# Changes to Calibre, and undo

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

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

## The write queue

Run **Books & Shelves: 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 **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, embedding, summaries, lookups. One writing job runs at a time.

- Run **Books & Shelves: Open the jobs view** 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 jobs view.
- 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, Books & Shelves 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)