calibre Comments Metadata Not Showing on Reader: How to Fix It

You add a description in calibre’s Comments field, confirm that it appears in the library, send the book to your Kindle, Kobo, e-reader, phone, or tablet, and then discover that the description is missing. This usually does not mean that calibre is broken. The most common explanation is that calibre’s library database contains the comments, but the receiving device or reading app does not display that metadata field.

Other possible causes include sending an older copy of the book, failing to resend it after editing metadata, using a format with limited metadata support, selecting the wrong format during transfer, or expecting a plugboard to copy comments into an unsupported field. Follow the tests below in order. Once a test succeeds, stop changing settings. That prevents a simple metadata-display limitation from turning into a larger calibre troubleshooting project.

1. Confirm the Symptom With a Small Safe Test

Start with one ordinary, non-protected book that you are allowed to manage. EPUB is a useful test format because calibre can read and write its metadata reliably, although the final result still depends on the reader.

1.1 Create a Unique Test Description

1. Select the book in calibre and choose Edit metadata.
2. Enter a distinctive sentence in Comments, such as CALIBRE DESCRIPTION TEST 4827.
3. Save the change.
4. Select the book and inspect the Book details panel in calibre.

If the exact sentence appears in Book details, the comment is stored in calibre’s library database. That is the first success condition. You do not need to edit the comment again.

If it does not appear, confirm that you edited the correct book record and the correct library. Users with multiple calibre libraries can easily update one record while viewing or transferring another.

1.2 Check the Book in calibre Before Testing the Device

Open the book with calibre’s E-book viewer and use its metadata command to inspect the book information. Do not expect the description to appear as a normal reading page unless the file already contains a jacket page. The viewer’s metadata display and the book’s readable content are separate things.

Next, determine what you are actually trying to fix:

• The comment is missing from calibre’s Book details panel.
• The comment is in calibre but absent from the e-book file’s metadata.
• The file contains the description, but the device does not display it.
• You expected the description to appear as a page inside the book.

These are different symptoms. If calibre displays the comment correctly but the reader does not, repeatedly downloading metadata will rarely help.

2. Understand calibre Database Metadata Versus Embedded Metadata

The distinction between database metadata and embedded metadata is central to fixing calibre comments metadata not showing on a reader.

2.1 Metadata Stored in the calibre Library

When you edit Comments, calibre records the value in its library database. This database is what calibre uses for its book list, searches, Book details panel, metadata editing, and Content server pages.

Changing that database value does not necessarily rewrite every e-book file in the library immediately. calibre normally updates metadata when a file is exported through an operation such as Send to device or Save to disk. This design avoids continually modifying book files whenever a library field changes.

If Book details shows your test sentence, the database side is working. Stop editing the library record and move to the transfer test.

2.2 Metadata Embedded in the E-book File

An EPUB, AZW3, PDF, MOBI, or other e-book file can carry some metadata internally. The fields supported, the way they are stored, and the amount of text accepted vary by format. A description embedded in the file also does not guarantee that a particular device will expose it in its user interface.

For a controlled check, use Save to disk to export a fresh copy after editing the Comments field. Add that exported file to a temporary calibre library or inspect it using an appropriate metadata tool. If the description is present in the fresh file, calibre successfully wrote the metadata and the remaining limitation is probably on the device or app.

Success means the exported file contains the new test description. At that point, stop changing calibre’s metadata sources or library settings.

2.3 Why the Reader Can Still Show Nothing

Many readers do not display comment or description metadata for sideloaded books. Some show only the title, author, cover, series, file type, or reading progress. Others maintain their own catalog database and ignore selected fields inside the book.

This is especially important with Kindle and Kobo workflows. The file can contain a description while the device interface provides no place to display it, displays descriptions only for store-managed books, or imports only certain fields. A reading app can impose similar restrictions.

If the description is present in a freshly exported file but absent on the reader, calibre is not necessarily malfunctioning. The practical solution may be a jacket page rather than another metadata setting.

3. Resend the Correct Book After Every Metadata Change

A common cause is that the device still has the copy sent before the Comments field was updated.

3.1 Use Send to Device Again

1. Connect the reader and wait for calibre to detect it.
2. Select the corrected book in the calibre library.
3. Open the menu beside Send to device.
4. If the book has several formats, choose the specific format supported by your reader.
5. Send the book and allow calibre’s transfer job to finish.
6. Eject the device safely and wait for its library scan or import process to complete.

If prompted about replacing an existing file, replace the old device copy. Alternatively, remove the old copy from the device first and then send the fresh version. Be careful to remove only the device copy, not the calibre library record.

Success means the device receives a newly transferred file and completes its import. If the description remains absent but other changed fields, such as the title, update correctly, the transfer worked and the comments field is probably unsupported.

3.2 Check Which Format Was Sent

A single calibre record can contain EPUB, PDF, AZW3, MOBI, and other formats. Editing one library record does not mean the reader will display every field from every format consistently.

Use the Book details panel to see which formats exist. Then send one format explicitly. Do not rely on the default transfer choice during diagnosis. If calibre performs an automatic conversion, review the completed job to confirm the output format.

Avoid testing five formats simultaneously. One known book, one output format, and one transfer path will produce a useful result.

3.3 Do Not Reuse an Old Email Attachment

If you deliver books by email, confirm that the attachment was generated after the metadata change. Sending a file from an old Downloads, Desktop, or export folder can reintroduce the outdated description.

Save a fresh copy to an empty folder, verify its modified time and filename, and attach that exact file. Also verify that you are sending to the intended account or device address. Email delivery services and reader platforms may process uploaded documents into another format, and their library interfaces may not display the original description metadata.

If a direct USB transfer and an emailed copy behave differently, treat them as separate delivery paths. Do not assume the same metadata survives both.

4. Check Device Support and Comments Field Limitations

The Comments field is often a rich-text description rather than a short plain-text value. It can contain paragraphs, links, basic formatting, or downloaded synopsis text. Readers that accept only a small plain-text description may omit it, truncate it, or handle it inconsistently.

4.1 Test With Plain Text

Replace the test book’s comment temporarily with two short plain-text sentences. Avoid tables, images, unusual symbols, copied web formatting, and long HTML-heavy descriptions. Resend the book.

If the short description appears, the original comment was probably too complex or too long for that format or reader. Simplify the production description while keeping the complete version elsewhere if needed.

If the short text is also missing, restore the original description and move on. There is no benefit in repeatedly shortening it when the device does not expose the field at all.

4.2 Compare the Reader’s Details Screen and Reading View

Look in the reader’s book information, details, properties, or information screen. Description metadata, when supported, normally appears there rather than on the first reading page.

If you want the description to be visible while reading, metadata alone is the wrong mechanism. Use a jacket page so the information becomes part of the book’s readable content.

4.3 Refresh the Device Catalog Carefully

Some devices import metadata into an internal catalog when a book first arrives. Replacing the file may not force every cached field to refresh. Remove the test book through the device’s normal library interface, safely disconnect or restart the reader if required, reconnect it, and send the updated copy again.

Success means the device treats the transfer as a new import. If title and cover refresh but comments do not, stop clearing caches or rebuilding libraries. The device almost certainly does not use that field for sideloaded books.

5. Use a Jacket Page When Descriptions Must Be Visible

A jacket page is usually the most dependable calibre comments metadata not showing on reader fix. Instead of relying on the device’s metadata interface, calibre inserts a readable page containing metadata near the beginning of the converted book.

5.1 Insert Metadata as a Page During Conversion

1. Select the test book in calibre.
2. Choose Convert books.
3. Select an output format that your device supports.
4. Find the conversion option named Insert metadata as page at start of book.
5. Enable it and start the conversion.
6. Open the converted format in calibre’s viewer.
7. Confirm that a metadata page containing the comments appears near the beginning.
8. Send that exact converted format to the device.

If the book is already in the desired format, calibre can convert it from that format to the same format for this controlled test. Preserve the original format in the calibre record until you have verified the result.

Success means the description is visible as an actual page in calibre’s viewer. Once that happens, the device does not need to support comment metadata. It only needs to render the book normally.

5.2 Know the Tradeoffs

A jacket page changes the book content, not merely its catalog entry. It may add an extra page after the cover and can include more metadata than you want. Review the converted book before sending it.

This method is most appropriate when the synopsis, notes, tags, or other details must travel with the file and remain visible across readers. It is less appropriate when you want a device’s native details screen to display a store-style description.

6. Check Plugboards, Custom Columns, and Metadata Sources

6.1 Plugboards Do Not Normally Target Comments

Metadata plugboards alter supported metadata fields when books are saved or sent to devices. They are useful for transforming fields such as title, authors, language, publisher, tags, and sorting values. They are not a general method for forcing the Comments field into a reader’s description panel.

If you already use plugboards, temporarily review them for the test format and device. Confirm that no template is unexpectedly replacing a supported destination field. Do not delete a working plugboard. Record its settings before disabling it for one controlled test.

Success means title and author arrive as expected. That confirms the plugboard is not blocking the transfer, but it still does not prove the device supports comments.

6.2 Custom Columns Are Separate From Standard Comments

A custom long-text column may look similar to Comments inside calibre, but it is not automatically the standard description field embedded in an e-book. A reader will not usually know what a calibre-specific custom column means.

Confirm that the text is in the standard Comments field. If the information must come from a custom column, use a deliberately designed template, catalog, or jacket workflow. Do not assume that creating a column called Description makes it equivalent to the built-in Comments field.

6.3 Verify Downloaded Metadata Before Sending

Metadata download plugins can obtain descriptions from supported sources, but results differ by title and source. After downloading metadata, open Edit metadata and read the Comments field. Confirm that the desired description was actually accepted into the book record.

Temporarily disable a third-party metadata or file-processing plugin only if the symptom began after installing or updating it. Test one book, then restore the plugin if it made no difference. Plugin changes are unnecessary when the device simply lacks description support.

7. Check the Content Server, Apps, and Network Path

The calibre Content server can show a book’s metadata in its web interface. This is useful for separating a server display issue from an e-reader catalog limitation.

7.1 Open the Book’s Details Page

Start the Content server, open it in a current browser, select the correct library, and open the test book’s details page. If the description appears there, the server can read it from the calibre library.

If you download the book from the server, remember that the downloaded file and the web details page are different layers. An app may display the server description while browsing but omit it after importing the file locally.

7.2 Check Server Display Restrictions

If standard metadata appears on the normal details page but custom fields are missing in a mobile or OPDS view, review the server’s displayed-field configuration. Restrictions on user-defined fields can hide custom columns. This generally does not explain a missing standard Comments value on a physical reader, so change server options only when the failure occurs in the server interface.

7.3 Rule Out Firewall and Network Problems Only When Relevant

A firewall, antivirus tool, or network rule can prevent a phone or tablet from reaching the Content server. It cannot normally remove one metadata field from a book already transferred by USB.

Investigate the network only if the server page fails to load, shows an old library, or cannot download the updated file. Confirm that the computer and device are on the intended network and that security software permits calibre’s server connection. If the page loads and shows the current description, the network is not the cause of the reader’s missing field.

8. Check USB, Permissions, Cloud Sync, and Source Quality

8.1 Confirm a Complete USB Transfer

The operating system should recognize the reader before calibre can transfer books correctly. Use the device’s file-transfer mode when required, connect only one supported reader during diagnosis, and wait for calibre’s device indicator before sending.

On macOS, review Files and Folders permissions if calibre reports access errors. On Windows and Linux, confirm that the device or mounted storage is writable. A successful calibre job and a visible new file on the device indicate that basic USB access is working.

8.2 Keep the calibre Library Out of Active Cloud Manipulation

Cloud-sync conflicts can produce stale files, locked metadata, or multiple copies when a calibre library is being modified from several computers. For diagnosis, close other calibre instances and pause tools that are actively changing the library folder.

Do not move or rename files inside the calibre library manually. Use calibre’s own commands to edit, save, convert, and transfer books.

8.3 Consider Source File Limitations

Malformed, unusually packaged, or poorly generated files can produce inconsistent metadata results. Create a fresh EPUB conversion from a known-good, non-protected source and test it separately. Do not use this process to bypass access controls or retailer restrictions.

If the clean file works while one particular book fails, the problem is specific to that source file. Keep the working test as evidence that calibre, the connection, and the device workflow are functioning.

9. Use calibre Logs and Debugging Tools When Needed

9.1 Read Job Details First

After conversion or transfer, open calibre’s Jobs list and view the relevant job details. Look for the selected input and output formats, destination, warnings, and errors. Job details are more useful than guessing whether the correct format was sent.

If the job completed without errors and the device received the updated file, the missing description is likely a display limitation rather than a transfer failure.

9.2 Use Conversion Debug Output for Content Problems

Conversion debug output records intermediate stages of calibre’s conversion pipeline. It is useful when a jacket page is missing, malformed, or removed during conversion. It is usually unnecessary when only the device’s native details screen lacks comments.

Enable conversion debugging, choose an empty output folder, and convert the single test book. Inspect the generated stages or provide them when requesting qualified support. Do not enable random conversion options at the same time, because that makes the result harder to interpret.

9.3 Debug Device Detection Only for Connection Failures

If calibre does not detect the reader, use Preferences, Miscellaneous, and Debug device detection. You can also use calibre-debug --debug-device-driver from a terminal or command prompt if you are comfortable running a documented command.

Device-detection output is not needed when Send to device completes normally. Use it only when the reader is missing, mounted incorrectly, ignored, or inaccessible.

10. Run a Clean Temporary Test Before Reinstalling

Reinstalling calibre rarely changes whether a reader supports descriptions. Before deleting a library, resetting a device, or changing many preferences, run a clean test.

1. Create a temporary calibre library.
2. Add one known-good, non-protected EPUB.
3. Enter a short unique comment.
4. Confirm it in Book details.
5. Save a fresh copy to an empty folder.
6. Convert a second copy with a jacket page.
7. Verify the jacket in calibre’s viewer.
8. Send only the jacketed copy to the reader.

If the jacket appears on the reader, calibre’s conversion and transfer functions are working. If the native device details still omit the description, that is a reader limitation. Stop changing calibre settings.

If the jacket is already missing in calibre’s viewer, investigate the conversion job and source file. If calibre cannot detect or write to the device, investigate USB mode, permissions, and device detection instead.

11. Quick Fix Checklist

• Confirm the text is in the standard Comments field.
• Verify the comment appears in calibre’s Book details panel.
• Use one test book with a short, unique plain-text description.
• Check the correct calibre library and book record.
• Identify the exact format being sent.
• Resend the book after every metadata change.
• Replace or remove the old device copy before retesting.
• Do not reuse an old saved file or email attachment.
• Check whether the reader supports descriptions for sideloaded books.
• Remember that plugboards do not generally map the Comments field.
• Do not confuse a custom text column with standard Comments.
• Use a jacket page when the description must be readable everywhere.
• Verify the jacket in calibre’s viewer before sending.
• Review job details if conversion or transfer behaves unexpectedly.
• Use device-detection debugging only when calibre cannot see the reader.

12. Frequently Asked Questions

12.1 Why does calibre show comments when my Kindle or Kobo does not?

calibre reads the Comments value from its library database and can write descriptions into supported files. Your Kindle, Kobo, or reading app controls which metadata fields appear in its interface. Many readers omit descriptions for sideloaded books even when the file contains them.

12.2 Do I need to convert the book after changing Comments?

Not always. Sending or saving a supported format can update embedded metadata. Conversion is required if you want calibre to insert the comments as a visible jacket page. Always verify the result in calibre’s viewer before transferring it.

12.3 Will a metadata plugboard make comments appear?

Usually not. Plugboards support a defined set of destination fields and are commonly used for title, author, tags, publisher, language, and sorting changes. They cannot force a device to display an unsupported description field.

12.4 Why did the title update but not the description?

That result strongly suggests the transfer succeeded but the reader imports only selected metadata fields. If a fresh file contains the description and the device shows the new title, stop changing USB, firewall, or library settings. Use a jacket page if the description must be visible.

12.5 Does reinstalling calibre fix missing comments on a reader?

Usually not. Reinstallation does not add metadata capabilities to a device. First run the temporary-library and jacket-page test. Reinstall only if calibre itself fails to start or its installation is demonstrably damaged.

12.6 What is the clearest sign that the problem is solved?

For native metadata, success means the reader’s details screen shows the current test description after a fresh transfer. For the more reliable jacket method, success means the description appears as a readable page in calibre’s viewer and then on the device. Once either expected result occurs, stop changing settings.