---
title: "Prefill from your app session"
description: "Prefill known account values with initialData and pass identity you can trust with a server-signed respondent object."
order: 18
type: "guide"
topic: "Prefill recipes"
tags:
  - "prefill"
  - "session"
  - "respondent identity"
  - "React"
updated: "2026-07-15"
---

When someone's already signed in, don't make them retype values you know. `initialData` handles that — it's editable convenience. A signed respondent object is the separate path for identity you can actually trust.

## Sign identity on the server

```ts
// server-only helper
import { createHmac } from "node:crypto";

export function filloRespondent(user: { id: string; email: string; name: string }) {
  const hash = createHmac("sha256", process.env.FILLO_IDENTITY_SECRET!)
    .update(user.id)
    .digest("hex");

  return { ...user, hash };
}
```

## Pass identity and initial values

```tsx
"use client";

import { FilloForm } from "@usefillo/react";

export function AccountFeedback({ user, respondent }) {
  return (
    <FilloForm
      formId="account-feedback"
      respondent={respondent}
      initialData={{ email: user.email, account_name: user.accountName }}
    />
  );
}
```

Generate `respondent` in a server route or Server Component and pass only the result into the client. The identity secret must never reach browser code.

## Know what wins

Explicit `initialData` and anything the person has already typed win over URL parameters. Saved-progress restore and verified update-in-place can bring back a later snapshot. Treat prefilled visible fields as editable unless your custom UI shows a separate, server-owned account label.

Use the signed respondent ID for identify-based response limits, cross-device draft restore, and trustworthy account attribution. Don't infer identity from a prefilled email field.

## Try it

[Start with a prompt](/start?from=guide-prefill-from-app-session) and your coding agent builds the first form, staged for your review — or [open the editor](/new).

## Related

- [Custom layout example](/examples#custom-layout): Compare a default form with an application-owned account surface.
- [Respondents and identity](/docs/respondents): Configure the full server-signed identity contract.
- [Save and resume](/docs/save-and-resume): Restore a verified person's draft across devices.
- [Response limits](/docs/response-limits): Keep or update one standing response per account.