Check CSV cells before opening them in a spreadsheet.

Choose a small comma-delimited CSV or paste text. The checker reports common ASCII and full-width formula markers, plus leading tab or line-break controls. Everything runs in this browser tab.

Why these cells are flagged: spreadsheet programs can interpret formula-like values when a CSV is opened. This conservative check also flags ordinary negative numbers such as -10; review context before changing data. It recognizes = + - @, the full-width forms ＝ ＋ － ＠, and a leading tab, carriage return or line feed.

Limits: 5 MB, 10,000 data records, 100 columns and comma-delimited CSV only. This tool reports locations and short previews. It does not change the source, create a sanitized file, execute formulas, prove exploitability or replace a security review. Spreadsheet products differ, and quoting alone may not remain protective after a file is saved and reopened.

References: OWASP CSV Injection describes formula-start characters, separator boundaries and spreadsheet-specific trade-offs. MITRE CWE-1236 documents improper neutralization of formula elements in CSV output.