@rentaltide/underwriter

Build a RentalTide coverage underwriter. You write underwriting; the SDK does signature verification, routing, validation and idempotent binds.

npm i @rentaltide/underwriter

import crypto from 'node:crypto';
import { createUnderwriter, decline, NO_QUOTE } from '@rentaltide/underwriter';

const rentaltide = createUnderwriter({ secret: process.env.SIGNING_SECRET });

rentaltide
  .quote(({ bookingSubtotal, days, currency }) => {
    if (bookingSubtotal < 50) return NO_QUOTE; // no card renders, booking proceeds
    return {
      quoteId: crypto.randomUUID(),
      premium: Math.max(bookingSubtotal * 0.065, 12),
      currency,
      coverageLimit: 25_000,
      depositEffect: 'reduce_to',
      depositEffectValue: 500,
      questionSchemaVersion: '2026-09-01',
    };
  })

  .schema(() => ({
    version: '2026-09-01',
    fields: [
      {
        id: 'date_of_birth',
        label: 'Date of birth',
        type: 'date',
        required: true,
        minAgeYears: 18,
      },
      { id: 'prior_claims_3y', label: 'Claims in the last 3 years?', type: 'checkbox' },
    ],
  }))

  .requote(({ basePremium, answers }) => {
    if (tooYoung(answers.date_of_birth)) return decline('Operator must be 18 or over.');
    return {
      decision: 'accepted',
      premium: answers.prior_claims_3y ? basePremium * 1.4 : basePremium,
    };
  })

  .bind(({ quoteId, bookingReference, renter }) => issuePolicy(quoteId, bookingReference, renter))
  .reschedule(({ policyId, startsAt, endsAt }) => ({ decision: 'accepted' }))
  .cancel(({ policyId }) => voidPolicy(policyId));

rentaltide.listen(8787);

What it handles so you don't

The signature. Timing-safe comparison, a five-minute timestamp window, and the HMAC taken over the raw bytes — JSON.stringify of a parsed body does not round-trip byte for byte, which is the quiet way a hand-rolled check ends up rejecting valid requests or accepting invalid ones.

Idempotent binds. RentalTide retries /bind on a timeout or a 5xx. The SDK remembers the policy against its quoteId and returns the same one, so a retry cannot write a second policy on the same booking — the most expensive mistake in this integration. Memory by default; pass store for production:

createUnderwriter({
  secret,
  store: {
    get: (quoteId) => db.policies.findByQuoteId(quoteId),
    set: (quoteId, policy) => db.policies.insert({ quoteId, ...policy }),
  },
});

The rules that fail quietly. A premium returned as "44.50", a reduce_to with no depositEffectValue (which renders to a renter as a saving and then changes nothing at hold time), a documentUrl over plain http, more than twelve questions, a regex with a nested quantifier. Each throws where the handler returned, with the reason, instead of becoming a card that silently never renders.

Anywhere you run

http.createServer(rentaltide.handler()); // Node
export default { fetch: rentaltide.fetch }; // Workers, Hono, Next route handlers
rentaltide.listen(8787); // or just this

Testing it

npm i -g @rentaltide/cli
rentaltide coverage test --url http://localhost:8787

Fifteen checks, signed exactly as the platform signs them, exit code included.

Contract

https://docs.rentaltide.com/developers/embedded-insurance/

Types for every payload ship with the package.