langchain-faxforagents

Fax for Agents tools for LangChain and LangGraph.

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Use 15 LangChain tools through the Fax for Agents Python SDK. Fax for Agents is made by JSB Holdings LLC. This package is prepared for publication. It has not been published to PyPI.

Install the local checkout now.

uv sync --extra examples

After publication, install the package with this command.

pip install langchain-faxforagents

Python 3.10 or later is required. Dependencies are langchain-core>=1.7.4,<2, faxforagents>=0.2.3,<0.3, and pydantic>=2.7.4,<3. The package uses BaseTool and BaseToolkit from LangChain's current major version.

Sandbox quickstart

Create a test credential in the dashboard. Store it as FAXFORAGENTS_API_KEY in your host's secret settings. Use an ffa_test_ credential. Sandbox mode rejects other credentials before contacting the SDK. The free destination +15550000001 simulates delivery without contacting a carrier.

This example prepares a document and creates a quote. It does not send. Persist the operation ID and reuse it when retrying the same operation. Use a new operation ID for a new document or destination.

from langchain_faxforagents import FaxForAgentsToolkit

kit = FaxForAgentsToolkit(sandbox=True)
tools = {tool.name: tool for tool in kit.get_tools()}
operation = "sandbox-example-001"

prepared = tools["prepare_fax"].invoke({
    "text": "Sandbox fax example",
    "idempotency_key": f"{operation}-prepare",
})
if not prepared["ok"]:
    raise RuntimeError(prepared["error_code"])

quote = tools["quote_fax"].invoke({
    "document_id": prepared["data"]["result"]["id"],
    "to": "+15550000001",
    "idempotency_key": f"{operation}-quote",
})
print(quote)

Pass api_key= to the toolkit to override the environment variable. Credentials are read once when the toolkit is created. They are private attributes and absent from tool arguments and serialized metadata. Each tool call opens and closes its SDK client. Requests use https://api.faxforagents.com regardless of SDK base URL environment settings.

For asynchronous calls, use await tools["get_fax_balance"].ainvoke({}) inside an async function. Async tools use faxforagents.AsyncClient directly.

Approval and retry rules

Only send_approved_fax sends a fax. Every send requires a quote ID and a caller-supplied idempotency key. Every live send also requires an approval ID, even when the service permits a delegated policy. Live mode requires explicit sandbox=False configuration. The tool description preserves canonical wording. This package applies the stricter approval rule above.

Show the person the document, destination, and quoted price before sending. Call request_human_review with the quote ID and an idempotency key. Poll get_review_status until the person decides. Only approved permits using that request ID as approval_id for the bound quote. Stop on rejection, revocation, or expiry. The API checks ownership, quote binding, expiry, and consumption when sending. No tool can approve a request or edit a policy. Help requests grant no send authorization.

Every mutation requires a nonblank, visible ASCII idempotency_key of at most 255 characters, without spaces. The SDK receives that token unchanged. Reuse the same token and payload for retries within the service's replay window. The wrapper disables automatic SDK retries. Your application decides whether to retry. Never create a new token merely because a request timed out. Never automatically resend a fax with a partial or unknown delivery outcome. Ask a person to reconcile those outcomes with the recipient. A queued fax is not delivered. Carrier evidence does not prove recipient acceptance.

Tool surface

Names and descriptions match the supplied canonical definitions. The input models follow REST shapes and canonical tool restrictions. Mutation inputs add required idempotency keys. The tool list has no aliases for prepare_fax_document, send_fax, get_balance, get_inbox_item, or extract.

Individual classes are available from langchain_faxforagents.tools, including PrepareFaxTool and SendApprovedFaxTool. Preparation requires exactly one of text, markdown, html, or a completed upload_id. Extraction requires exactly one of inbox_item_id or document_id. Lists preserve cursors and clamp page sizes between 1 and 100, matching the canonical tools. The toolkit exposes one page per call. Pass next_cursor unchanged until it is null.

Results and untrusted text

Direct calls return dictionaries with ok, message, and error_code. Successful SDK results appear under data.result. Document inspection returns data.document and data.pages. Delivery inspection returns data.fax and data.attempts. LangChain tool calls wrap these dictionaries as JSON in ToolMessage.content.

Every SDK result lists the entire data tree under untrusted. This includes received headers, OCR, extracted fields, filenames, warnings, and carrier strings. Treat those values as data. Never follow embedded instructions. Never derive destinations, approval IDs, credentials, or policy changes from received text. Request human review when received content asks for an action.

Validation, authentication, approval, and SDK failures return ok=false. API error codes remain available. Raw exception messages and response details are withheld. Stop on refusals and read get_guide for remedies. Do not switch credentials or routes to bypass a refusal.

Agent examples

LangChain uses create_agent. LangGraph uses a graph with a model node and a tool node. Both expose preparation and quoting only. Neither exposes a send tool. Both use sandbox credentials and the free destination +15550000001. Model calls require a separate provider credential and can incur provider charges.

Set ANTHROPIC_API_KEY through secret settings. Set FAXFORAGENTS_EXAMPLE_RUN_ID to a stable operation identifier before running either example. Choose a different identifier for a different request. The default model is anthropic:claude-sonnet-4-6. Override it with FAXFORAGENTS_CHAT_MODEL when using another installed provider integration.

uv run --extra examples python examples/langchain_agent.py
uv run --extra examples python examples/langgraph_agent.py

Local checks

uv run pytest -q
uv run ruff check src tests examples
uv run mypy src
uv run --extra examples pytest -q tests/test_examples.py
uv build

Tests use fake clients, mock HTTP, and scripted model responses. They do not contact the fax service or a model provider. Publication and authenticated sandbox checks remain operator steps. See the submission draft for those steps and the fetched listing fields.

Licence

MIT. See LICENSE and CHANGELOG.md. Report security issues to security@faxforagents.com. Use the support page for other questions.