> ## Documentation Index
> Fetch the complete documentation index at: https://docs.rehydra.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Rehydration

> How Rehydra restores original values in reversible workflows

Rehydration is the step that turns placeholder-based text back into its original values. It only works when the text was produced in `pseudonymize` mode and you still have the matching encryption key.

## When Rehydration Is Possible

Rehydration requires all of the following:

* The text was processed in `pseudonymize` mode
* You kept the returned encrypted `piiMap`
* You still have the correct key to decrypt that `piiMap`

If any of these are missing, rehydration cannot restore the originals.

## Basic Flow

```typescript theme={null}
import { decryptPIIMap, rehydrate } from 'rehydra';

const key = await keyProvider.getKey();
const piiMap = await decryptPIIMap(result.piiMap, key);
const restored = rehydrate(textWithPlaceholders, piiMap);
```

## What Rehydration Uses

Rehydra matches placeholders such as `<PII type="EMAIL" id="1"/>` (or custom formats like `[[PII type="EMAIL" id="1"]]`) against the decrypted map and replaces them with the original values.

This means the placeholder structure must stay intact between protection and restoration. If you used a custom `tagFormat` during anonymization, pass the same format to `rehydrate()`.

## Rehydration vs Anonymization

| Workflow       | `piiMap` exists | Originals recoverable |
| -------------- | --------------- | --------------------- |
| `pseudonymize` | Yes             | Yes                   |
| `anonymize`    | No              | No                    |

## Common Failure Modes

* Using the wrong key
* Losing the encrypted `piiMap`
* Running in `anonymize` mode instead of `pseudonymize`
* Modifying placeholder tags so they no longer match the stored mapping

## Where It Shows Up

Rehydration is part of:

* SDK workflows using `decryptPIIMap()` and `rehydrate()`
* CLI workflows using `rehydra rehydrate`
* Agent and plugin flows that restore values locally before tool execution

## Next Steps

<CardGroup cols={2}>
  <Card title="Encryption & Security" icon="lock" href="/concepts/encryption">
    Learn how `piiMap` data and keys are handled.
  </Card>

  <Card title="Anonymization & Pseudonymization" icon="masks-theater" href="/concepts/anonymization-pipeline">
    See how reversible and irreversible modes differ.
  </Card>
</CardGroup>