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Feature checklists make every tool look equivalent. This table leads with the three things that actually differ — what it costs you before it works, whether your files leave your device, and where the free version stops.
| DuckDB Web Shellshell.duckdb.org | DB Fiddledb-fiddle.com | Mockaroomockaroo.com | TableConverttableconvert.com | |
|---|---|---|---|---|
| What it does | Run SQL over your own CSV or Parquet file without uploading it | Run a schema and a query against real MySQL, Postgres or SQLite | Generates realistic fake test data in CSV, JSON or SQL | Converts a table between CSV, JSON, Markdown, SQL and Excel |
| What it costs you | No sign-upWorks the moment the page loads. No account, no email, no trial. | No sign-upWorks the moment the page loads. No account, no email, no trial. | Free tierA genuinely usable free tier with paid plans for volume or team features. | No sign-upWorks the moment the page loads. No account, no email, no trial. |
| Your files | Runs on your device | Runs on their server | Runs on their server | Runs on your device |
| Where it stops | Nothing persists between sessions, and very large files are limited by the browser's available memory. | Fiddles are public and short-lived, and query runtime is capped. | Free downloads are capped at 1,000 rows and 200 API requests a day. | Files over 10 MB are refused by the free web converter. |
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| Category | Data, Tables & Charts | Data, Tables & Charts | Data, Tables & Charts | Data, Tables & Charts |
| Last checked | 2026-07-29 | 2026-07-29 | 2026-07-29 | 2026-07-29 |
| Open the site | Open | Open | Open | Open |
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