> ## Documentation Index > Fetch the complete documentation index at: https://www.truefoundry.com/llms.txt > Use this file to discover all available pages before exploring further. # Arthur AI > Arthur GenAI Engine stateless validation on TrueFoundry AI Gateway via a deployable FastAPI wrapper. Deploy the [`integrations/arthur-ai`](https://github.com/truefoundry/integrations-custom-guardrails/tree/main/integrations/arthur-ai) **FastAPI wrapper** on any **public HTTPS** host. The gateway calls it at `llm_input` / `llm_output` via the [Custom Guardrail](/docs/ai-gateway/custom-guardrails) contract; the wrapper forwards traffic to [Arthur GenAI Engine](https://platform.arthur.ai) and returns `verdict` JSON on HTTP 200. ## What is Arthur AI? [Arthur GenAI Engine](https://platform.arthur.ai) is a SaaS platform for validating LLM prompts and completions. The wrapper calls `POST /api/v2/validate` and maps rule results to pass/block — it does not embed policy logic beyond the checks you configure. Arthur is **validate-only**. Use **Operation: Validate** for both input and output rails. It reports failures but does not redact or rewrite text. Default checks when `config` is `{}`: * **Input:** `PromptInjectionRule` + `ToxicityRule` * **Output:** `ToxicityRule` ## How it works 1. The gateway POSTs an OpenAI-shaped `requestBody` (input) or `requestBody` + `responseBody` (output) to your wrapper URL. 2. The wrapper extracts user/assistant text and calls Arthur with your `ARTHUR_API_KEY`. 3. The wrapper returns **HTTP 200** with a policy outcome in the body. Infrastructure failures return **HTTP 5xx**. ``` TF customer's app ─► TF gateway ─► this wrapper ─► engine.platform.arthur.ai/api/v2/validate ``` ## Response contract | HTTP | Body | Meaning | | ----- | -------------------------------------- | ------------------------- | | `200` | `{"verdict": true}` | Allow | | `200` | `{"verdict": false, "message": "..."}` | Block (policy) | | `5xx` | error JSON | Wrapper or Arthur failure | Policy blocks use **2xx + `verdict: false`**, not HTTP 4xx. See [Custom guardrail response contract](/docs/ai-gateway/custom-guardrails#custom-guardrail-response-contract). ## Wrapper endpoints | Path | Target | | ------------------ | ----------------- | | `/validate-input` | Request (input) | | `/validate-output` | Response (output) | `GET /health` — health check. `GET /debug/loaded-config` — bearer-gated diagnostics. All POST routes expect `Authorization: Bearer `. ## Prerequisites * **Arthur API key** from the [Arthur platform](https://platform.arthur.ai). * **Public HTTPS URL** for the deployed wrapper. * **`WRAPPER_API_KEY`** — shared secret the gateway sends as `Authorization: Bearer …`. ## Setup ```bash theme={"dark"} git clone https://github.com/truefoundry/integrations-custom-guardrails cd integrations-custom-guardrails/integrations/arthur-ai cp .env.example .env ``` ```bash .env theme={"dark"} ARTHUR_API_KEY= WRAPPER_API_KEY= ``` **TrueFoundry:** ```bash theme={"dark"} pip install -U truefoundry tfy login python deploy.py --wait ``` Set `TFY_WORKSPACE_FQN`, `TFY_PUBLIC_HOST`, `TFY_PUBLIC_PATH`, and secret FQNs in `.env`. Create secrets `arthur-api-key` and `wrapper-api-key` under group `arthur-guardrails-tfy` in **Platform → Secrets**. **Local:** ```bash theme={"dark"} python3 -m venv .venv .venv/bin/pip install -r requirements-dev.txt .venv/bin/uvicorn main:app --reload --port 8000 ``` **AI Gateway → Guardrails → + Add New Guardrails Group** → type **Custom**. * **Group name**: `arthur-ai` * Add two configs — input and output. **Input validate** example: | Field | Value | | ---------------------- | --------------------------------------------------------------------------------- | | **Name** | `arthur-input-validate` | | **Operation** | Validate | | **Target** | Request | | **Enforcing Strategy** | Enforce But Ignore On Error | | **URL** | `https:///validate-input` | | **Headers** | `Authorization` → `Bearer `; `Content-Type` → `application/json` | | **Config** | `{}` | TrueFoundry custom guardrail form: Validate, Request target, /validate-input URL, Authorization Bearer header **Output validate:** | Field | Value | | ------------- | -------------------------------- | | **Name** | `arthur-output-validate` | | **Operation** | Validate | | **Target** | Response | | **URL** | `https:///validate-output` | **Auth Data → Custom Bearer Auth** works the same as **Headers** if you prefer not to set headers manually. **Model pin**: **AI Gateway → Models → \ → Guardrails** → attach group `arthur-ai`. **Per request** — `X-TFY-GUARDRAILS` header, selector format `/`: ```json theme={"dark"} { "llm_input_guardrails": ["arthur-ai/arthur-input-validate"], "llm_output_guardrails": ["arthur-ai/arthur-output-validate"] } ``` ## Custom config (optional) Override defaults by setting `config.checks` in the dashboard: ```json theme={"dark"} { "checks": [ {"name": "prompt-injection-check", "type": "PromptInjectionRule", "apply_to_prompt": true, "apply_to_response": false}, {"name": "toxicity-check", "type": "ToxicityRule", "apply_to_prompt": true, "apply_to_response": false, "config": {"threshold": 0.5}} ], "fail_closed_on_unavailable": false } ``` | Key | Purpose | | ------------------------------- | ---------------------------------------------------------------------- | | `credentials.apiKey` | Override `ARTHUR_API_KEY` env var | | `api_base` | Override Arthur API host (default `https://engine.platform.arthur.ai`) | | `timeout` | Request timeout in seconds (default 30) | | `context` / `grounding_context` | Grounding text for hallucination checks | | `fail_closed_on_unavailable` | Block when Arthur returns Skipped/Unavailable (default `false`) | ## Troubleshooting | Symptom | Likely cause | | ---------------------------------------------- | ------------------------------------------------------------------------------ | | `401` from wrapper | `WRAPPER_API_KEY` on the service does not match the dashboard Bearer token | | Gateway allows despite `verdict: false` | Tenant gateway not honoring verdict-on-200; set **Enforce** or upgrade gateway | | Arthur Skipped/Unavailable but traffic allowed | Default behavior; set `fail_closed_on_unavailable: true` in config | | Wrong checks running | Curl `/debug/loaded-config` with Bearer auth to inspect loaded config | ## Reference | Item | Value | | --------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Source repo | [`truefoundry/integrations-custom-guardrails/integrations/arthur-ai`](https://github.com/truefoundry/integrations-custom-guardrails/tree/main/integrations/arthur-ai) | | Arthur platform | [platform.arthur.ai](https://platform.arthur.ai) | | Arthur API | `POST https://engine.platform.arthur.ai/api/v2/validate` | | Selector | `arthur-ai/` |