---
title: "Guardrails for AI agents, and app sign-in"
canonical: https://relayswitch.io/features/guardrails
generated: 2026-11-02T10:10:20.866Z
source: https://api.relayswitch.io/v1/catalog
base_url: https://api.relayswitch.io/v1
---

Guardrails and sign-in

# Rules an agent cannot talk its way past.

Block patterns, catch prompt injection in tool results and decide which tools a key may call, before any model sees the request. For apps, Sign in with RelaySwitch gives each user their own budgeted key.

[Get an agent key](https://app.relayswitch.io/console)[Code](#example)

Live

A blocked request

$0.00

Blocked patterns per policy

up to 50

Prompt-injection check

off, flag or block

Sign-in code lifetime

10 minutes

Claude Haiku 5.5, per M tokens

$0.06 in / $0.15 out

## What it does for an agent

Blocked patterns

Regular expressions checked against system, user and tool text. block stops the request; flag marks it.

Prompt-injection check

Override phrasings, role markers and hidden Unicode in tool output, caught locally with no model call.

Tool allow and deny lists

Function tools, server tools and MCP tools by name, with prefix wildcards. Denied tools never reach the model.

Per key or org-wide

An organization default plus each key’s own rules, combined stricter-wins.

Blocked costs nothing

A request stopped by a guardrail never reaches a model and is never billed.

Sign in with RelaySwitch

OAuth with PKCE: your app gets a key per user, funded by that user, capped at the limit they approved.

## Copy, paste, run

curl: organization default

bash

1`# The organization's default, layered under every key (admin key).`

2`curl -X PATCH https://api.relayswitch.io/v1/guardrails \`

3 `-H "Authorization: Bearer $ADMIN_KEY" -H "Content-Type: application/json" \`

4 `-d '{"guardrails": {`

5 `"blocked_patterns": [`

6 `{"pattern": "rm -rf /", "name": "rm-root"},`

7 `{"pattern": "(drop|truncate) table", "action": "flag", "name": "sql-ddl"}`

8 `],`

9 `"prompt_injection": "block",`

10 `"tool_policy": {"deny": ["web_fetch", "github__delete_*"]}`

11 `}}'`

Key API: one agent’s rules

bash

1`# A support agent that may only call two tools and flags injection attempts.`

2`curl https://api.relayswitch.io/v1/keys \`

3 `-H "Authorization: Bearer $ADMIN_KEY" -H "Content-Type: application/json" \`

4 `-d '{"name": "support-bot", "budget_usd": 20,`

5 `"guardrails": {"prompt_injection": "flag",`

6 `"tool_policy": {"allow": ["lookup_order", "web_search"]}}}'`

Anthropic SDK: handle a block

python

1`import anthropic`

2`import os`

3

4`client = anthropic.Anthropic(`

5 `base_url="https://api.relayswitch.io/v1",`

6 `api_key=os.environ["RELAYSWITCH_API_KEY"],`

7`)`

8

9`try:`

10 `reply = client.messages.create(`

11 `model="claude-haiku-5-5",`

12 `max_tokens=512,`

13 `messages=[{"role": "user", "content": scraped_page_text}],`

14 `)`

15`except anthropic.BadRequestError as err:`

16 `# 400 guardrail_blocked: no model was asked and nothing was charged`

17 `print(err.message)`

OpenAI SDK: read a flag

python

1`from openai import OpenAI`

2`import os`

3

4`client = OpenAI(`

5 `base_url="https://api.relayswitch.io/v1",`

6 `api_key=os.environ["RELAYSWITCH_API_KEY"],`

7`)`

8

9`raw = client.chat.completions.with_raw_response.create(`

10 `model="gpt-6.1-sol",`

11 `messages=[{"role": "user", "content": tool_output}],`

12`)`

13`if raw.headers.get("x-uplink-guardrail") == "flagged":`

14 `alert_on_call() # answered as usual, marked for review`

15`reply = raw.parse()`

## Sign in with RelaySwitch

Three steps in the browser: make a PKCE pair, send the user to https://app.relayswitch.io/auth, trade the code at POST /v1/auth/keys. No key needed for the exchange, any origin.

javascript

1`// 1. A verifier and its S256 challenge, in the browser.`

2`const b64url = (bytes) => btoa(String.fromCharCode(...bytes))`

3 `.replace(/\+/g, "-").replace(/\//g, "_").replace(/=+$/, "");`

4`const verifier = b64url(crypto.getRandomValues(new Uint8Array(32)));`

5`const digest = await crypto.subtle.digest("SHA-256", new TextEncoder().encode(verifier));`

6`const challenge = b64url(new Uint8Array(digest));`

7`sessionStorage.setItem("pkce_verifier", verifier);`

8

9`// 2. Send the user to approve a key with a $10 budget.`

10`location.href = "https://app.relayswitch.io/auth?" + new URLSearchParams({`

11 `callback_url: "https://yourapp.example/callback",`

12 `code_challenge: challenge,`

13 `code_challenge_method: "S256",`

14 `key_label: "YourApp",`

15 `limit: "10",`

16`});`

17

18`// 3. On the callback page, trade ?code= for the user's key.`

19`const code = new URLSearchParams(location.search).get("code");`

20`const res = await fetch("https://api.relayswitch.io/v1/auth/keys", {`

21 `method: "POST",`

22 `headers: { "content-type": "application/json" },`

23 `body: JSON.stringify({`

24 `code,`

25 `code_verifier: sessionStorage.getItem("pkce_verifier"),`

26 `code_challenge_method: "S256",`

27 `}),`

28`});`

29`const { key, key_id, limit_usd } = await res.json(); // key: sk-relay-live-...`

The callback must be https, or http on localhost, 127.0.0.1 or \[::1\]. The answer carries `key`, `key_id`, `name` and `limit_usd`; send the key as `Authorization: Bearer` on that user’s requests, and each one bills the user’s balance.

Agent setup guides

-   [OpenClaw](https://relayswitch.io/guides/openclaw)
-   [Hermes Agent](https://relayswitch.io/guides/hermes-agent)
-   [OpenCode](https://relayswitch.io/guides/opencode)
-   [Claude Code](https://relayswitch.io/guides/claude-code)
-   [n8n](https://relayswitch.io/guides/n8n)

More features

-   [Agent tools](https://relayswitch.io/features/agent-tools)
-   [Files and redaction](https://relayswitch.io/features/files)
-   [Routing](https://relayswitch.io/features/routing)
-   [Caching and compression](https://relayswitch.io/features/caching)
-   [MCP gateway](https://relayswitch.io/features/mcp-gateway)
-   [Endpoints](https://relayswitch.io/features/endpoints)
-   [Key budgets](https://relayswitch.io/features/key-budgets)
-   [Observability](https://relayswitch.io/features/observability)
-   [Hosted agents](https://relayswitch.io/agents)
-   [Workflows](https://relayswitch.io/workflows)
-   [Docs](https://relayswitch.io/docs)

FAQs

## Questions

For agent builders.

Open the console

A key in under a minute

[Get a key](https://app.relayswitch.io/console)

Or email [hello@relayswitch.io](mailto:hello@relayswitch.io)

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## Put limits on what your agents send

Guardrails on any key, and sign-in that hands each of your users a budgeted key.

[All features](https://relayswitch.io/features)[Get an agent key](https://app.relayswitch.io/console)