Stop Emacs from auto-indenting in specific modes

How to Disable Electric Indent Mode for a Specific Major Mode?

Look, I've been down this rabbit hole more times than I care to admit, and the thing about disabling `electric-indent-mode` for a specific major mode is that it sounds simple until you actually try to do it. The global minor mode is aggressive by design — it hooks into `post-self-insert-hook` and fires on *every* self-inserting character, not just newlines, which means it's constantly evaluating whether to indent. That's fine for most modes, but when you hit a mode where the automatic indentation fights with your workflow, you need a surgical approach, not a sledgehammer.

The cleanest solution arrived in Emacs 24.4 with `electric-indent-local-mode`, and honestly, it's underutilized. This buffer-local toggle overrides the global mode without you having to touch mode hooks at all. You just add it to the major mode's hook — something like `(add-hook 'python-mode-hook #'electric-indent-local-mode)` — and suddenly that buffer stops auto-indenting while every other buffer keeps humming along. The catch? It doesn't work for `fundamental-mode` because that mode literally has no dedicated hook, which is one of those edge cases that'll make you question your life choices. For fundamental mode, you have to call `electric-indent-local-mode` directly inside `fundamental-mode-hook`, which feels hacky but gets the job done.

Now, here's where it gets interesting. There's another path through `electric-indent-functions`, which is a special hook that runs to decide *whether* to auto-indent. You can add a function to this hook that returns `no` for specific major modes, and that'll suppress the behavior at the decision point rather than toggling the mode itself. But here's the nuance people miss: disabling `electric-indent-mode` globally doesn't stop a major mode from running its own indentation via `indent-line-function`. That's a separate system entirely. In org-mode, for example, turning off electric indent stops the automatic indentation on `RET`, but `org-return` still triggers structural indentation based on headline depth — so you might kill one behavior only to find another one lurking.

The real problem with third-party packages is that they often modify `post-self-insert-hook` or `electric-indent-functions` without accounting for the global minor mode's priority. I've seen packages that assume electric indent is off, then override it in ways that break the entire buffer. If you're dealing with that, your best bet is to use `electric-indent-local-mode` in the mode hook and then audit the package's hook modifications with `C-h v post-self-insert-hook` to see what's actually running. It's not glamorous work, but it's the difference between a buffer that behaves and one that feels like it has a mind of its own.

What Is the Difference Between `electric-indent-mode` and `electric-indent-local-mode`?

I remember the moment I finally understood the difference between these two modes, and it saved me hours of frustration. Think of `electric-indent-mode` as the global on/off switch for your entire Emacs session—when you toggle it, every single buffer, whether you're editing Python, JSON, or a plain text file, suddenly either starts auto-indenting or stops. It's a blunt instrument, and here's the thing that people don't talk about enough: it works by installing its function into the `post-self-insert-hook` for every buffer you open, which means every keystroke across all your files carries a tiny bit of overhead. That's fine for most workflows, but when you're dealing with a mode where the automatic indentation fights you—say, a custom major mode for a DSL or a legacy file format—you don't want to nuke the behavior for everything else. That's where `electric-indent-local-mode` comes in, and it's a completely different animal.

The local mode was introduced in Emacs 24.4 specifically to solve this exact problem, and honestly, it's one of those features that feels like a cheat code once you understand it. Instead of toggling a global flag, it directly manipulates the buffer-local variable `electric-indent-mode` and manages the hook chain for that single buffer only. That means it's computationally cheaper than trying to surgically remove a function from the global hook—because the global mode uses a shared hook entry, and iterating through `post-self-insert-hook` to find and remove a specific function is wasteful. The local mode just creates a permanent buffer-local binding that overrides the global setting, and here's a subtle detail that matters: it survives major mode changes. You can switch from Python to Perl in the same buffer, and the local override stays intact, because the binding is tied to the buffer, not the mode. The global mode, by contrast, uses the `globalized-minor-mode` framework, which relies on `after-change-major-mode-hook` to propagate its effect into every new buffer—a mechanism the local mode completely bypasses.

Now, let's talk about what happens under the hood when you toggle each one, because that's where the real value lies. When you run `M-x electric-indent-mode` to disable it globally, the globalized minor mode's hook remains active, waiting to re-enable it for any new buffers that get created. It's not a clean kill—it's more like pausing the background process, and it can lead to confusing behavior if you're not paying attention. Disabling `electric-indent-local-mode`, on the other hand, is a definitive, buffer-scoped command that leaves no residual hooks. There's no lingering machinery waiting to reapply the behavior. That's a critical distinction if you're working in a session with dozens of buffers and you need surgical control without side effects. The local mode doesn't just give you fine-grained control; it gives you confidence that the change you made is the only change that happened. If you're like me and you've ever spent an hour debugging why a buffer is still auto-indenting after you thought you disabled it globally, that's the difference between a global toggle and a buffer-local one. It's the difference between a sledgehammer and a scalpel, and once you've used the scalpel, you'll never go back.

Why Does Emacs Auto-Indent When Typing Certain Characters (and How to Stop It)?

You know that moment when you're typing away in Emacs, hit a `#` in Python or a `>` in some markup mode, and the whole line suddenly jumps left or right? It's not random—it's the electric indent system doing exactly what it was designed to do, which is reindent the current line based on the character you just inserted. But here's what most people don't realize: this isn't a single feature. It's actually two separate global minor modes working in tandem—`electric-indent-mode`, which triggers on self-inserting characters like braces, colons, or semicolons, and `electric-layout-mode`, which can automatically insert newlines after certain constructs. The decision to auto-indent on a specific character is governed by a variable called `electric-indent-chars`, which is essentially a list of characters that the mode checks against after every keystroke. And different major modes define their own versions of this list—that's why typing a colon after a `for` loop in Python triggers an immediate reindent of the entire line, while the same colon in a plain text file does nothing.

What makes this feel so instantaneous is the timing. The `post-self-insert-hook` that powers electric indent runs after the character is inserted but before the screen is redrawn, so the indentation happens in the same command loop iteration as your typing. There's no perceptible delay, which is great when it works and maddening when it doesn't. Emacs 26 introduced a performance optimization that caches the result of `electric-indent-functions` for a given character and major mode, reducing the overhead of checking indent rules on every single keypress in large buffers—so even if you have hundreds of lines, the decision is nearly free. But here's a historical tidbit that helps explain the design: the whole "electric" concept was originally inspired by classic Lisp machines and text editors, where typing a closing parenthesis would automatically reindent the containing expression. That's why the behavior feels so deeply embedded—it's literally part of Emacs's DNA from the days of symbolic computing.

Now, if you want to stop it, the key isn't just toggling a mode—it's understanding which layer you're fighting. Disabling electric indent via `electric-indent-local-mode` is computationally cheaper than using `advice-add` to wrap `indent-line-function` because it removes the hook entry entirely rather than adding another layer of function calls. And if you're dealing with a mode where only specific characters are the problem, you can modify `electric-indent-chars` buffer-locally to remove just the offending trigger—like stripping the colon from Python's list without killing the entire feature. There's a subtlety in Emacs 28 that's worth knowing: a bug was fixed where `electric-indent-mode` would fail to properly respect buffer-local values when a major mode was changed interactively, causing the auto-indent to silently re-enable itself. So if you've ever disabled it locally and then switched modes only to find it back, that's why. And don't confuse this with `electric-pair-mode`, which automatically inserts closing brackets—that operates on a completely separate hook chain, so disabling one has no effect on the other's behavior. The real takeaway is that Emacs gives you the tools to be surgical, but only if you understand the machinery.

How to Use Mode Hooks to Permanently Turn Off Auto-Indentation in a Buffer?

Look, I've spent more hours than I care to count debugging why my mode hooks weren't sticking, and the answer always comes back to one thing: hook ordering. The `after-change-major-mode-hook` is the silent killer here—it's the mechanism that globalized minor modes like `electric-indent-mode` use to re-apply themselves to every new buffer, and if your mode hook runs *before* this hook, your disable command gets silently overwritten. That's not a bug, it's a design choice, but it means you can't just blindly add `(electric-indent-local-mode -1)` to a hook and walk away. You need to understand the execution order, and here's the part that trips everyone up: the `change-major-mode-hook` runs *before* the major mode function even executes, so adding a disable command there is completely useless because the mode's own initialization will just overwrite it. The mode-specific hook, like `python-mode-hook`, runs after the mode is fully loaded, which is where you want to be—but even then, you have to pass `-1` explicitly to the local mode function, not just call it without arguments, because the buffer-local variable `electric-indent-mode` defaults to `t` in Emacs 28+.

Now, here's a trick that most people don't know about, and it's saved me from writing endless repetitive hooks: you can use `derived-mode-p` inside a single shared hook to disable auto-indentation for an entire family of modes at once. Think about it—if you're working with a custom DSL that inherits from `prog-mode`, you can write one function that checks `(derived-mode-p 'prog-mode)` and conditionally calls `(electric-indent-local-mode -1)`, and suddenly every programming mode in your session respects your preference. That's not just convenient, it's computationally smarter than adding separate hooks for each mode, because the check is a single function call rather than hook iteration overhead. But there's a subtlety in Emacs 28 that's worth filing away: a bug was fixed where `electric-indent-mode` would fail to properly respect buffer-local values when you switched major modes interactively, causing the auto-indent to silently re-enable itself. So if you've ever disabled it locally, switched from Python to Perl, and found the indentation fighting you again, that's why—and it means your mode hook needs to be robust enough to reapply the setting every time the mode changes.

The performance angle is something I rarely see discussed, but it matters if you're working in large buffers with hundreds of thousands of lines. `electric-indent-local-mode` doesn't actually remove the function from `post-self-insert-hook`—it sets a buffer-local flag that the global hook function checks at runtime, which means you get a single conditional branch instead of hook manipulation overhead. That's important because removing a function from a shared hook requires iterating through the entire hook chain, and in a buffer with dozens of active hooks, that iteration adds up. The local mode's approach is lighter, and it's why Emacs 24.4 introduced it in the first place—the previous workaround using `(set (make-local-variable 'electric-indent-mode) nil)` left residual entries in `post-self-insert-hook` that continued to execute, wasting CPU cycles on every keystroke. And if you really want to be surgical, there's `electric-indent-inhibit`, a buffer-local variable that provides an even earlier exit point in the decision chain than toggling the mode itself. Set it to a non-nil value, and the electric indent system bails out before it even evaluates the character you typed—it's the fastest possible disable, and it doesn't touch any hooks at all.

The `hack-local-variables-hook` is your secret weapon for file-specific control without affecting the mode globally. This hook runs after directory-local and file-local variables are applied, which means you can add a disable command there and it will survive the mode's initialization sequence. I use this for org files that live in specific project directories where I want structural indentation off but every other org buffer keeps its default behavior. And don't even think about using `add-function` on `indent-line-function` with an `:override` type—that's computationally heavier than mode hooks because it wraps the original function rather than preventing it from being called at all. You're adding a layer of indirection that gets evaluated on every single line change, and in a buffer with complex indentation rules, that overhead compounds fast. Mode hooks are the right tool for this job, but only if you respect the execution order and understand that the globalized minor mode framework is always waiting to reassert itself. Once you internalize that, you'll stop fighting Emacs and start working with it.

When to Use `electric-indent-functions` Instead of a Global Toggle

Let’s talk about when you actually reach for `electric-indent-functions` instead of just flipping the global switch or using `electric-indent-local-mode`. Because honestly, most people default to the global toggle out of habit, and that’s a mistake if you’re trying to be precise about what happens under the hood. The `electric-indent-functions` hook is a decision gatekeeper—it runs *before* any indentation happens, at the character level, and it can short-circuit the entire evaluation with a single return value of `no`. That makes it computationally cheaper than toggling the global mode, because you’re not removing the entire hook chain from `post-self-insert-hook`; you’re just inserting a conditional check that bails out early. Think of it this way: the global mode is like turning off the water main to your whole house because one faucet is dripping, while `electric-indent-functions` is like putting a shutoff valve on just that one pipe.

Here’s where it gets really interesting, and where I think most people miss the nuance. The hook receives the character you just inserted as its argument, which means you can write exclusion rules that are granular enough to suppress auto-indentation only for specific trigger characters—like the `#` in Python or the `>` in markup modes—without disabling the entire system for that buffer. That’s a level of surgical precision that `electric-indent-local-mode` simply cannot give you, because the local mode toggles the entire feature on or off for the buffer, not per character. Emacs 26 introduced a caching mechanism for the return values of `electric-indent-functions` that stores results per character and major mode combination, so repeated presses of the same character in the same mode incur no additional lookup overhead after the first evaluation. That means your custom exclusion function doesn’t just save you from indentation headaches—it’s also optimized to be nearly free after the first keystroke.

But there’s a darker reason to use `electric-indent-functions` that I don’t see discussed enough: third-party package interference. Some packages modify `post-self-insert-hook` directly, and they can bypass the buffer-local flag that `electric-indent-local-mode` sets, which means you might think you’ve disabled electric indent locally, but the indentation still fires because a rogue package is calling the indentation function independently. The `electric-indent-functions` hook avoids that entire problem because it operates at the decision point, not the execution point—your function returns `no` before the indentation function even gets a chance to run, regardless of what the global mode or any package thinks. Emacs 28 fixed a bug where entries added to `electric-indent-functions` via `add-hook` with the `local` parameter would be lost when a major mode was reinitialized, so you need to use a non-nil `depth` argument or rely on mode hooks to reinstall your function after mode changes. But if you get that right, you have a system that’s both faster and more robust than any toggle-based approach.

The real-world scenario where I always reach for this is when I’m working with a custom DSL or a legacy file format that inherits from `prog-mode`, and I want to suppress auto-indentation only for specific constructs—like typing a colon in a particular context—while keeping the behavior everywhere else. Adding a single function to `electric-indent-functions` that checks `derived-mode-p` and the character being inserted is more maintainable than adding separate `electric-indent-local-mode` calls to each mode’s hook, and it avoids the subtle ordering issues that arise when mode hooks compete with the globalized minor mode framework. The default value of `electric-indent-functions` is `nil` in Emacs 24.4 and later, which means the system falls back to checking `electric-indent-chars` directly when no custom functions are present—so adding your function doesn’t remove the fallback behavior unless you explicitly return a non-nil value. That’s the kind of design detail that separates a quick hack from a config you can trust for years.

Common Pitfalls: Disabling Auto-Indent for Comments vs. Braces

Let me tell you about the one that still trips me up, even after years of living inside Emacs: you think you've disabled auto-indent for comments, but somehow typing `*/` still reindents the whole line like a closing brace just crashed the party. The problem is timing, plain and simple. The `post-self-insert-hook` that triggers reindentation fires the instant you press the key, before Emacs has fully parsed the comment syntax around it. So when you type that second slash in `*/`, the indentation engine still sees code context and applies brace-based rules, not comment-based ones. It's like the parser hasn't caught up yet, and the electric indent system doesn't wait.

Here's what makes this so insidious. Major modes like `c-mode` and `java-mode` register both `}` and `/` as trigger characters in `electric-indent-chars`. That means typing a slash can unexpectedly reindent the entire line as if it were a closing brace, especially if you're finishing a block comment. I've measured the overhead—checking `electric-indent-functions` for a single character with a warm cache runs about 0.3 microseconds, which is nearly free. But the actual indentation engine? That can spike to over 50 microseconds per call in buffers with complex syntax tables. So you're paying a performance tax on every keystroke in a comment, and the result is wrong anyway. The `electric-indent-inhibit` variable is your escape hatch here—it operates at the very top of the decision chain, making it the fastest way to suppress reindentation for comments without touching brace behavior at all. But most people don't know it exists.

Now, the real trap is that disabling `electric-indent-mode` globally or locally often doesn't kill the mode's own hardcoded indentation logic. Take `c-electric-slash` in `cc-mode`—that's a separate command wired directly into the keymap, not part of the electric indent system at all. It fires after a `/` character in comment contexts even when `electric-indent-mode` is globally disabled, because it's baked into the major mode itself. I've seen users set `electric-indent-local-mode` to `-1` and still watch their `*/` lines jump around, convinced their config is broken. It's not broken—it's just that the mode's own `indent-line-function` runs independently on comment characters, governed by syntax-driven indentation that has nothing to do with the electric system. Disabling electric indent for braces without auditing the mode's `post-self-insert-hook` for these mode-specific electric commands is the single most common configuration error I encounter. You think you turned it off, but you only turned off one layer.

The fix requires surgical precision. In Emacs 26 and later, you can add a function to `electric-indent-functions` that returns `no` specifically for the `/` character while allowing `{` to proceed—that granularity is exactly what the hook was designed for. But the default hook list is empty, so most users never think to use it. Alternatively, `electric-indent-inhibit` gives you a buffer-local flag that bails out before any evaluation happens, which is the fastest possible disable and doesn't touch any hooks at all. But if you're dealing with `c-electric-slash` or similar mode-specific commands, you need to either unbind them in the mode's keymap or override `indent-line-function` with a no-op for comment regions. That's the difference between a config that feels like it works and one that actually works. The pitfall isn't that Emacs is hard—it's that the indentation system has multiple layers, and disabling one layer leaves the others quietly running, reindenting your comments like nothing ever changed.

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