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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Before shipping a browser-based table exporter, test more than whether a file appears in Downloads. Check that CSV fields keep their boundaries, empty and irregular rows retain the intended shape, the download survives the full Blob URL lifecycle, the filename behaves as expected, and untrusted text does not become a spreadsheet formula. Run the checks in the browsers and spreadsheet applications your product supports; behavior varies across both.
1. Does a comma, quote, or line break break a cell?
Build a table with values such as Smith, Lee, He said "hello", and a cell containing a line break. Open or parse the exported CSV and confirm each value remains one field and that the multiline value does not turn into an unintended record.
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RFC 4180 describes a common CSV format in which fields containing commas, double quotes, or line breaks are enclosed in double quotes, and embedded double quotes are doubled. It describes CRLF as the record separator. These are documented conventions, not a guarantee that every CSV consumer handles files identically. See the RFC 4180 specification.
- Check that each special-character value is quoted as needed.
- Check that embedded quotes are doubled in the serialized field.
- Check that a line break inside a quoted value stays inside that field rather than being read as a new record.
- Check the exported file in the consumers your product supports, not only by inspecting the generated string.
2. Do empty or irregular rows keep the intended shape?
Test rows with empty cells at the beginning, middle, and end. Include a header row, and, if your application can produce them, rows with fewer or more cells than the header. Verify the exported field order, field count, and header policy against the table the user sees.
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RFC 4180 describes an optional header and says records should have the same number of fields. Decide how your exporter handles irregular rows—such as preserving empty fields or rejecting malformed input—and make that behavior deliberate rather than letting serialization silently shift values.
3. Does the download work in supported browsers, and is the Blob URL released safely?
Exercise the entire download from the real user action in each browser context your product supports. The anchor download attribute applies to same-origin, blob:, and data: URLs; it does not guarantee identical download handling in every browser or under every user setting. MDN documents the attribute and its constraints in the HTML <a> element reference.
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If the exporter creates a Blob URL for locally generated CSV, check that the URL is used for the download before revoking it. Revoke it afterward so the browser can release the resource; revoking it too early can disrupt access. MDN explains Blob URL use and lifecycle in its blob: URL reference.
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- Trigger export through the same click or keyboard action users will use.
- Confirm the intended file is offered or downloaded in each supported browser, accounting for that browser’s settings.
- Check that revocation occurs after the download has had access to the Blob URL.
There is no universal browser result to assume here: prompt behavior and download handling should be verified against your declared support matrix.
4. Is the suggested filename usable?
Try a requested filename with spaces and characters restricted by target filesystems. Check the suggested name and extension, then confirm the actual saved name on the platforms you support. The download value is a suggestion; browsers and filesystems may alter it. For a server-backed export variant, also test how a Content-Disposition response header affects the result. MDN covers these filename considerations in the HTML <a> reference.
5. Can untrusted text become a spreadsheet formula?
Include untrusted cells beginning with formula-like characters, then combine those values with delimiters and quotes that might make a dangerous value start a new cell. Test the file in each spreadsheet application your product supports, and include save-and-reopen if that is part of the workflow.
CSV quoting protects field boundaries; it is not, by itself, protection against formula interpretation. OWASP describes this risk as CSV/formula injection and warns that mitigations that appear effective when a file is opened may not remain safe after Excel saves and reopens it. Spreadsheet behavior and mitigation effects differ by application. See OWASP’s CSV Injection guidance.
Choose a mitigation for the spreadsheet applications in your support scope, then check both whether formula-like values are treated as data and whether the mitigation changes the underlying cell content. A tab-prefix approach, for example, has data-integrity trade-offs; no single transformation should be presented as safe for every CSV consumer.
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