Quick Answer
Excel files become corrupted when the underlying ZIP structure (all .xlsx files are ZIP archives) is damaged, when a write operation was interrupted, or when a file was partially downloaded or transferred. Excel's built-in "Open and Repair" recovers some structural errors but discards data it can't parse — often losing entire sheets. Browser-based repair reads the raw file bytes, reconstructs the XML content from the ZIP archive, and extracts every recoverable row and formula without discarding data prematurely.
What is Excel file repair? Excel file repair reconstructs the ZIP archive and XML content of a damaged .xlsx file to extract cell data, formulas, and sheet structure — recovering rows that Excel's built-in Open and Repair discards.
What Your Excel Error Messages Actually Mean
"Excel found unreadable content" — The file's XML is malformed or a ZIP entry is damaged. Excel is offering to discard the problem sections. Clicking "Yes" recovers what it can — often losing entire sheets or named ranges.
"The file is corrupt and cannot be opened" — Excel can't read the file's ZIP header or central directory. The file may be truncated (incomplete download), have a byte-level corruption, or have been renamed from a non-Excel format.
"We found a problem with some content" — A specific XML section failed schema validation. Usually recoverable — Excel can often open the file after removing the offending element (often a chart, pivot table, or complex formula).
"File format or extension is not valid" — Either the file is not actually an Excel file (wrong extension), or the ZIP structure is so damaged Excel can't identify the format at all.
"Excel cannot open this file. The file format or file extension is not valid" — The file extension doesn't match its content. A file saved as .xlsx that's actually a .csv or .xls will trigger this.
Fast Fix (90 Seconds)
If your Excel file just stopped opening:
- Try Excel's built-in repair first — File → Open → Browse → select file → click the dropdown arrow on Open → "Open and Repair"
- If that fails or loses sheets, open Excel Repair Tool
- Upload the corrupted file — it processes locally in your browser
- Review what was recovered — sheets, rows, formulas, named ranges
- Download the repaired file
Each repair method was tested against intentionally corrupted .xlsx files of varying damage types, March 2026.
TL;DR: Excel files (.xlsx) are ZIP archives containing XML files. Corruption occurs when the ZIP structure, the XML content, or both are damaged. Excel's built-in repair prioritizes file integrity over data recovery — it will discard damaged sections rather than attempt partial extraction. Browser-based repair tools take the opposite approach: extract every readable XML fragment, reconstruct the workbook structure, and preserve as many rows and sheets as possible even when portions of the file are unreadable. Use Excel Repair Tool when Excel's own repair fails or loses data you need.
Table of Contents
- What Your Excel Error Messages Actually Mean
- Fast Fix (90 Seconds)
- Why Excel Files Get Corrupted
- How to Repair a Corrupted Excel File — Step by Step
- Recovery Strategies by Corruption Type
- Preventing Future Corruption
- Additional Resources
- FAQ
Your quarterly close report is due in two hours. The Excel file with three months of transaction data — 47,000 rows across four sheets — won't open. Excel throws "The file is corrupt and cannot be opened." You try Open and Repair — Excel opens a partial file with one of the four sheets. The other three sheets are gone. The sheet that did open is missing 800 rows.
Your backup is two weeks old. The person who last edited the file is on a flight. The file was last saved successfully two days ago according to the timestamp.
This is a recoverable situation. The data is almost certainly still in the file — corruption rarely destroys the raw data, it damages the structural metadata that tells Excel how to read the data. A repair tool that reads the raw file structure can often recover what Excel's built-in repair discards. For the full breakdown of Excel file size and architecture issues, see our Excel row limits and large file solutions guide. If your file opened but is missing data, see how to compare two Excel files to find what changed.
Methods That Seem Like They Should Work (But Don't)
Excel "Open and Repair"
Excel's built-in repair prioritizes file integrity over data recovery — it discards any section it can't parse cleanly rather than attempting partial extraction. Symptoms of failure: file opens with fewer sheets than expected, row counts lower than the source, formulas replaced with #REF! errors, or pivot tables missing their data source.
Changing the file extension (e.g., .xlsx to .zip)
This is the first suggestion in most forum threads. It works for manually removing a specific damaged element (like a corrupt chart) but does nothing for ZIP-level corruption or XML-level damage. If the file won't open, renaming the extension won't help.
Opening in LibreOffice Calc or Google Sheets These applications are more forgiving than Excel with some XML schema violations — worth trying. But they share the same fundamental limitation: they won't open files with severe ZIP-level corruption and will silently drop sheets with XML they can't parse.
Online repair tools that upload your file Services like Stellar Online, Aspose, EaseUS, and OfficeRecovery upload your file to their servers for repair. For files containing financial data, HR records, or any PII, this creates data exposure risk. All processing happens on their infrastructure — not on your machine.
VBA macro extraction ("ChDir" method) Requires the file to open at least partially in Excel. Fails on the corruption cases where the file won't open at all. Also limited to data extraction only — doesn't repair structural damage.
Why Excel Files Get Corrupted
Excel files (.xlsx) are ZIP archives containing XML files. The ECMA-376 Office Open XML specification, Part 1 §12 defines the structure: a workbook.xml file, individual sheet XML files (xl/worksheets/sheet1.xml), a styles definition, and a shared strings table. Each of these is a ZIP entry — damage to any one entry can make Excel refuse to open the entire file.
Corruption happens at three levels.
ZIP-level corruption damages the archive structure itself — the central directory, local file headers, or the data entries. This is usually caused by interrupted writes (power loss, crash during save, network drive disconnection) or incomplete file transfers. Excel may not be able to open the file at all.
XML-level corruption damages the content of one or more XML files inside the archive. The ZIP opens correctly, but one sheet's XML has malformed tags, invalid characters, or schema violations. Excel opens the file but discards the corrupted sheet or section.
Formula and reference corruption occurs when named ranges, external references, or formula definitions point to locations that no longer exist. The data is intact but formulas return errors and Excel may refuse to calculate the workbook.
Browser-based repair addresses all three levels by reading raw bytes from the ZIP, reconstructing damaged XML where possible, and extracting cell values even when formula context is lost.
How to Repair a Corrupted Excel File — Step by Step
Step 1: Try Excel's built-in repair first
Before using a third-party tool, attempt Excel's native repair. This works for minor XML schema issues and often recovers the file without needing anything else.
- Open Excel
- Go to File → Open → Browse
- Locate your corrupted file but don't open it normally
- Click the dropdown arrow on the Open button (bottom right of the dialog)
- Select "Open and Repair"
- Choose "Repair" when prompted
If this recovers all your sheets and data, you're done. If it opens a partial file or loses sheets, proceed to Step 2.
Symptoms that tell you Excel's built-in repair didn't fully work: Fewer sheets in the repaired file than in the original. Row counts significantly lower than expected (check against any backup, source system, or email the file was originally sent from). Formulas that were previously correct now show #REF! errors throughout. Pivot tables present but showing "Field not found" or empty. Named ranges returning #NAME? errors. Any of these indicate data was silently discarded during repair.
Step 2: Check what Excel's repair recovered
When Excel's built-in repair opens a partial file, note which sheets are missing and approximately how many rows were recovered on the sheets that did open. This tells you the scope of what needs to be recovered.
Step 3: Load the file into Excel Repair Tool
Open Excel Repair Tool in your browser. Upload the original corrupted file — not the partially-repaired version Excel created. The tool reads the raw file bytes directly.
The tool displays an analysis of the file's ZIP structure: which sections are intact, which are damaged, and which data fragments are recoverable.
Step 4: Review the recovery report
The tool shows a sheet-by-sheet breakdown:
- Fully recovered — sheet XML is intact, all rows and cells are readable
- Partially recovered — sheet XML has errors, but most rows were extracted before the damage point
- Structure only — sheet exists in the workbook index but XML is missing or unreadable; no row data recovered
- Formula degraded — cell values recovered but formulas replaced with their last-calculated values
Step 5: Download the repaired file
Download the recovered workbook. Open it in Excel and verify the data. Check row counts against any backup or source system — this tells you how much was recovered versus lost.
Recovery Strategies by Corruption Type
"The file is corrupt and cannot be opened" — ZIP-level damage
This is the most severe corruption. The ZIP archive header or central directory is damaged and Excel can't even begin to read the file.
What to try:
- Run the file through Excel Repair Tool — it can reconstruct ZIP headers from the local file headers even when the central directory is gone
- Try opening the file as a ZIP in 7-Zip or WinRAR — if individual XML files are visible, extract them manually and reconstruct the workbook
- Check if OneDrive, SharePoint, or your network drive has an older version cached — version history is often the fastest recovery path
"Excel found unreadable content" — XML-level damage
The ZIP opened but one or more XML files inside are malformed. Excel is offering to remove the damaged sections.
What to try:
- Click "Yes" to Excel's repair prompt — accept the repair and check which sheets survived
- For missing sheets, run the original through Excel Repair Tool to extract what Excel discarded
- If the problem is a specific element (chart, pivot table, conditional formatting), you can manually edit the XML inside the ZIP to remove just that element
"We found a problem with some content" — Schema validation failure
A specific XML element fails Office Open XML schema validation. Common causes: an unsupported formula, a malformed chart definition, or a named range pointing to a deleted sheet.
What to try:
- Accept Excel's repair and check if the content that was removed is critical
- If it is, the damaged element is usually identified in the repair log (Document Recovery pane after repair) — repair that specific element manually
File from a crashed or interrupted save
If Excel or your computer crashed during a save operation, the file may be truncated — complete up to the point where the crash occurred, then empty.
What to try:
- Check Excel's AutoRecover folder — Excel saves temporary recovery files every 10 minutes by default. Location:
%AppData%\Microsoft\Excel\ - If the AutoRecover file exists, it may have the most recent complete save state
Edge Cases That Complicate Excel Repair
Partially written files (truncated) If Excel crashed mid-save, the file may be valid up to the point of the crash and then empty. The ZIP central directory — written at the end of the file — may be missing entirely. The file appears corrupt but the data up to the crash point is intact in the local file headers. Recovery tools that read local headers (not just the central directory) can extract this data.
Shared workbook corruption Excel's "Shared Workbook" feature (legacy multi-user editing) stores change history and user data in separate XML sections. Corruption in the shared workbook metadata causes the file to open in a broken state even when the sheet data is intact. Removing the shared workbook attributes from the XML often restores normal function.
Large file corruption at row boundaries
For very large sheets (500K+ rows), Excel breaks the sheet XML into multiple <sheetData> chunks. Corruption at a chunk boundary truncates the recoverable row count at that boundary — rows after the corrupted chunk are unrecoverable even if their XML is intact.
Corrupt named ranges
Named ranges in workbook.xml that reference deleted sheets or invalid cell addresses cause formula errors throughout the workbook but don't prevent it from opening. The symptom is widespread #REF! errors on formulas that were previously correct. Removing or fixing the named range definitions resolves this without data loss.
Password-protected cells (not file-level) Cell-level protection locks cells from editing but doesn't encrypt the underlying data — the XML is readable. File-level password protection (encryption) uses AES-256 and the data is genuinely unreadable without the key. These are different and require different approaches.
Corrupt pivot cache
Pivot tables store a cached copy of their source data in xl/pivotCache/pivotCacheDefinition.xml. Corruption here causes pivot tables to show error states even when the source data sheet is intact. Repair tools can often recover the source data sheet while leaving the pivot table in a broken state.
Preventing Future Corruption
Most Excel file corruption is preventable. Three practices eliminate the majority of corruption incidents.
Save to local storage before editing. Files on network drives, SharePoint, or OneDrive are vulnerable to corruption if the network connection drops during a save. Copy the file locally, edit, save locally, then copy back.
Enable AutoSave and AutoRecover. In Excel: File → Options → Save → set AutoRecover interval to 5 minutes and confirm the AutoRecover file location. Per Microsoft Excel documentation, AutoRecover saves a copy every interval, giving you a fallback if the file becomes corrupted.
Keep a versioned backup. Before any major edit to an important file, save a copy with a date stamp. This takes 10 seconds and eliminates the worst-case scenario entirely.
Additional Resources
Microsoft Documentation:
- Repair a corrupted workbook — Microsoft Support — official Excel repair options and limits
- Recover your Office files — Microsoft Support — AutoRecover configuration and file locations
File Format Specification:
- ECMA-376: Office Open XML File Formats — official .xlsx ZIP and XML structure specification
- SheetJS Community Edition documentation — Excel file parsing for browser-based repair
Technical References:
- MDN: File API — browser-native file reading without upload