud.ts           generic CRUD tool factory
    ├── search.ts         fuzzy customer lookup
    ├── documents.ts      documents + lifecycle actions
    ├── customers.ts      customers, contacts, groups
    ├── catalog.ts        positions, stock
    ├── finance.ts        payments
    ├── work.ts           projects, time tracking
    ├── files.ts          attachments, templates
    └── meta.ts           server info
```

Most resources are generated from a declarative config in `crud.ts`; only genuinely
resource-specific behaviour (document lifecycle, downloads, sending) is hand-written.

## Contributing

Issues and pull requests welcome. The tool surface is derived from easybill's official
OpenAPI spec (`https://api.easybill.de/rest/v1/swagger.json`) — when adding a tool, check
field names and types against the spec rather than guessing, and mind that monetary fields
are cents even where the spec types them as floats.

## Disclaimer

This is an **unofficial**, community-maintained project. It is not affiliated with,
endorsed by, or supported by easybill GmbH. "easybill" is a trademark of its respective
owner and is used here only to describe what this software talks to.

The software is provided as-is under the MIT license, without warranty. It can create,
modify and delete records in your accounting system, and can send invoices to your
customers. You are responsible for what you let it do — start read-only, and review what
write tools produce before relying on it.

## License

[MIT](LICENSE) © stack74