Editors

Helix

What you will be able to do: edit a uf project in Helix with uf's diagnostics, hover, definitions, completion, code actions and format on write.

What you need first: uf installed, and a project with a uf.config.js.

1. Commit .helix/languages.toml

uf editor setup helix writes it. If the project already has a .helix/languages.toml that configures JavaScript, it prints the lines to add instead of writing. Or copy editors/helix/languages.toml into the project. Its substance:

[language-server.uf]
command = "uf"
args = ["lsp"]
required-root-patterns = ["uf.config.js"]

[[language]]
name = "javascript"
roots = ["uf.config.js"]
language-servers = ["uf"]
auto-format = true

[[language]]
name = "jsx"
roots = ["uf.config.js"]
language-servers = ["uf"]
auto-format = true

• language-servers replaces the default list. Helix merges a project's languages.toml into its own by language name, and a list inside it replaces the default list. ["uf"] therefore drops typescript-language-server for this project and no other. Both javascript (.js, .mjs, .cjs) and jsx need the line.
• auto-format formats on write through the server. There is no formatter line: uf fmt writes files and does not read a buffer on stdin, so the server is what formats the buffer.
• required-root-patterns starts uf only where the workspace root has a uf.config.js. In the project's own file that is always true. It matters if the file is merged into ~/.config/helix/languages.toml, which is not recommended, because there language-servers would replace the JavaScript servers of every project.

Start hx from the project root: the server reads uf.config.js from the directory it starts in.

2. Trust the project, on newer Helix

Helix 25.07.1 reads .helix/languages.toml without asking. Helix's master branch, after 25.07, reads it and starts the servers it names only once you run :workspace-trust in the project. It asks again after .helix/ changes.

Check that it worked

hx --health javascript lists uf as the language server. In a Flow file, Space + d lists only uf and flow diagnostics. Write the file, then run uf fmt --check in a terminal: they agree when the server read the project's uf.config.js. :lsp-restart after editing uf.config.js.

Checked against

The merge rules, required-root-patterns, the default servers and workspace trust were read from Helix's languages.toml, helix-loader and the book in September 2026. No Helix runs in CI.

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