If syntax checking does not work as expected there are a number of steps that you can follow to isolate and maybe fix the problem.

Common issues

First check whether your issue is one of the common setup issues and problems.

Flycheck can’t find any programs in GUI Emacs on MacOS

Try to install and configure exec-path-from-shell to make a GUI Emacs inherit the $PATH environment variable from your shell configuration.

The issue is that due to the special way MacOS starts GUI programs a GUI Emacs does not inherit the environment variables from the shell configuration so Emacs will lack some important entries in $PATH, most notably /usr/local/bin/ where Homebrew, NPM and many other package managers put binaries in.

The exec-path-from-shell works around this issue by extracting environment variables from a shell session and inject them into the environment of the running Emacs instance.

Flycheck warns about “non-zero exit code, but no errors”

Make sure that you have the latest version of the syntax checker installed, particularly if the message started appearing after you updated Flycheck.

Newer releases of Flycheck may require newer versions of syntax checking tools. For instance Flycheck might now pass a command line flag that older versions do not understand, or attempt to parse an updated output format. In these cases the syntax checker will show an error message about an unknown flag, or emit output that Flycheck does not understand, which prompts Flycheck to warn that even though the syntax checker appeared to not have successfully checked the buffer content there are no errors to be found.

If you are using the latest version then this message most likely indicates a flaw in the syntax checker definition. In this case please report a bug to us so that we can fix the issue. Please don’t forget to say that you are using the latest version!

Verify your setup

If your issue is none of the aforementioned common issues the first step is to let Flycheck check your setup:

C-c ! v
M-x flycheck-verify-setup

Show a verification buffer with information about your Flycheck Mode setup for the current buffer.

The buffer contains all syntax checkers available for the current buffer and tells you whether Flycheck would use each one and what reasons would prevent Flycheck from using a checker. It also includes information about your Flycheck and Emacs version and your operating system.

The following image shows a verification buffer:


The buffer shows all syntax checkers for the current buffer. Note that you can click on the syntax checker names to show the docstring for a syntax checker.

  • Green items indicate good configuration. In the screenshot both python-flake8 and python-pycompile exist.

  • Orange items indicate a potential misconfiguration. The screenshot shows that no configuration file was found for python-flake8 which is perfectly fine if there’s no flake8 configuration file in the project, but not so good if you’d like Flycheck to use a configuration file for flake8. The section Configuration files has more information about configuration files.

    Likewise the buffer warns you that a demo syntax checker (which is not part of Flycheck of course) isn’t registered in flycheck-checkers. If you’d like Flycheck to automatically use this syntax checker you should fix this issue by adding it to flycheck-checkers but otherwise it’s safe to ignore this warning.

  • Red items indicate bad configuration. python-pylint wasn’t found in the screenshot, so you’ll not be able to use pylint in the current buffer.

Debug syntax checkers

If a syntax checker fails although it successfully verified you need to take a closer look. Flycheck provides you with a command that lets you run a single syntax checker just the way Flycheck would run it:

C-c ! C-c
M-x flycheck-compile

Prompt for a syntax checker and run in as a shell command, showing the whole output in a separate buffer.


The current implementation this command suffers from a couple of issues, so we’d like to have a replacement in GH-854 and we could use your help! If you’d like to help out with this task please join the discussion in that issue.

The output of this command can provide you helpful clues about what’s going on. It also helps to compare the output of the command in Emacs with what happens if you run the same command in a terminal.

If all else fails…

…please do ask for help. We have many different channels, from Twitter to a chat room to StackOverflow, whatever suits you best, and we try to help you as fast and as good as possible.