QuickJS

The QuickJS guardrail lets you write custom validation logic in JavaScript. The script is executed locally within Otoroshi using the QuickJS engine (via WASM), providing a lightweight way to implement custom guardrails without compiling a full WASM plugin.

It can be applied before sending the prompt to the LLM and after to validate the LLM response.

How it works

1. The guardrail loads the JavaScript code from the configured path
2. It executes the guardrail_call function exported by the script, passing the messages and configuration as a JSON string argument
3. The function returns a result indicating whether the message should pass or be denied

Configuration

"guardrails": [
  {
    "enabled": true,
    "before": true,
    "after": true,
    "id": "quickjs",
    "config": {
      "jsPath": "https://my-server.example.com/guardrails/my-guardrail.js"
    }
  }
]

Field explanations

• enabled: true — The guardrail is active
• before: true — The guardrail applies to user input before sending to the LLM
• after: true — The guardrail applies to the LLM response

Config section

Parameter	Type	Required	Default	Description
jsPath	string	Yes	—	Path or URL to the JavaScript file containing the guardrail logic. Can also be specified as quickjs_path.

JavaScript function signature

The JavaScript file must export a guardrail_call function:

exports.guardrail_call = function(args) {
  const { messages, config, provider, attrs } = JSON.parse(args);

  // Your validation logic here

  return JSON.stringify({
    pass: true,
    reason: "none"
  });
};

Function input

The args parameter is a JSON string containing:

{
  "config": { /* guardrail config */ },
  "provider": { /* provider config or null */ },
  "attrs": { /* request attributes */ },
  "messages": [
    { "role": "user", "content": "the message" }
  ]
}

Expected output

The function must return a string. Accepted formats:

Output	Result
"pass" or "true"	Message passes
"deny" or "false"	Message is denied
{"pass": true}	Message passes
{"pass": false, "reason": "explanation"}	Message is denied with a custom reason
{"error": "message"}	Guardrail error

Example

exports.guardrail_call = function(args) {
  const { messages } = JSON.parse(args);

  for (const msg of messages) {
    const content = msg.content || '';
    if (content.toLowerCase().includes('password')) {
      return JSON.stringify({
        pass: false,
        reason: "Message contains sensitive keyword 'password'"
      });
    }
  }

  return JSON.stringify({
    pass: true,
    reason: "none"
  });
};