Why did ATTSYNC reset my attribute values?

ATTSYNC rebuilds every reference from the new block definition and matches attributes by tag. An attribute whose tag was renamed has nowhere to take its old value from and goes back to its default, and attribute positions are reset to the definition. It also only works on the drawing that is open.

Do I need LISP to update a block in many drawings?

No. BlockCopy's Sync Update replaces the block definition in every target drawing and re-syncs each reference for you, with no script to write or maintain.

What happens to a value when its attribute tag was renamed?

Before anything is written, BlockCopy lists each tag that still holds values but is missing from the new definition. You choose which new tag receives those values, or discard them, and only then does it write. Values are matched by tag name, not by position.

How do I undo a sync?

With Automatic backup ticked, every drawing is copied to the backup folder first. Rollback in a drawing's details puts that drawing back, and Restore Backup does the same for drawings from any earlier run, even after the program has been closed.

What do I need to run this?

A Windows 10 or 11 PC and the drawings. AutoCAD does not have to be running. CADXChange Toolkit includes a 30-day full trial; after it, reading, scanning and previewing keep working, and writing to drawings needs a licence.

Guides/Drawing standards

ATTSYNC Cleared My Attribute Values in AutoCAD — Update a Block in Many Drawings Safely

Updated November 5, 2026

Made with BlockCopy

BlockCopy's results after updating a title block whose attribute tag was renamed, with the old and new tags mapped in six drawings

You revise the title block (add a line, tidy the layout, rename SHEET_NO to DWG_NO), redefine it, run ATTSYNC, and the drawing number on every sheet is back to its default. Or the values survive, but every attribute someone had nudged clear of a line snaps back into place.

That is ATTSYNC working as designed. It matches attributes by tag, so a value whose tag was renamed has nowhere to go and the new tag starts at its default. It also resets every attribute's position and formatting to the definition. Autodesk's own advice is not to change tags once a block has been placed. And it only works inside the drawing that is open, after the new definition has been brought into that drawing.

This guide uses the Sync Update tab of BlockCopy, part of CADXChange Toolkit, to push a revised block definition into a whole set of drawings in one run. Values carry over by tag, the values of a renamed tag are mapped to the new tag instead of being lost, and every value is read back afterwards. The example pushes a revised TITLEBLOCK, with SHEET_NO renamed to DWG_NO, into six sheets.

1. Put the revised block in one source drawing

Make the change once, in BEDIT or with BLOCK, in any drawing, and save it. That drawing is the source. Keep the block's name: Sync Update replaces a definition with a newer version of itself. Moving drawings over to a block with a different name is a different job, covered at the end.

Renamed, added and removed attributes are all fine; the next steps deal with them.

2. Pick the source block and the target drawings

Open BlockCopy and switch to Sync Update. Browse to the source drawing: its blocks are listed with their reference count and whether they carry attributes, and View shows a block's attribute list. Tick the block to push.

Click Add files and pick the drawings that use the block. They only need the old version; the new one comes from the source. Leave Automatic backup ticked: every drawing is copied to the backup folder before it is changed.

Keep attribute positions is ticked by default, so attributes someone moved by hand stay where they are. Untick it when the revision moved attributes on purpose, such as a new title block layout.

3. Map any renamed tag

Click Sync Now. BlockCopy first reads every target drawing and compares its attributes with the new definition. If a tag that still holds values is missing from the new one, here SHEET_NO, a dialog lists it before anything is written.

Choose the new tag that should receive its values (DWG_NO), or choose Discard values if that information really is gone, and click Apply and sync. Cancel leaves every drawing untouched.

4. Check the results

In each drawing BlockCopy replaces the definition and rebuilds every reference from it, carrying each value over by tag, and the values of a mapped tag over to its new tag. The list shows the result per drawing, here TITLEBLOCK: synced 1 reference(s) with Success on all six.

After saving each drawing, BlockCopy reads it back and compares the attribute values with what it held before. A drawing where something does not match is marked Failed with the details, and the rest of the batch carries on. When we mapped SHEET_NO to the wrong tag (CLIENT) on purpose, every drawing was marked Failed with 1 attribute that did not survive the sync as expected, instead of passing quietly.

Rollback in a drawing's details, or Restore Backup, puts any drawing back exactly as it was, even after BlockCopy has been closed.

5. Look at the values yourself

The quickest independent check is to read the drawings back. Add them to BlockSync's Blocks → Excel tab and extract TITLEBLOCK: the sheet now has a DWG_NO column holding A-101 to A-202, which used to be in SHEET_NO, and the revision, title, client and address are what they were.

In this example the block handles did not change either, so an Excel export made before the sync can still be written back.

Excel sheet extracted by BlockSync after the sync: the DWG_NO column holds A-101 to A-202, next to the unchanged revision and title of each drawing

If the drawings should switch to a block with a different name, such as an old logo or symbol replaced by a new one, use BlockCopy's Upgrade Version tab instead of Sync Update. It swaps the references and carries the attribute values over to the new block.

CADXChange Toolkit comes with a 30-day full trial, so you can run this on a copy of a real set first. Close the drawings in AutoCAD before you sync, because a file that is open elsewhere can be locked.

Try it on your own drawings

CADXChange Toolkit does this for a whole folder of drawings, with a preview and a backup first. The 30-day trial has every feature.

Start the free trial →

Before you start — common questions

Why did ATTSYNC reset my attribute values?: ATTSYNC rebuilds every reference from the new block definition and matches attributes by tag. An attribute whose tag was renamed has nowhere to take its old value from and goes back to its default, and attribute positions are reset to the definition. It also only works on the drawing that is open.
Do I need LISP to update a block in many drawings?: No. BlockCopy's Sync Update replaces the block definition in every target drawing and re-syncs each reference for you, with no script to write or maintain.
What happens to a value when its attribute tag was renamed?: Before anything is written, BlockCopy lists each tag that still holds values but is missing from the new definition. You choose which new tag receives those values, or discard them, and only then does it write. Values are matched by tag name, not by position.
How do I know no values were lost?: After saving each drawing, BlockCopy reads it back and compares every attribute value with what it held before. A drawing where something does not match is marked Failed with the details, and Rollback or Restore Backup puts it back exactly as it was.
How do I undo a sync?: With Automatic backup ticked, every drawing is copied to the backup folder first. Rollback in a drawing's details puts that drawing back, and Restore Backup does the same for drawings from any earlier run, even after the program has been closed.
What do I need to run this?: A Windows 10 or 11 PC and the drawings. AutoCAD does not have to be running. CADXChange Toolkit includes a 30-day full trial; after it, reading, scanning and previewing keep working, and writing to drawings needs a licence.