MainBook Bank Statement Converter

**A finance MCP server scoped to one job: turning PDF bank statements into checked JSON, Excel or

CSV — not a general accounting MCP.** It runs locally after one `mainbook-mcp auth login`, or over

MainBook's hosted endpoint at `https://mcp.mainbook.ai/mcp`, where your client signs you in with your

MainBook account. Existing `mb_live_` API keys keep working for scripts and older clients.

Point your assistant at a statement and ask for a spreadsheet. The PDF goes to

MainBook, which extracts every transaction, normalises dates to

`YYYY-MM-DD`, keeps money as exact amounts, and re-adds the statement so that

`opening balance + credits − debits` has to match the closing balance. Rows that do not fit are

flagged instead of being passed on quietly.

> Convert ~/Downloads/march-statement.pdf and save the Excel next to it.

  mainbook - convert_bank_statement (MCP)
  63 transactions · 4 pages · 4 credits
  Totals reconciled against the statement
  Saved to ~/Downloads/march-statement.xlsx

Done — 63 transactions. Opening 4,127.50 and closing 3,881.05 both match
the statement, and nothing was flagged.

What it is not

It does not connect to bank accounts and is not an Open Banking or bank-data API. It reads

statement files you already have. Nothing is scraped and no banking credentials are involved.

What you need

A MainBook account and the folders holding your statements. Conversion is the only tool that spends

page credits. Of the other four, `get_balance` and `list_conversions` only read, `get_conversion`

may write a result file, and `output_folder` changes a local preference; none of them changes

anything in your MainBook account.

Add it to your client

Sign in once from a terminal:

uvx mainbook-mcp auth login

The command opens MainBook in your browser, shows the same short code in both places, and waits for

your approval. It stores the credential in the OS keyring when the optional `keyring` package is

installed and working. Otherwise it uses `~/.config/mainbook/credentials.json` with private

directory and file permissions. Use `mainbook-mcp auth status` to check the active credential

server-side without spending page credits. `mainbook-mcp auth logout` revokes that stored key first,

then removes the local copy; if MainBook cannot be reached, it says plainly that the key may still be

active. Signing in again revokes the previously stored key before saving its replacement. The device

token response does not include an email or account ID, so status says that account identity was not

provided instead of guessing.

Then add one entry to your client's MCP configuration. This is the same block for Claude Desktop

(Settings → Developer → Edit Config), Claude Code, and Cursor; no key is copied into it:

{
  "mcpServers": {
    "mainbook": {
      "command": "uvx",
      "args": ["mainbook-mcp", "~/Downloads", "~/Desktop", "~/Documents"]
    }
  }
}

Codex reads TOML, so put the same thing in `~/.codex/config.toml`:

[mcp_servers.mainbook]
command = "uvx"
args = ["mainbook-mcp", "~/Downloads", "~/Desktop", "~/Documents"]

`uvx` comes with uv; install it once with `brew install uv` or

`curl -LsSf https://astral.sh/uv/install.sh | sh`. It fetches and runs the published package, so

there is nothing to download by hand and nothing to update. If you would rather not add uv, run

`pip install mainbook-mcp` and use `"command": "mainbook-mcp"` with the same arguments — you then

upgrade it yourself with `pip install -U mainbook-mcp`.

The folder arguments are the only places the server may read a statement from or write a result to;

anything outside them is refused. `MAINBOOK_ALLOWED_DIRS` sets the same list through the

environment instead, separated by the platform's `os.pathsep` (`:` on macOS/Linux, `;` on Windows).

Manual API key for scripts and CI

`MAINBOOK_API_KEY` takes precedence over any stored login. Keep the manual method for automation

where an interactive browser is not available. `auth login` warns when this variable will keep

overriding the newly stored credential:

export MAINBOOK_API_KEY="mb_live_REPLACE_ME"
mainbook-mcp

Create and revoke manual keys at . Never commit them.

Claude Desktop, without touching a config file

Claude Desktop also accepts a one-file bundle: Extensions → Install Extension… and pick

`mainbook.mcpb`. It asks for the API key and the folders in a dialog and manages its own Python

runtime, so nothing needs installing first. The config block above does the same job and is the

better fit if you already keep other servers there. Build the bundle from this directory with:

npx --yes @anthropic-ai/mcpb@2.1.2 validate manifest.json
npx --yes @anthropic-ai/mcpb@2.1.2 pack . dist/mainbook.mcpb

What it exposes

• `convert_bank_statement`: creates a paid page-credit job, uploads one PDF, starts conversion,

polls for up to 30-900 seconds, and returns the reviewed result. JSON stays inline. In local

stdio mode, XLSX/CSV bytes are written to disk and only the full path enters model context.

• `get_conversion`: checks a job after a timeout and returns JSON inline or writes XLSX/CSV to a

chosen local destination.

• `list_conversions`: returns one cursor page of account jobs plus `next_cursor`.
• `get_balance`: returns total, reserved, and available credits, all measured in PDF pages.
• `output_folder`: reads or changes the default local result folder.

Local stdio mode lists all five tools. Hosted HTTP mode lists exactly the first four;

`output_folder` is not advertised remotely because the server's disk does not belong to the client.

There are no tools for buying credits, payments, deleting jobs, or changing account data.

Tools that can create a conversion, write a local result file, or change the output preference are

marked non-read-only. `get_conversion` is read-only over hosted HTTP, where it writes no file, and

non-read-only over local stdio, where it may write XLSX or CSV. None is marked destructive because

existing result files are never replaced.

Where result files go

For local stdio clients (Claude Desktop, Claude Code, Cursor, and Codex), XLSX and CSV results are

written to the first available destination in this order:

1. `output_path` supplied to `convert_bank_statement` or `get_conversion` (an absolute filename or

an existing folder);

2. the folder remembered by `output_folder`;

3. next to the source PDF, with the same base name and the result extension.

`get_conversion` cannot infer the original PDF folder. Without `output_path` or a valid remembered

folder it returns a clear error instead of guessing a destination. Every successful file response

contains the absolute path and explains which rule selected it. Existing files are never replaced:

`statement.xlsx` is followed by `statement (2).xlsx`, then `(3)`, and so on.

Ask the client to call `output_folder` with no argument to see the current setting and every allowed

folder. Set it with an allowed absolute directory, or pass `next_to_source` to restore the default.

The preference is shared by local clients on the same machine in `~/.mainbook/preferences.json`.

A saved folder that is missing or no longer allowed is ignored, and that fallback is stated in the

result.

JSON remains inline. It is also written to a `.json` file only when an explicit `output_path` is

provided. In remote HTTP mode, local paths and `output_folder` are unavailable, because the server disk

does not belong to the client. XLSX/CSV comes back as a one-time download link that expires in

ten minutes when you signed in through OAuth, and as a REST download instruction when you

authenticated with a legacy `mb_live_` key.

Manual requirements and installation

• Python 3.11 or newer
• A MainBook account

From this directory:

python3 -m venv .venv
.venv/bin/python -m pip install .

To prefer the OS keyring over the private JSON fallback, install the optional extra in every

environment that runs the login command or the local server:

.venv/bin/python -m pip install '.[keyring]'

Use a plain install, not `pip install -e .`. In this checkout the editable install writes a `.pth`

file that the interpreter does not pick up, so `python -m mainbook_mcp` fails with "No module named

mainbook_mcp" while the package looks installed. An identical file under another name is honoured,

so the content is fine and the cause is still unexplained — a plain install sidesteps it entirely.

If you use the manual method for automation, keep `mb_live_...` values in a secret environment or

client configuration. Never commit them.

Streamable HTTP mode

MainBook runs this server for you at `https://mcp.mainbook.ai/mcp`, so a client that speaks remote

MCP needs nothing installed. Paste that URL into claude.ai, Claude Desktop, ChatGPT or Cursor and

sign in with your MainBook account when the client asks; no key is copied into the configuration.

Cursor takes a fixed client id instead of registering itself, so give it this block:

{
  "mcpServers": {
    "mainbook": {
      "url": "https://mcp.mainbook.ai/mcp",
      "auth": {
        "CLIENT_ID": "mainbook-cursor",
        "scopes": ["mainbook:read", "mainbook:convert"]
      }
    }
  }
}

A client that cannot sign in can still send a legacy key from

mainbook.ai/developer:

Authorization: Bearer mb_live_REPLACE_ME

Either credential is read from each request, so every user of a client reaches their own MainBook

account and spends their own page credits. `initialize` and `tools/list` answer without a

credential; every tool call requires one. Local file paths and `output_folder` do not exist over HTTP — pass `file_url` instead

of `file_path`, because the server's disk is not yours. XLSX or CSV results come back as a

one-time download link (ten minutes, single use) for OAuth sessions, or as a REST download

instruction for a legacy `mb_live_` key.

You can also run the same remote mode yourself. It is stateless Streamable HTTP with JSON responses:

mainbook-mcp --transport http --host 127.0.0.1 --port 8000

The MCP endpoint is then `http://127.0.0.1:8000/mcp`. Each client should send its own header:

Authorization: Bearer mb_live_REPLACE_ME

The header is read from each tool-call request and never stored in global state. Hosted HTTP mode

does not inspect `MAINBOOK_API_KEY`, the OS keyring, or the local credential file. For Codex remote

mode:

[mcp_servers.mainbook]
url = "https://mcp.mainbook.ai/mcp"
bearer_token_env_var = "MAINBOOK_API_KEY"
tool_timeout_sec = 920
default_tools_approval_mode = "writes"

Replace the URL with your own host if you deploy this yourself; a self-hosted deployment still needs

normal HTTPS termination and access controls.

OAuth on the hosted service

Account sign-in is live on `https://mcp.mainbook.ai/mcp` (since 2026-08-20). The verifier stays

disabled by default in this source tree, so a deployment you run yourself has to enable it

deliberately. Wherever it is enabled, `initialize` and `tools/list` remain public, while each tool

call accepts either an existing `mb_live_` key or a MainBook RS256 access token. OAuth tokens are verified locally against only the

configured MainBook JWKS URL; they are never forwarded to the Developer API. The MCP server sends a

fresh 60-second `X-MainBook-Service` credential for every internal REST request instead.

The hosted tool scopes are fixed in one map: `convert_bank_statement` requires

`mainbook:convert`; `get_balance`, `get_conversion`, and `list_conversions` require

`mainbook:read`. Protected-resource metadata is published at

`/.well-known/oauth-protected-resource/mcp` only while the flag is enabled.

Environment variables

• `MAINBOOK_API_KEY`: optional in stdio and takes precedence over a stored login; ignored in HTTP

mode, where every tool call must carry its own Bearer header.

• `MAINBOOK_API_BASE_URL`: REST host, default `https://api.mainbook.ai`. The server appends

`/api/v1/developer`.

• `MAINBOOK_ALLOWED_DIRS`: local folders allowed for source reads and result writes, separated by the platform's

`os.pathsep` (`:` on macOS/Linux and `;` on Windows). Positional directory arguments take

priority. If neither is supplied, the defaults are `~/Downloads`, `~/Desktop`, and

`~/Documents`.

• `MAINBOOK_MCP_TRANSPORT`: `stdio` (default) or `http`.
• `MAINBOOK_MCP_HOST`: HTTP bind host, default `127.0.0.1`.
• `MAINBOOK_MCP_PORT`: HTTP bind port, default `8000`.
• `MAINBOOK_MCP_OAUTH_ENABLED`: hosted OAuth verifier feature flag, default `false`. With the flag

off, metadata is absent and hosted Bearer handling remains the legacy `mb_live_` behavior.

• `MAINBOOK_MCP_OAUTH_ISSUER`: exact trusted issuer, default `https://api.mainbook.ai`.
• `MAINBOOK_MCP_OAUTH_JWKS_URL`: trusted JWKS URL, default

`https://api.mainbook.ai/.well-known/jwks.json`. Token header URLs are ignored.

• `MAINBOOK_MCP_OAUTH_RESOURCE`: exact audience/resource, default

`https://mcp.mainbook.ai/mcp`.

• `MAINBOOK_MCP_OAUTH_CLOCK_SKEW_SECONDS`: NumericDate clock allowance, default `5`.
• `MAINBOOK_MCP_OAUTH_MAX_TOKEN_AGE_SECONDS`: maximum accepted age from `iat`, default `600`.
• `MAINBOOK_MCP_OAUTH_JWKS_CACHE_TTL_SECONDS`: JWKS cache lifetime, default `300`.
• `MAINBOOK_MCP_OAUTH_JWKS_REFRESH_MIN_INTERVAL_SECONDS`: minimum interval between unknown-`kid`

refresh attempts, default `30`.

• `MCP_SERVICE_SIGNING_SECRETS`: comma-separated service-door secrets. MCP signs with the first;

Django may accept current and previous values during rotation. Required when OAuth is enabled;

never commit it.

File and network safety

• `file_path` and `file_url` are mutually exclusive. `file_path` is accepted only over local

stdio; HTTP mode rejects it before the filesystem loader runs and requires `file_url`.

• Local `file_path` access and result-file writes use the same configured folders. Positional CLI directories take

priority over `MAINBOOK_ALLOWED_DIRS`; the environment takes priority over the defaults

`~/Downloads`, `~/Desktop`, and `~/Documents`. Every root is expanded and resolved, missing

roots are ignored, and the active roots are printed to stderr when the server starts. If no

roots remain, local access fails closed while the server continues running.

• Output parents are resolved before writing and checked by directory identity, so a symlink cannot

redirect a result outside the allowed folders. Result creation is exclusive and collision-safe;

existing files are not overwritten.

• `~/.mainbook/preferences.json` is replaced atomically. The `.mainbook` directory is mode `0700`

and the preference file is mode `0600`; malformed or unreadable preferences are ignored safely.

• Terminal credentials use the OS keyring when the optional package is usable. The fallback

`~/.config/mainbook/credentials.json` is replaced atomically inside a mode `0700` directory and

is mode `0600`; its top-level entries are keyed by API base URL.

• Local paths are expanded and strictly resolved before the allowlist check, so `..` and symlinks

cannot make an outside target appear to be inside an allowed folder. The resolved path must be

strictly below a root, not equal to the root itself.

• The local file is opened once. The server uses `fstat` on that descriptor to require a regular

file and enforce the 50 MiB limit, then performs the bounded read through the same descriptor.

This closes the check-versus-read replacement window, but it does not fully eliminate the race

between resolving the path and opening it; the path can still be replaced during that interval.

• A local file must contain `%PDF-` within its first 1024 bytes before `pypdf` is invoked. Filename

extensions are not used to decide whether a file is a PDF.

• Remote files must use HTTPS. Redirects are not followed.
• DNS answers are rejected if any address is private, loopback, link-local, metadata, reserved, or

otherwise non-public, for IPv4 and IPv6.

• URL downloads connect to an already validated numeric IP while retaining the original hostname

for TLS certificate verification and the HTTP `Host` header, closing DNS-rebinding races.

• `Content-Length` and the actual streamed byte count are independently capped at 50 MiB.
• PDFs are parsed locally with `pypdf` and capped at 500 pages.
• Presigned upload headers from MainBook are forwarded unchanged; the MainBook Bearer key is never

sent to storage.

Development checks

.venv/bin/python -m pip install '.[dev]'
.venv/bin/pytest
.venv/bin/pytest --cov=mainbook_mcp --cov-report=term-missing --cov-report=annotate:cov_annotate
.venv/bin/ruff check .

All REST tests use mocks or a local stub. No test requires or accepts a real MainBook API key.