Frequently asked questions¶

Short answers to the things people ask most, with pointers to the chapter that covers each properly. If something is going wrong rather than merely puzzling, start with Troubleshooting.

Getting started¶

Why does nothing happen when I open a file?¶

Look at the mode line. FlyC- means no syntax checker applies to the buffer, usually because the tool is not installed. Flycheck also says so once per major mode. Press C-c ! v for the full picture: every checker that could apply, and why each one is or is not usable. See Start from the mode line.

Do I have to install the syntax checkers myself?¶

Yes. Flycheck runs the linters and compilers you already have; it does not bundle or install any of them. Supported Languages lists what each language’s checkers need.

Which checker runs when several support my language?¶

The first installed one in flycheck-checkers. Checkers that are not chained to each other do not both run, so the order decides. C-c ! v names the one that will run and lists the ones that could. To choose a different one for a buffer, use C-c ! s (flycheck-select-checker); to change it everywhere, reorder flycheck-checkers.

Can I run two linters over the same buffer?¶

Yes, by chaining them:

(flycheck-add-next-checker 'python-ruff 'python-mypy)

Both sets of errors land in the same list. See Configuring checker chains, which also covers running one only when the other found nothing serious.

Configuration¶

How do I stop a checker from running?¶

Add it to flycheck-disabled-checkers, which is buffer-local and works as a file- or directory-local variable. For one buffer, C-c ! x disables the checker at point; C-u C-c ! x re-enables one.

Why did a checker disable itself?¶

Because its tool said it could not run at all, rather than reporting findings: a missing dependency, an unreadable configuration, a linter with no config file. Flycheck names the reason and C-u C-c ! x brings the checker back. See Common issues.

How do I pass extra arguments to a checker?¶

Most checkers have a …-args option taking a list of strings, plus options for the settings people reach for most. C-c ! ? (flycheck-describe-checker) lists what a given checker accepts, and Supported Languages documents them all.

How do I point a checker at a specific executable?¶

Set its flycheck-…-executable option, which every checker has. See Change syntax checker executables.

LSP¶

I use Eglot. Why does Flycheck show nothing?¶

Eglot reports through Flymake and provides no Flycheck backend of its own. Bridge them with global-flycheck-eglot-mode. See Check buffers.

Can I use Eglot for my language server and Flycheck for a linter?¶

Yes, and both can report at once. That is the usual arrangement for something like Tailwind’s or ESLint’s server alongside the one you edit with; see Eglot and a second server together.

Why is Emacs slow in a buffer backed by a language server?¶

Some servers publish diagnostics continuously while they index or build, and each push that changes anything re-runs the check that publishes it. C-c ! v reports how many pushes arrived and how many changed something. See Troubleshooting.

Display¶

Can I see errors inline, next to the code?¶

Yes: flycheck-annotate-mode, or global-flycheck-annotate-mode everywhere. Several styles ship, from a compact message after the line to the full text underneath. See See errors in buffers.

Why do some errors have a `[fix]` marker?¶

Their checker offered a machine-applicable fix, which C-c ! f applies. A [fix?] marker means the fix has to be fetched before Flycheck knows whether there is one, as with a language server’s code actions; pressing C-c ! f asks. See Interact with errors.

Flycheck and Flymake¶

Should I use Flycheck or Flymake?¶

Both are good. Flycheck versus Flymake compares them feature by feature, without pretending to be neutral about the conclusion.

Can I run both at once?¶

You can, but you will see every diagnostic twice. flycheck-eglot-mode turns Flymake off in the buffers it manages for that reason.