Token costs

FileConcat has output controls that change how much of your model's context window the output consumes. Some moves cost tokens rather than save them. This page tells you which is which, with measured numbers where they exist.

Show line numbers

FileConcat leaves line numbers off, and the current UI does not surface a toggle for them. The engine can still prefix every line of every file with its 1-based line number; that transform lives in packages/core/src/file-processing/transform.ts as addLineNumbers.

Measured against 8 representative repo files on 2026-06-07, turning it on raised the token count by 44.83 percent on average, roughly 40 to 50 percent per file. That cost is why it stays off by default: line numbers are a navigation aid for when you want the model to refer back to a specific line, not a saving.

Output style

The result screen's Format control offers XML, Markdown, and Plain. The XML style wraps each file in named tags and tends to read better for Claude. The Markdown style uses fenced code blocks and tends to read better for chat-style assistants that emit Markdown themselves. Plain concatenates the files with lightweight separators and no markup.

There is no measured token delta between the styles worth quoting here. The difference in practice is small. Pick whichever your assistant handles better.

Cross-link

For the tokenizer itself, the 1 MB self-cap, and the model selector, see Token estimation.