Dealing with Errors

Every now and then you’ll make some mistake in your code which is going to result in an evaluation error. Clojure’s errors are notorious for their complexity and CIDER takes a lot of effort to make it easier to decipher those.

Most of the time CIDER will display the errors in a dedicated buffer alongside the buffer you’re currently evaluating code in.

Use q to quickly close an error buffer.


By default, when an exception occurs, CIDER will display the exception in an error buffer using cider-stacktrace-mode. You can suppress this behavior, which causes just the error message to be output as a temporary overlay or in the echo area:

(setq cider-show-error-buffer nil)

At times, the error being displayed will originate from a bug in CIDER itself. These internal errors might frequently occur and interrupt your workflow, but you might not want to suppress all stacktrace buffers by using cider-show-error-buffer. Instead, you might only want to suppress this specific type of internal error. The stacktrace buffers provide such an option when displaying an internal error. A toggle button will be displayed with the error type’s name, and you can toggle whether this particular type of error will cause the stacktrace buffer to automatically show itself. The toggle button controls this behavior only during the current Emacs session, but if you would like to make the suppression more permanent, you can do so by customizing the cider-stacktrace-suppressed-errors variable. The buffer will also provide a direct link to the bug reporting page to help facilitate its diagnosis and repair.

Independently of the value of cider-show-error-buffer or cider-stacktrace-suppressed-errors, CIDER always generates the error buffer in the background. You can use cider-selector (C-c M-s) to visit this buffer if you decide that you need to.

There are two more selective strategies for the error buffer:

(setq cider-show-error-buffer 'except-in-repl) ; or
(setq cider-show-error-buffer 'only-in-repl)

To disable auto-selection of the error buffer when it’s displayed:

(setq cider-auto-select-error-buffer nil)

CIDER comes with a powerful solution for dealing with Clojure stacktraces. CIDER presents stack traces in a special major mode, cider-stacktrace-mode, which gives you gives you some key features:

  • the ability to filter out certain stack frames to reduce clutter

  • some handy ways to navigate to the cause of the exception

  • the ability to jump straight to code with a single keystroke


Command Keyboard shortcut Description



Move point to previous cause



Move point to next cause


M-. or Return

Navigate to the source location (if available) for the stacktrace frame



Cycle current cause detail


0 or S-Tab

Cycle all cause detail



Cycle cause #1 detail



Cycle cause #2 detail



Cycle cause #3 detail



Cycle cause #4 detail



Cycle cause #5 detail



Toggle display of Java frames



Toggle display of Clojure frames



Toggle display of REPL frames



Toggle display of tooling frames (e.g. compiler, nREPL middleware)



Toggle display of duplicate frames



Toggle display only project frames



Toggle display of all frames

Filtering Stack Frames

CIDER helps you cut through the clutter of Clojure stacktraces by allowing you to apply a list of filters using the cider-stacktrace-default-filters variable. Valid filter types include java, clj, repl, tooling, and dup. Specifying one of these filters will remove the corresponding frames from the stacktrace display. There are also "positive" filtering types (reverse filters) that specify what should be shown. The value of project, for instance, will cause only project frames to be shown, and all will force all stackframes to be shown. Note that project and all are mutually exclusive. Whichever one is first will determine the behavior if they are both present.

(setq cider-stacktrace-default-filters '(tooling dup))
;; or
(setq cider-stacktrace-default-filters '(project))

Wrapping Error Messages

Finally, CIDER can wrap error messages when they are displayed in a buffer to help improve their readability. CIDER uses cider-stacktrace-fill-column for this, which can take on three types of values:

  • nil: The error is not wrapped.

  • numeric: The error message is wrapped to the specified fill column.

  • Something truthy but non-numeric: The error message is wrapped using the value of fill-column.

The following will cause error messages to be wrapped to 80 columns, for instance:

(setq cider-stacktrace-fill-column 80)