1. Validate the input against a Zod schema built from the form's registered fields. The schema trims values, checks required fields and length limits, and strips unregistered fields such as a client-supplied destination or to address.
2. Ask Jev one choice question using the registry's destination IDs and routing criteria. Jev evaluates the complete submission and returns a destination, probabilities for each option, and a confidence statistic.
3. Accept Jev's destination when its confidence is a valid number between 0 and 1 and meets the 0.95 threshold without rounding.
4. Send the same submission and criteria to openai/gpt-5.6-luna-fast when confidence is below the threshold, missing, or invalid, or when Jev fails or times out. The fallback uses generateText with Output.object to select a registered destination. Its valid answer determines the final assignment.
5. Return the final destination, deciding model, available Jev statistics, and model timings, along with a React Email preview. If the submitter requested an email and delivery is configured, send it through Resend.

The result includes two statistics:

• Confidence summarizes the distribution, from 0 when probability is spread evenly across destinations to 1 when it is concentrated on one destination.
• Choice probability is the probability Jev assigned to its selected destination.

The three forms

Each form has its own destinations, and every form includes a triage destination for submissions that don't contain enough evidence to pick an owner.

• A Vercel account
• AI Gateway access to typesafe-ai/jev and openai/gpt-5.6-luna-fast
• A Resend account, if you want to email routed submissions

For local development, you also need Node.js 22+, pnpm, and the Vercel CLI.

Deploy to Vercel

Deploy the template to create a copy in your GitHub account and a Vercel project. When deployment finishes, open the project URL to view the lead form at /leads.

The deployed app authenticates to AI Gateway automatically with a Vercel OpenID Connect (OIDC) token, so you don't need to configure a provider API key for routing.

• examples.ts defines the forms, destinations, and routing criteria.
• router.ts selects a destination using Jev or the fallback model.
• submission.ts validates input, renders email previews, and handles delivery.

The registry defines destinations once

lib/examples.ts defines each form's fields, sample submissions, available destinations, and routing instructions shared by both models.

These definitions determine the Zod validation schema, Jev's choice criteria, the fallback's allowed destinations, and the required keys in the recipient map.

Each destination names a team and specialty, with criteria describing which submissions it should receive:

Three parts of this question do specific work:

• The criteria keys define the allowed destination IDs for the evaluation. Object.fromEntries produces a string-keyed map, so it doesn't preserve those IDs as a literal union in the answer type. findDestination checks the returned choice against the form's registry.
• The appended sentence about untrusted evidence is the first line of defense against a submission that tries to override routing rules in its message body.
• state is a JSON object rather than a concatenated string, so the model sees field names alongside values with no serialization on your side.

Calling Jev and gating on confidence

The Jev call has a 12-second timeout that applies to the initial attempt and one SDK retry for transient failures. The application validates the returned confidence metadata with Zod before comparing it with the acceptance threshold.

• If an email wasn't requested, delivery.status is preview and nothing is sent.
• If an email was requested, deliverEmail checks for RESEND_API_KEY, a valid RESEND_FROM, and a valid inbox for every destination on the form. Incomplete configuration returns failed.
• If Resend returns a message ID, the status is accepted. If acceptance cannot be confirmed after the send attempts, the status is failed.

The routing result remains available whether delivery is skipped, accepted, or fails.

The recipient map is typed against the registry and marked server-only:

• Send up to two sequential requests with the same payload and idempotency key, preventing a retry from duplicating an accepted send if the first response is lost.
• Use the validated submitter address as replyTo.
• Render the preview and outgoing HTML from one React Email template, escaping submitted text.
• Set delivery status to accepted when Resend returns a message ID. This confirms acceptance for sending, but not inbox delivery.

Testing the policy without calling a model

lib/router.test.ts checks the routing policy by passing mock jev and luna models to routeSubmission.

These models use helpers from ai/test to return fixed answers, so the tests can verify confidence thresholds and fallback behavior without making network calls.

The tests check how the policy handles threshold values and invalid metadata:

• Accept Jev's destination at confidence 0.95, 0.98, and 1.
• Use the fallback at confidence 0.94999, even when the selected option's probability is 0.999.
• Accept confidence 0.96 with a selected-option probability of 0.7, confirming that confidence controls the decision.
• Return missing-confidence when confidence is missing, non-numeric, or outside the valid range of 0 to 1.

Another test checks that the fallback receives the same questions and state as Jev, without Jev's answer or statistics in its prompt.

These fixed responses test the application's routing rules. Evaluate the complete workflow on labeled submissions to determine whether the 0.95 cutoff produces suitable assignments.

Reading the routing result

The result panel and the RoutingDecision object it renders expose everything the policy used, so you can audit a decision after the fact.

Add a destination

1. Add an entry with an id, team, specialty, and criteria to the form's destinations array in lib/examples.ts.
2. Add the same id to routingRecipients in lib/recipients.ts, using null if it has no inbox yet. TypeScript reports the missing key until you do.
3. Update the form's instructions to specify which destination takes priority when the new and existing criteria overlap.
4. Add a test in lib/router.test.ts if the change affects how overlaps resolve.

Add a form

1. Register the form in lib/examples.ts and add its ID to ExampleId.
2. Add each destination ID to routingRecipients in lib/recipients.ts, using a receiving address or null.
3. Add the new ID to the z.enum in processSubmission in lib/submission.ts.
4. Add the form to the navigation array in app/[example]/page.tsx.

The shared components render the form and results from its registry definition.

Tune the threshold

The 0.95 threshold is a starting point. How confidence relates to routing errors depends on your destinations and your submissions, so measure it against labeled examples before relying on it:

• Test each cutoff on the same set of representative labeled submissions.
• Compare every final destination with the expected owner, including assignments made by the fallback.
• Measure routing errors, fallback frequency, response time, and cost to assess whether sending more submissions to the fallback improves the results.
• Keep confidence as the threshold input and retain the test that checks it against the selected option's probability.

Swap the fallback model

Choose an AI Gateway model that supports structured output, then update:

• The default fallback model ID in lib/router.ts.
• The RoutingDecision.model type and the model ID returned with the decision.
• The Luna-specific error message in lib/submission.ts, along with affected labels and test expectations.

Keep Jev's answer and statistics out of the fallback prompt so the replacement evaluates the submission independently. Run the mocked tests to check the routing policy, then use labeled submissions to assess the replacement's assignments. Models from different vendors can still make the same mistakes.

Troubleshooting

SUBMITTING RETURNS A SETUP ERROR ABOUT AI_GATEWAY_API_KEY

• Review the Jev x AI SDK Form Router template source to read the full routing policy, tests, and email template alongside this guide
• Read How to classify, route, and score with Jev and AI SDK to add score and boolean questions to the same experimental_evaluate request, alongside the choice type this template uses
• Follow How to automatically approve tool calls in eve with Jev to review an eve agent's proposed tool calls before execution, allowing routine actions automatically and requesting human approval for calls classified as caution
• Evaluate Jev's probabilities and choose a threshold using labeled submissions to measure routing errors and assess whether 0.95 suits your workflow
• Read What is Jev, TypeSafe AI's System One model? and When should you use Jev? to find other decisions in your application that fit a typed question
• Check the AI SDK evaluation contract for the full experimental_evaluate API, Experimental_EvaluationMockModelV4, and the rounding tolerance the SDK allows when validating distributions
• See Evaluation models on AI Gateway and the Jev model page for Zero Data Retention and No Training options, current pricing, and context limits
• Read Generating structured data in the AI SDK docs to adapt the fallback's generateText and Output.object call, for example to return a reason alongside the destination
• Follow the Resend Vercel Marketplace integration guide and the React Email docs to change how routed submissions are delivered and how the email in emails/routed-submission.tsx looks

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