SDK API

This is the canonical reference for the Python SDK. For tutorial-style introductions see Quickstart; for framework-specific patterns see the Framework adapters.

`proofrail.init()`

Configure the SDK. Call once at application startup before opening any chains.

proofrail.init(
    api_key: str,
    *,
    environment: str = "production",
    backend_url: str = "https://api.proofrail.dev",
    backend_timeout_seconds: float = 5.0,
    fail_modes: dict[str, str] | None = None,
    fail_mode: str | None = None,
    financial_approval_threshold_usd: float = 5000.0,
    cumulative_financial_threshold_usd: float = 10000.0,
    external_domains_allowlist: list[str] | None = None,
    high_risk_agents: list[str] | None = None,
    default_approval_timeout_hours: float = 24,
    fallback_approvers: list[str] | None = None,
    sensitive_field_patterns: list[str] | None = None,
    sensitive_value_patterns: list[str] | None = None,
    max_payload_string_length: int = 1000,
    enable_local_fast_path: bool = True,
    offline_buffer_max_events: int = 100,
)

Required

Parameter	Type	Description
`api_key`	`str`	Your ProofRail API key, prefixed `prail_`. Treated as a secret.

Common

Parameter	Type	Default	Description
`environment`	`str`	`"production"`	Tag attached to every chain. Common values: `"production"`, `"staging"`, `"development"`.
`backend_url`	`str`	`"https://api.proofrail.dev"`	Override for self-hosted or testing deployments.
`backend_timeout_seconds`	`float`	`5.0`	Per-request timeout when calling the backend. Should be raised for high-latency networks (e.g., 15s for Supabase free-tier).

Failure handling

Parameter	Type	Default	Description
`fail_modes`	`dict[str, str]`	See Configuration	Per-action-class behavior when the backend is unreachable. Keys are action categories (`financial`, `external_communication`, etc.); values are `"deny"` or `"allow"`. A `default` key sets the fallback for unmatched categories.
`fail_mode`	`str`	None	Legacy single-string parameter. Treated as `{"default": fail_mode}`. Don’t pass both `fail_modes` and `fail_mode`.
`offline_buffer_max_events`	`int`	`100`	Number of events buffered locally if the backend is unreachable. Oldest events drop when the buffer fills.

Policy thresholds

Parameter	Type	Default	Description
`financial_approval_threshold_usd`	`float`	`5000.0`	Single transactions above this require approval.
`cumulative_financial_threshold_usd`	`float`	`10000.0`	Chain cumulative financial exposure above this requires approval on the next financial action.
`external_domains_allowlist`	`list[str]`	None	Domains agents may communicate with without triggering exfiltration alerts.
`high_risk_agents`	`list[str]`	None	Agent names treated as high-risk; every action by these agents requires approval.
`default_approval_timeout_hours`	`float`	`24`	How long approval requests stay valid before timing out.
`fallback_approvers`	`list[str]`	None	Email addresses that receive escalations if primary approvers don’t respond within half the timeout.

Privacy

Parameter	Type	Default	Description
`sensitive_field_patterns`	`list[str]`	See Sanitization defaults	Field-name substrings that get redacted in payloads sent to the backend. Match is case-insensitive substring against keys.
`sensitive_value_patterns`	`list[str]`	See Sanitization defaults	Value prefixes that get redacted. Match uses `str.startswith()` against string values.
`max_payload_string_length`	`int`	`1000`	Strings longer than this are truncated before being sent.

Performance

Parameter	Type	Default	Description
`enable_local_fast_path`	`bool`	`True`	Allow obviously-safe actions to be decided locally without a backend round-trip. Disable for strictest governance (every action goes to the backend).

Returns

A ChainConfig instance. Configuration is also stored globally for the process so subsequent proofrail.Chain(...) calls use it.

Sanitization defaults

The SDK uses two separate default lists for redacting sensitive data: sensitive_field_patterns (default — matches against dict keys by case-insensitive substring):

["api_key", "password", "secret", "token", "credit_card", "ssn", "private_key"]

sensitive_value_patterns (default — matches against string values using str.startswith()):

["sk_", "pk_", "ghp_", "hf_", "eyJ", "AKIA", "prail_"]

Custom patterns you pass via the corresponding kwarg are appended to the defaults.

`proofrail.Chain`

Context manager that opens a chain and records every action within it. Use as an async or sync context manager depending on your code.

class Chain:
    def __init__(
        self,
        name: str,
        *,
        external_chain_id: str | None = None,
        metadata: dict | None = None,
    ): ...

    async def __aenter__(self) -> "Chain": ...
    async def __aexit__(self, exc_type, exc_val, exc_tb) -> None: ...

    def __enter__(self) -> "Chain": ...
    def __exit__(self, exc_type, exc_val, exc_tb) -> None: ...

    async def record_agent_action(...) -> PolicyDecision: ...
    def record_agent_action_sync(...) -> PolicyDecision: ...

Constructor parameters

Parameter	Type	Description
`name`	`str`	Human-readable identifier shown in the dashboard. Conventional: hyphen-separated lowercase (`"vendor-purchase"`, `"customer-onboarding"`).
`external_chain_id`	`str`	Your own ID for the chain, useful for cross-referencing with your internal systems. Stored unchanged.
`metadata`	`dict`	Arbitrary JSON-serializable key/value pairs. Attached to the chain and visible in receipts. Stored as opaque data — the SDK does not interpret keys within it.

Lifecycle

On __aenter__ / __enter__: a chain record is created on the backend; the chain ID is available as chain.id after entry. On __aexit__ / __exit__: the SDK calls POST /v1/chains/{chain_id}/complete, which seals the chain and triggers receipt generation on the backend. If exit was triggered by an exception, the chain is marked accordingly and the receipt reflects the failure mode.

Methods

`record_agent_action()` (async)

async def record_agent_action(
    self,
    agent_name: str,
    action_type: str,
    action_name: str,
    payload: dict,
    *,
    parent_agent_name: str | None = None,
    metadata: dict | None = None,
) -> PolicyDecision

Record an action and receive a policy decision.

Parameter	Type	Description
`agent_name`	`str`	Identifier for the agent taking the action.
`action_type`	`str`	Category of action. Common values: `tool_call`, `llm_call`, `state_update`.
`action_name`	`str`	Specific name within the type. For `tool_call`, the tool name (e.g., `search_web`, `send_email`).
`payload`	`dict`	The action’s inputs. Sanitized before sending.
`parent_agent_name`	`str`	Agent that delegated to this one, if any. Used for tracking hierarchical workflows.
`metadata`	`dict`	Action-level metadata. For LLM calls, include `model`, `input_tokens`, `output_tokens` for cost tracking.

Returns a PolicyDecision object on allow or allow_with_flag outcomes. Blocks until resolution on require_approval. Raises on deny.

`record_agent_action_sync()`

Synchronous form for non-async code. Same signature and behavior, but raises RuntimeError if called from inside a running event loop.

`chain.id`

The backend-assigned chain UUID. Available after __aenter__ / __enter__. Useful for logging or cross-system references:

async with proofrail.Chain("workflow") as chain:
    logger.info("Started chain", extra={"chain_id": chain.id})

`proofrail.PolicyDecision`

Returned by record_agent_action when the action is allowed (including after a human approval resolves).

@dataclass
class PolicyDecision:
    policy_decision: str                          # "allow" | "allow_with_flag"
    decision_reason: str = ""
    decision_source: str = "backend_evaluation"
    policy_name: str | None = None
    kill_switch_active: bool = False
    pause_reason: str | None = None
    remediation: str | None = None
    docs_url: str | None = None
    evaluation_mode: str | None = None
    shadow_decision: str | None = None
    estimated_cost_usd: float | None = None
    auto_paused: bool = False

Attribute	Type	Description
`policy_decision`	`str`	The outcome — `"allow"` or `"allow_with_flag"`. (Denials raise instead.)
`decision_reason`	`str`	Human-readable explanation if a policy matched. Empty string when no reason applies.
`decision_source`	`str`	Where the decision came from: `"backend_evaluation"`, `"local_fast_path"`, `"human_approval"`, or `"offline_stub"`.
`policy_name`	`str`	Name of the matched policy, if any.
`kill_switch_active`	`bool`	True if the org’s kill switch was found active during evaluation (in which case denials raise `ProofRailKillSwitchError`).
`pause_reason`	`str`	If the org was paused, the reason supplied at activation.
`remediation`	`str`	Suggested fix when a policy matched.
`docs_url`	`str`	Link to docs for this kind of decision.
`evaluation_mode`	`str`	`"enforce"` or `"shadow"` for the matching policy.
`shadow_decision`	`str`	When `evaluation_mode` is `"shadow"`, the decision the policy would have made in enforce mode.
`estimated_cost_usd`	`float`	For LLM call events, the computed cost.
`auto_paused`	`bool`	True if the chain auto-paused at this action (event-count, duration, or token-budget limit).

Framework adapters

Each adapter exposes a govern() function that wraps an existing framework object. See the framework-specific pages for usage details.

`proofrail.langgraph.govern()`

def govern(
    compiled_graph,
    chain_name: str = "langgraph_workflow",
    metadata: dict | None = None,
) -> GovernedGraph

See LangGraph adapter.

`proofrail.langchain.govern()`

def govern(
    agent_executor_or_chain,
    chain_name: str = "langchain_workflow",
    metadata: dict | None = None,
) -> GovernedChain

The agent_name for recorded events is derived from type(executor).__name__ at wrap time — it isn’t a govern() parameter. See LangChain adapter.

`proofrail.crewai.govern()`

def govern(
    crew,
    chain_name: str = "crewai_workflow",
    metadata: dict | None = None,
) -> GovernedCrew

See CrewAI adapter.

`proofrail.mcp.ProofRailMcpAdapter`

class ProofRailMcpAdapter:
    def __init__(
        self,
        *,
        chain: proofrail.Chain,
        agent_name: str,
        parent_agent_name: str | None = None,
    ): ...

    def install(self, server) -> None: ...
    async def handle_tool_call(self, tool_name: str, arguments: dict, handler) -> Any: ...
    def tool(self, tool_name: str | None = None): ...  # decorator

See MCP adapter.

`proofrail.client.verify_receipt()`

Verify a receipt’s signature and return its contents.

async def verify_receipt(receipt_id: str) -> ReceiptVerifyResponse

class ReceiptVerifyResponse(BaseModel):
    valid: bool
    receipt_number: str
    chain_id: str
    generated_at: str

The valid field indicates whether the receipt’s HMAC signature checks out. If invalid, the receipt has been tampered with or modified after signing. This is a thin client over the public verification endpoint at GET /v1/receipts/{receipt_id}/verify. The endpoint requires no authentication — anyone with a receipt ID can verify. See Audit receipts for the signing and hash-chaining model.

Exceptions

All exceptions live in proofrail.exceptions. The base for policy-driven errors is ProofRailPolicyError.

ProofRailPolicyError                # base for policy denials
├── ActionDeniedError               # Policy or human reviewer denied
├── PolicyViolationError            # Policy condition violated outside main eval path
└── ProofRailKillSwitchError        # Org kill switch is active

Exception
├── BackendUnavailableError         # Backend unreachable, fail_mode=deny
├── ChainTimeoutError               # Chain exceeded configured timeout
└── ChainAutoPausedError            # Auto-pause rule fired (events, duration, tokens)

See Exceptions reference for attributes and handling patterns.

Version compatibility

The SDK requires Python 3.10 or later (enforced at install time by pip). Supported framework version ranges are pinned in sdk/pyproject.toml; install ProofRail with a compatible version of your framework already installed. See Limitations for the current compatibility matrix.

Where to go next

Configuration

Detailed walkthrough of every init() option.

Exceptions

All exception types and how to handle them.

Framework adapters

Per-framework usage and edge cases.

Limitations

What ProofRail does and doesn’t do at current version.

​SDK API

​proofrail.init()

​Returns

​Sanitization defaults

​proofrail.Chain

​Constructor parameters

​Lifecycle

​Methods

​record_agent_action() (async)

​record_agent_action_sync()

​chain.id

​proofrail.PolicyDecision

​Framework adapters

​proofrail.langgraph.govern()

​proofrail.langchain.govern()

​proofrail.crewai.govern()

​proofrail.mcp.ProofRailMcpAdapter

​proofrail.client.verify_receipt()

​Exceptions

​Version compatibility

​Where to go next

Configuration

Exceptions

Framework adapters

Limitations

SDK API

`proofrail.init()`

Returns

Sanitization defaults

`proofrail.Chain`

Constructor parameters

Lifecycle

Methods

`record_agent_action()` (async)

`record_agent_action_sync()`

`chain.id`

`proofrail.PolicyDecision`

Framework adapters

`proofrail.langgraph.govern()`

`proofrail.langchain.govern()`

`proofrail.crewai.govern()`

`proofrail.mcp.ProofRailMcpAdapter`

`proofrail.client.verify_receipt()`

Exceptions

Version compatibility

Where to go next