# Changes to Calibre, and undo

> How an accepted change reaches your Calibre library, how it is checked, and how to take it back.

Library Hub changes your Calibre library in one way only: through the **write queue**, after you accept a change.

## The write queue

Run **Review: Open the Calibre write queue**, or open it from the **Library** tab. It shows the changes waiting, any conflicts and failures, and recent runs.

To write the waiting changes, run **Review: Write waiting changes to Calibre**.

## How a change is written

Each change is written one at a time:

1. It is written only if Calibre still holds the value the change expected. If the value changed in Calibre meanwhile, the change is a **conflict** and is not written.
2. After writing, the value is read back to check it.
3. It is logged with its run.

## Undo

A run can be undone from the queue. Undoing a run also discards its changes that are still waiting.

Other things have their own undo: a notes sync, a resync, shelves, summaries and a replaced cover.

## Jobs

Longer work runs as a job: syncing, finding covers, summaries, lookups. One writing job runs at a time.

- Open the **Library panel** (the ribbon icon, or **Library: Open the Library panel**), **Library** tab, **Activity**, to see progress, elapsed and remaining time, and the cost so far.
- A job that makes no progress for five minutes warns you. Cancel it from the Library panel.
- The status bar shows the running job, or how many things are waiting for your review.

## The one other change

When another plugin asks to read a book as an EPUB and Calibre has it only as AZW3 or MOBI, Library Hub asks you first. If you say yes, Calibre converts it and adds an EPUB to that book.

## Related

- [Fix book details](metadata-review.md)
- [Connect to Calibre](connect-to-calibre.md)