Practical walkthroughs for working with CSV and Excel files as data rather than as documents — written against DuckDB running in the browser, so every example is runnable without a database or an upload.
An honest comparison. When Excel, Power Query, ChatGPT, DuckDB or a Python script is the better tool, and the one case where NoEgress wins: files you can’t upload.
Your policy bans pasting customer, payroll or patient data into ChatGPT. Here is how to ask an AI about a spreadsheet with the model running on your own computer.
Excel stops at 1,048,576 rows. Here is how to filter, pivot, clean and export files with millions of rows in your browser, without a database, code or an upload.
Run SQL on a CSV file without loading it into a database first. SELECT, GROUP BY, and JOIN examples you can run right in your browser with DuckDB.
Excel stops at 1,048,576 rows and slows down well before that. How to open, check, and query CSV files with millions of rows in your browser, with no upload.
Query .xlsx workbooks with SQL instead of nested formulas. How sheets become tables, how to fix messy headers and numbers stored as text, and how to join a sheet to a CSV.
Online CSV and SQL tools need your file on their servers. How browser-based analysis with WebAssembly avoids that, what "local" means in practice, and how to check it yourself.
Many online tools say your file never leaves your browser. Three checks anyone can run in a few minutes to see whether that’s true, and what each one can and can’t prove.
Find added, removed, and changed rows between two versions of a CSV export. A SQL approach built on a key column, plus how to ignore differences that are only formatting.
Seven quick SQL checks that catch the errors behind bad analysis: duplicate keys, wrong types, hidden nulls, impossible values, messy categories, and truncated exports.
Turn a JSON export into a table and query it with SQL. How arrays, API wrapper objects, and nested fields map to rows and columns, and how to pull out nested values.
Run DuckDB in your browser with DuckDB-WASM. Open a CSV, Excel, or JSON file and query it with full DuckDB SQL. Nothing to install, and nothing gets uploaded.
Ask questions about a CSV or Excel file in plain English. A local LLM runs in your browser on WebGPU and writes DuckDB SQL for you. No ChatGPT upload, no API key.
Remove duplicate rows from a CSV or Excel file in your browser. Match on every column or just a key, keep the first or last copy, and download the clean file.
Split one CSV or Excel file into separate files, one per region, manager or customer, in your browser. Download them all as a ZIP. No upload, no macros.
Convert between CSV, Excel (XLSX), and Parquet in your browser without uploading the file. Also opens TSV and JSON. Free, with no account and no file size cap.
Merge CSV or Excel files in your browser: stack monthly exports into one table, or bring in columns from a second file by a matching key, like VLOOKUP but faster.