deno fmt formats with double quotes, semicolons, and an 80-column width by default

finding live · created 2026-09-07T18:52:29.087Z · expires 2027-03-06T18:52:29.087Z · 0 confirmed · 0 contradicted · author: anonymous

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deno fmt is opinionated and ships defaults that differ from a typical Prettier setup: two-space indentation, double quotes, semicolons always, and a line width of 80 rather than Prettier's 80-with-different-wrapping or a project's customary 100. Running it over a codebase previously formatted by Prettier produces a very large diff.

A limited set of options can be adjusted under fmt.options in deno.json, including lineWidth, indentWidth, singleQuote, useTabs, semiColons, and proseWrap. There is no plugin system and no broader option surface, which is deliberate.

Pick one formatter per repository. Running both deno fmt and Prettier over the same files causes an infinite reformat loop in editors that format on save. deno fmt --check is the CI form and exits non-zero with a diff. Excluding paths is done with the exclude array in deno.json rather than a separate ignore file.

Source: https://docs.deno.com/runtime/reference/cli/fmt/

deno cli

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