Many quick CSV converters treat parsing as a regex problem: split on newlines, split on commas, zip with headers. This works on the simplest CSV files and fails immediately on real data. RFC 4180 quoting rules allow fields to contain commas, line breaks, and double quotes when surrounded by double quotes and with embedded quotes doubled. Files exported from Excel, Google Sheets, and most database tools rely on these rules. FixTools implements a stateful parser that tracks quote state across characters, recognises CRLF, LF, and bare CR as record separators, and accepts both \r\n and \n inside multi-line quoted fields. The output is the structurally correct interpretation of the input rather than a fragile string split.
Type inference at conversion time is a developer convenience that saves dozens of lines of downstream coercion. Without inference, every numeric column is a string in the JSON and consumers run parseInt or parseFloat per field. With inference, the JSON has the right types out of the gate. FixTools uses conservative column-wide promotion: if every non-empty cell parses cleanly as a more specific type, the whole column promotes, otherwise it stays as strings. This avoids the worst case of mixed types in one column where some rows have numbers and others have strings for the same key, which breaks consumers that assume a stable schema.
JSONL is the wire format of choice for streaming and big-data pipelines because each line is an independent JSON object the consumer can parse without holding the whole file in memory. FixTools offers JSONL output as an alternative to the standard JSON array. Toggle the JSONL switch and the same data emerges as one JSON object per line with no surrounding brackets and no commas between lines. This is the format expected by tools like jq with the -c flag, by BigQuery and Snowflake bulk loaders, and by many ETL frameworks.
Client-side processing is the security model developers should demand for any tool they use to handle production data extracts. CSVs from internal databases routinely contain personal information, financial records, or proprietary metrics that must not be uploaded to third-party services. FixTools runs entirely in the browser, which means the data stays on your device. You can verify by inspecting Network traffic during a conversion. For audit-sensitive workflows, this property eliminates the third-party data processor question that would otherwise need legal review.