Flycheck does not check buffers on its own. Instead it delegates this task to external syntax checkers which are external programs or services that receive the contents of the current buffer and return a list of errors in the buffer, together with metadata that tells Flycheck how to run the program, how to pass buffer contents to it, and how to extract errors.
- Supported Languages
- A complete list of all syntax checkers included in Flycheck
Like everything else in Emacs syntax checkers have online documentation which
you can access with
C-c ! ?:
C-c ! ?¶
Prompt for the name of a syntax checker and pop up a Help buffer with its documentation.
The documentation includes the name of the program or service used, a list of major modes the checker supports and a list of all options for this syntax checker.
Select syntax checkers automatically¶
Normally Flycheck automatically selects the best syntax checkers for the current
flycheck-checkers whenever it needs to check the buffer:
A list of all syntax checkers available for syntax checking.
A syntax checker in this list is a registered syntax checker.
Flycheck picks the first syntax checker from this list which exists and supports
the current major mode, and runs it over the current buffer. When the checker
has finished, Flycheck looks for the next syntax checker to run, and if there is
one, Flycheck runs the next syntax checker, and so on, until there is no more
syntax checker for the current buffer. This process repeats whenever Flycheck
needs to check the buffer according to
Under some circumstances—for instance if the syntax checker is not installed— Flycheck automatically disables syntax checkers in the current buffer and will thus not even consider them in any future checks in the current buffer.
verification buffer these syntax checkers are marked as
“disabled” just as if you had disabled them manually with
C-c ! x, and
likewise you can re-enable automatically disabled syntax checkers with
C-c ! x.
For instance, the first syntax checker for Emacs Lisp is
checks Emacs Lisp with Emacs’ own byte compiler. This syntax checker asks for
emacs-lisp-checkdoc to run next, which checks for stylistic issues in Emacs
Lisp docstrings. Thus Flycheck will first run the byte compiler and then
checkdoc in an Emacs Lisp buffer.
Select syntax checkers manually¶
Alternatively you can tell Flycheck explicitly which syntax checker to start with in the current buffer:
C-c ! s¶
Prompt for a syntax checker and use this syntax checker as the first syntax checker for the current buffer.
Flycheck may still run further syntax checkers from
flycheck-checkersif the selected syntax checker asks for it.
Flycheck will use the selected syntax checker as “entry point” for syntax checks
in the current buffer, just as if it had selected this syntax checker
automatically. It will automatically run further syntax checkers from
flycheck-checkers if the selected syntax checker asks for it.
The name of a syntax checker to use for the current buffer.
If set to a syntax checker Flycheck will use this syntax checker as the first one in the current buffer, and run subsequent syntax checkers just as if it had selected this one automatically.
If the syntax checker in this variable does not work in the current buffer signal an error.
This variable is buffer-local.
We recommend to set
flycheck-checker via directory local variables to enforce
a specific syntax checker for a project. For instance, Flycheck usually prefers
top-level directory of your project:
M-x add-dir-local-variable RET
shows the newly created entry in the directory variables. Save this buffer and
Disable syntax checkers¶
Even if you select a checker manually Flycheck may still use a syntax checker that you’d not like to use. To completely opt out from a specific syntax checker disable it:
C-c ! x¶
Prompt for a syntax checker to disable in the current buffer.
For instance if you do not care for documentation conventions of Emacs Lisp you
can opt out from
emacs-lisp-checkdoc which checks your code against these
C-c ! x emacs-lisp-checkdoc. After the next check all
checkdoc warnings will be gone from the buffer.
Internally this command changes the buffer-local
A list of disabled syntax checkers. Flycheck will never use disabled syntax checkers to check a buffer.
This option is buffer-local. You can customise this variable with
M-x customize-variable RET flycheck-disabled-checkersor set the default value in your init file to permanently disable specific syntax checkers. For instance:
(setq-default flycheck-disabled-checkers '(c/c++-clang))
will permanently disable
c/c++-clangin all buffers.
You can also disable syntax checkers per project with directory local variables.
For instance type
M-x add-dir-local-variable RET emacs-lisp-mode RET
flycheck-disabled-checkers RET emacs-lisp-checkdoc in your user emacs
directory to disable
emacs-lisp-checkdoc for all Emacs Lisp files in your
Configure syntax checkers¶
Many syntax checkers provide command line flags to change their behaviour. Flycheck wraps important flags as regular Emacs user options.
The list of supported languages includes all options for each syntax checker. You can change these options in the Customize interface under , however we recommend to use Directory Variables to configure syntax checkers per project.
- Directory Variables(emacs)
- Information about directory variables.
Some syntax checkers can additionally read configuration from files. Flycheck can find configuration files of syntax checkers and use them when invoking the syntax checker program:
Functions to call to find a configuration file for a syntax checker. Each function gets the name of a configuration file and shall return the absolute path to a file if one exists. The default value leads to the following steps:
- If the name is an absolute path, use it.
- If the name exists in any ancestor directory, use the nearest one.
- If the name exists in
$HOME, use it.
This option is an abnormal hook, see Hooks(elisp).
Flycheck takes the names of configuration files from user options defined for syntax checkers that support configuration files. Like above the list of languages also lists all supported configuration file options. You can alse change these in Customize, under , but again we recommend to use Directory Variables.
We also recommend to prefer configuration files over options as you can usually commit the configuration files to your source control repository to share them with other contributors so that all contributors can use the same configuration for syntax checking and linting.
Change syntax checker executables¶
Flycheck normally tries to run syntax checker tools by their standard name from
exec-path. Sometimes, though, you need to use a different version of a tool,
or probably don’t even have a tool available globally—this frequently occurs in
installed into a local
Prompt for a syntax checker and an executable file and make Flycheck use the executable file for the syntax checker in the current buffer.
Internally this command sets a variable named
checkeris the name of the syntax checker entered on the prompt, e.g.
Flycheck defines these executable options for every syntax checker that runs an external command. You can change these variables with directory variables or set them in custom Emacs Lisp code such as mode hooks.
- Directory Variables(emacs)
- Information about directory variables.