Overview
The Limits SDK (@limits/js) provides a type-safe interface to the Limits Policy API. Your application triggers evaluation via the SDK; the SDK sends requests to the Limits API and returns allow, block, or escalate decisions.
You can:
- Check conditions — evaluate policies with structured input (e.g. amount, currency).
- Evaluate instructions — validate prompt + LLM response (e.g. in middleware).
- Run guardrails — check text (e.g. safety, PII) before sending to the user.
- List, approve, and decline escalations.
Integrate with LangChain. You can use the SDK inside LangChain custom middleware to run guardrails, instructions, and conditions on your agent. See LangChain integration. PolicyEvaluationResult, Escalation, EscalationResponse) are exported from @limits/js. The SDK uses native fetch (Node.js 18+).
Requirements
| Requirement | Version |
|---|
| Node.js | >= 18.0.0 (for native fetch) |
| TypeScript | >= 5.0 (optional, for types) |
Installation
Install the Limits SDK using your preferred package manager:
Configuration
Constructor: new Limits(config)
Create a single client instance and reuse it for all calls.
| Parameter | Type | Required | Description |
|---|
config.apiKey | string | Yes | API key. Must start with sk_. |
InvalidAPIKeyError if the key is missing or doesn’t start with sk_.
import { Limits } from '@limits/js';
const limits = new Limits({
apiKey: process.env.LIMITS_API_KEY!,
});
Authentication
- Header:
Authorization: Bearer <apiKey>
- API keys must start with
sk_ and be valid in your Limits account.
Get Your API Key
Get an API key from the Limits dashboard: Dashboard → API keys. Add it to your environment variables.
export LIMITS_API_KEY="sk_your_api_key_here"
Never commit your API key to version control. Use environment variables or a secrets manager.
Quick Example
After creating the client, you typically call check, evaluate, or guard with a policy identifier and your input. The result tells you whether the action is allowed, blocked, or needs review (escalation).
import { Limits } from '@limits/js';
const limits = new Limits({
apiKey: process.env.LIMITS_API_KEY!,
});
const decision = await limits.check('amount-minimum-usd', { amount: 500, currency: 'USD' });
if (decision.isBlocked) console.error(decision.data.reason);
else if (decision.isEscalated) console.warn('Needs review:', decision.data.reason);
else console.log('Allowed');
Next Steps
