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Bill4Time MCP server

Give Claude and other MCP clients read-only access to Bill4Time billing, time and trust data.

Bill4Time MCP server is a Model Context Protocol server for Bill4Time, the time tracking and billing platform. It registers 59 tools, all read-only. It runs over stdio by default, for desktop clients such as Claude Desktop, and offers an opt-in stateless Streamable HTTP mode that implements MCP specification 2026-07-28. Bill4Time credentials stay on the machine that runs the server: they come from the setup command and your operating system's keyring, never from the client. The Bill4Time API is currently read-only.

Features

• Clients: list clients, filter by status, and look up active or disabled clients.
• Projects: list projects, and filter by client, status or billing method.
• Time entries: list by client, project, user, invoice, date range or billing status.
• Expenses: list by client, project, invoice or date range.
• Invoices: list by status (prebill, finalized, paid, partially paid, unpaid), client, project or date range.
• Payments: list payments by client, project or date range, and see which invoices each payment was applied to.
• Contacts and users: list contacts by status or date range, list contact connections, and look up users.
• Trust accounting: list trust records by client, project or date range.
• Filtering: pass OData-style filter_expr expressions to the general list tools for advanced queries.

Tools

The server registers 59 tools, all of them read-only.

<details> <summary>All 59 tools</summary>

• get_client
• get_contact
• get_expense
• get_invoice
• get_payment
• get_payment_applied
• get_project
• get_time_entry
• get_trust_record
• get_user
• list_active_clients
• list_active_contacts
• list_clients
• list_closed_projects
• list_contact_connections
• list_contact_connections_for_client
• list_contact_connections_for_contact
• list_contact_connections_for_project
• list_contacts
• list_contacts_for_date_range
• list_disabled_clients
• list_expenses
• list_expenses_for_client
• list_expenses_for_date_range
• list_expenses_for_invoice
• list_expenses_for_project
• list_finalized_invoices
• list_invoices
• list_invoices_for_client
• list_invoices_for_date_range
• list_invoices_for_project
• list_open_projects
• list_paid_invoices
• list_partially_paid_invoices
• list_payments
• list_payments_applied
• list_payments_applied_for_date_range
• list_payments_applied_for_invoice
• list_payments_applied_for_payment
• list_payments_for_client
• list_payments_for_date_range
• list_payments_for_project
• list_prebill_invoices
• list_projects
• list_projects_by_billing_method
• list_projects_for_client
• list_time_entries
• list_time_entries_by_billing_status
• list_time_entries_for_client
• list_time_entries_for_date_range
• list_time_entries_for_invoice
• list_time_entries_for_project
• list_time_entries_for_user
• list_trust_records
• list_trust_records_for_client
• list_trust_records_for_date_range
• list_trust_records_for_project
• list_unpaid_invoices
• list_users

</details>

Prompts and resources

The server also registers three prompts and three resources.

Requirements

• Python 3.10 or later.
• A Bill4Time account with an API key (create one in Settings → API tab).
• An MCP client such as Claude Desktop.

Installation

Install uv, then clone the repository and install its locked dependencies:

git clone https://github.com/RosenAdvertising/bill4time-mcp.git
cd bill4time-mcp
uv sync --locked

Releases are also published to PyPI: pip install bill4time-mcp installs version 0.3.0, which predates the HTTP mode described below. Install from source to use HTTP mode.

Configuration

Run the setup command once. It prompts for your API key, tests the connection, and saves the key to your operating system's keyring (see Credential storage):

uv run bill4time-mcp-setup

After changing the API key, restart the MCP server or client session so the new key is loaded.

Check the connection:

uv run bill4time-mcp-verify

Server messages that say to run bill4time-mcp-setup mean uv run bill4time-mcp-setup from your clone.

The server reads these variables, which you can also set in its environment:

Credential storage

By default the API key is stored in your operating system's native secret store via the cross-platform keyring library:

The secret is saved under the service name bill4time-mcp. Nothing is written to disk in clear text.

File fallback. On a host with no keyring backend (e.g. a headless Linux box without Secret Service), or if you set BILL4TIME_MCP_USE_KEYRING=0, the key falls back to a ~/.bill4time-mcp/.env file with 0600 permissions.

On Windows, the file is stored in the user's profile and protected by Windows' default per-user access rules. On POSIX, files are created with 0600 permissions and writes fail closed if private permissions cannot be established.

Read order. A key already set in the process environment wins. Otherwise the server reads the OS keyring, then the .env file fallback. To make a key rotated in the keyring take effect, unset BILL4TIME_API_KEY in the shell that starts the server.

Pluggable backend. keyring lets you point at any secret store. For example, install keyrings.cryptfile for an encrypted file backend, or a cloud backend, then select it with the standard PYTHON_KEYRING_BACKEND environment variable or a keyringrc.cfg. See the keyring configuration docs.

Usage with Claude Desktop

Add the server to Claude Desktop's configuration file (~/Library/Application Support/Claude/claude_desktop_config.json on macOS, %APPDATA%\Claude\claude_desktop_config.json on Windows):

{
  "mcpServers": {
    "bill4time": {
      "command": "uv",
      "args": ["run", "--locked", "--directory", "/absolute/path/to/bill4time-mcp", "bill4time-mcp"]
    }
  }
}

Replace /absolute/path/to/bill4time-mcp with the path of your clone, then restart Claude Desktop. Any other stdio MCP client uses the same command and arguments.

HTTP mode

Stdio is the default. Set BILL4TIME_MCP_TRANSPORT=streamable-http to serve the stateless Streamable HTTP transport from MCP specification 2026-07-28 at /mcp. Each request stands alone: no initialization handshake and no Mcp-Session-Id. Clients on earlier protocol versions are served on the same endpoint.

Security: this endpoint has no authentication and no TLS. Anyone who can reach the port can run every tool with this server's vendor credentials. Keep the default loopback bind (127.0.0.1), or put the server behind an authenticating TLS proxy on a private network. BILL4TIME_MCP_ALLOWED_HOSTS and BILL4TIME_MCP_ALLOWED_ORIGINS protect against browser DNS rebinding, not against direct callers. A proxy in front of it needs connection and idle timeouts: a legacy-style GET /mcp with Accept: text/event-stream holds a stream open until the client disconnects.

Bill4Time credentials come from the same configuration as stdio (see Configuration), never from the request.

BILL4TIME_MCP_TRANSPORT=streamable-http PORT=8080 uv run --locked bill4time-mcp

Point the MCP client at http://127.0.0.1:8080/mcp.

Error handling

A failed tool call returns an MCP error result (isError). Expected failures return a fixed message prefixed with Error executing tool and the tool name, for example "Error executing tool list_clients: Bill4Time resource was not found. Check the requested record." The server never passes a Bill4Time response body, a request URL or the API key back to the client.

Every Bill4Time request has a 30-second timeout. The server does not retry failed requests and does not follow redirects. A failed resource read returns the same fixed messages, "Bill4Time resource was not found." for an unknown resource and "Error reading resource" for an unexpected failure.

At startup the server exits with a message on stderr and a non-zero status when BILL4TIME_MCP_TRANSPORT is neither stdio nor streamable-http, when PORT is not an integer, or when a non-loopback BILL4TIME_MCP_HOST is set without BILL4TIME_MCP_ALLOWED_HOSTS.

Authentication notes

Bill4Time uses an API key embedded directly in the URL path:

https://secure.bill4time.com/b4t-api/{api_key}/v1/{resource}

No OAuth or token refresh required. Create API keys from Settings → API in your Bill4Time account.

OData filtering

General collection list tools accept a filter_expr parameter for advanced filtering:

"status eq 'Active'"
"clientId eq 751"
"invoiceDate ge '2024-01-01' AND invoiceDate le '2024-12-31'"
"billingStatus eq 'Ready For Billing'"

Supported operators: eq, ne, gt, ge, lt, le

Every list tool defaults to 50 records and an explicit deterministic sort (id desc, except the alphabetical open-project view). Use top to choose a total result cap from 1 through 200, orderby to override the sort, and skip for pagination on the general collection tools.

Example usage in Claude

"Show all unpaid invoices"

>

"List time entries for project 456 this month"

>

"Get all payments received from client 123 in 2024"

>

"Show trust account activity for client 789"

>

"List open projects ordered by project name"

Security note

API key in URL path. Bill4Time's API design embeds the API key directly as a path segment in every request URL (/b4t-api/{api_key}/v1/...). This is a Bill4Time API architecture constraint. The MCP resolves the key from the OS keyring, process environment, or a local file fallback; it never logs the key. However, the key-in-URL design has the following implications you should be aware of:

• Server/proxy access logs on any machine between your client and Bill4Time's servers will record the full request URL, including the API key, for the duration of their log retention policy.

• Network monitoring tools that capture request URLs (e.g. HTTP proxies, security appliances, debugging tools) will expose the key in logged URLs.

• If your key is compromised, all API access to your Bill4Time account — billing data, client records, invoices, payments — is accessible until the key is rotated.

Recommended practices:

1. Rotate your API key periodically (quarterly at minimum) from Settings → API in your Bill4Time account.

1. Keep access logs on this machine private — ensure ~/.bill4time-mcp/ is not world-readable, and that any HTTP proxy or network capture tool running on this machine is restricted to authorised users.

1. Rotate immediately if you suspect the key has been exposed (e.g. via a shared log file, a network trace, or an accidental curl -v paste).

1. Use least-privilege — if Bill4Time offers read-only API keys in the future, prefer those for this MCP (all current tools are read-only).

Testing

The test suite runs offline and needs no Bill4Time account: every Bill4Time API call is answered by an in-process stub session or by a stub HTTP server on 127.0.0.1. It covers list tool arguments and limits, error handling, credential file handling, the setup and verify commands, the stdio server, and the Streamable HTTP transport including the 2026-07-28 wire format, Host and Origin checks and stateless requests.

uv sync --locked
uv run --locked pytest -q

CI runs the suite on every push and pull request to main.

License

MIT. See LICENSE.