diff --git a/src/compiler/compile/Component.ts b/src/compiler/compile/Component.ts
index 49c60ccd6f..07c9a20f2c 100644
--- a/src/compiler/compile/Component.ts
+++ b/src/compiler/compile/Component.ts
@@ -231,9 +231,6 @@ export default class Component {
 
 			const banner = `${this.file ? `${this.file} ` : ``}generated by Svelte v${__VERSION__}`;
 
-			const legacy_dev_runtime = compile_options.dev && compile_options.version < 3.22;
-			const dev_runtime = compile_options.dev && compile_options.version >= 3.22;
-
 			const program: any = { type: 'Program', body: result.js };
 
 			walk(program, {
@@ -246,11 +243,11 @@ export default class Component {
 							} else {
 								let name = node.name.slice(1);
 
-								if (legacy_dev_runtime) {
-									if (internal_exports.has(`${name}_dev$legacy`)) {
-										name += '_dev$legacy';
-									} else if (internal_exports.has(`${name}Dev$legacy`)) {
-										name += 'Dev$legacy';
+								if (compile_options.dev) {
+									if (internal_exports.has(`${name}_dev`)) {
+										name += '_dev';
+									} else if (internal_exports.has(`${name}Dev`)) {
+										name += 'Dev';
 									}
 								}
 
@@ -290,7 +287,7 @@ export default class Component {
 				format,
 				name,
 				banner,
-				compile_options.sveltePath + (dev_runtime ? '/dev' : ''),
+				compile_options.sveltePath,
 				imported_helpers,
 				referenced_globals,
 				this.imports,
@@ -838,7 +835,7 @@ export default class Component {
 			const guard = this.get_unique_name('guard', scope);
 			this.used_names.add(guard.name);
 
-			const before = b`const ${guard} = @loop_guard(${timeout})`;
+			const before = b`const ${guard} = @loop_guard_dev(${timeout})`;
 			const inside = b`${guard}();`;
 
 			// wrap expression statement with BlockStatement
diff --git a/src/compiler/compile/index.ts b/src/compiler/compile/index.ts
index 3374626189..7b992eb712 100644
--- a/src/compiler/compile/index.ts
+++ b/src/compiler/compile/index.ts
@@ -8,7 +8,6 @@ import fuzzymatch from '../utils/fuzzymatch';
 import get_name_from_filename from './utils/get_name_from_filename';
 
 const valid_options = [
-	'version',
 	'format',
 	'name',
 	'filename',
@@ -68,7 +67,7 @@ function validate_options(options: CompileOptions, warnings: Warning[]) {
 }
 
 export default function compile(source: string, options: CompileOptions = {}) {
-	options = { generate: 'dom', dev: null, version: 3, ...options };
+	options = { generate: 'dom', dev: null, ...options };
 
 	const stats = new Stats();
 	const warnings = [];
diff --git a/src/compiler/compile/render_dom/Block.ts b/src/compiler/compile/render_dom/Block.ts
index 173fe09a34..e6ce3e2302 100644
--- a/src/compiler/compile/render_dom/Block.ts
+++ b/src/compiler/compile/render_dom/Block.ts
@@ -229,7 +229,7 @@ export default class Block {
 	}
 
 	get_contents(key?: any) {
-		const { dev, version } = this.renderer.options;
+		const { dev } = this.renderer.options;
 		let k;
 		for (k in this.chunks) this.chunks[k] = this.chunks[k].filter(Boolean);
 
@@ -403,8 +403,8 @@ export default class Block {
 					? b`
 					const ${block} = ${return_value};
 					${
-						version < 3.22 &&
-						b`@dispatch_dev$legacy("SvelteRegisterBlock", {
+						dev &&
+						b`@dispatch_dev("SvelteRegisterBlock", {
 						block: ${block},
 						id: ${this.name || 'create_fragment'}.name,
 						type: "${this.type}",
diff --git a/src/compiler/compile/render_dom/index.ts b/src/compiler/compile/render_dom/index.ts
index c83e29a3e8..abd8742f07 100644
--- a/src/compiler/compile/render_dom/index.ts
+++ b/src/compiler/compile/render_dom/index.ts
@@ -267,7 +267,7 @@ export default function dom(component: Component, options: CompileOptions): { js
 					: b`$$self.$$.on_destroy.push(@subscribe(${name}, #value => $$invalidate(${i}, ${value} = #value)));`;
 
 			if (component.compile_options.dev) {
-				return b`@validate_store(${name}, '${name}'); ${insert}`;
+				return b`@validate_store_dev(${name}, '${name}'); ${insert}`;
 			}
 
 			return insert;
@@ -342,7 +342,7 @@ export default function dom(component: Component, options: CompileOptions): { js
 		})
 		.map(
 			({ name }) => b`
-			${component.compile_options.dev && b`@validate_store(${name.slice(1)}, '${name.slice(1)}');`}
+			${component.compile_options.dev && b`@validate_store_dev(${name.slice(1)}, '${name.slice(1)}');`}
 			$$self.$$.on_destroy.push(@subscribe(${name.slice(1)}, #value => $$invalidate(${
 				renderer.context_lookup.get(name).index
 			}, ${name} = #value));
@@ -443,7 +443,7 @@ export default function dom(component: Component, options: CompileOptions): { js
 				${component.slots.size || component.compile_options.dev ? b`let { $$slots = {}, $$scope } = $$props;` : null}
 				${
 					component.compile_options.dev &&
-					b`@validate_slots('${component.tag}', $$slots, [${[...component.slots.keys()]
+					b`@validate_slots_dev('${component.tag}', $$slots, [${[...component.slots.keys()]
 						.map((key) => `'${key}'`)
 						.join(',')}]);`
 				}
@@ -562,8 +562,7 @@ export default function dom(component: Component, options: CompileOptions): { js
 		}, ${not_equal}, ${prop_indexes}, ${dirty});
 					${
 						options.dev &&
-						options.version < 3.22 &&
-						b`@dispatch_dev$legacy("SvelteRegisterComponent", { component: this, tagName: "${name.name}", options, id: create_fragment.name });`
+						b`@dispatch_dev("SvelteRegisterComponent", { component: this, tagName: "${name.name}", options, id: create_fragment.name });`
 					}
 
 					${dev_props_check}
diff --git a/src/compiler/compile/render_dom/wrappers/EachBlock.ts b/src/compiler/compile/render_dom/wrappers/EachBlock.ts
index 5b648f8ec0..e8e265dd72 100644
--- a/src/compiler/compile/render_dom/wrappers/EachBlock.ts
+++ b/src/compiler/compile/render_dom/wrappers/EachBlock.ts
@@ -172,7 +172,7 @@ export default class EachBlockWrapper extends Wrapper {
 
 		block.chunks.init.push(b`let ${each_block_value} = ${snippet};`);
 		if (__DEV__) {
-			block.chunks.init.push(b`@validate_each_argument(${each_block_value});`);
+			block.chunks.init.push(b`@is_array_like_dev(${each_block_value});`);
 		}
 
 		renderer.blocks.push(b`
@@ -341,9 +341,9 @@ export default class EachBlockWrapper extends Wrapper {
 			);
 
 		const validate_each_keys =
-			__DEV__ && b`@validate_each_keys(#ctx, ${each_block_value}, ${each_context_getter}, ${key_getter});`;
+			__DEV__ && b`@check_duplicate_keys_dev(#ctx, ${each_block_value}, ${each_context_getter}, ${key_getter});`;
 
-		const validate_each_argument = __DEV__ && b`@validate_each_argument(${each_block_value});`;
+		const validate_each_argument = __DEV__ && b`@is_array_like_dev(${each_block_value});`;
 
 		block.chunks.init.push(
 			b`const ${key_getter} = (#ctx) => ${this.node.key.manipulate(block)};`,
@@ -438,7 +438,7 @@ export default class EachBlockWrapper extends Wrapper {
 			this.updates.push(b`
 				${!has_update_method && b`const #old_length = ${each_block}.length;`}
 				${each_block_value} = ${snippet};
-				${__DEV__ && b`@validate_each_argument(${each_block_value});`}
+				${__DEV__ && b`@is_array_like_dev(${each_block_value});`}
 				let #i = ${start}, #block;
 				${for_loop(
 					each_block_value,
diff --git a/src/compiler/compile/render_dom/wrappers/Element/index.ts b/src/compiler/compile/render_dom/wrappers/Element/index.ts
index c0db934948..3eed0cb650 100644
--- a/src/compiler/compile/render_dom/wrappers/Element/index.ts
+++ b/src/compiler/compile/render_dom/wrappers/Element/index.ts
@@ -372,9 +372,7 @@ export default class ElementWrapper extends Wrapper {
 		if (renderer.options.dev) {
 			const loc = renderer.locate(this.node.start);
 			block.chunks.hydrate.push(
-				b`@add_location_dev$legacy(${this.var}, ${renderer.file_var}, ${loc.line - 1}, ${loc.column}, ${
-					this.node.start
-				});`
+				b`@add_location_dev(${this.var}, ${renderer.file_var}, ${loc.line - 1}, ${loc.column}, ${this.node.start});`
 			);
 		}
 	}
diff --git a/src/compiler/compile/render_ssr/index.ts b/src/compiler/compile/render_ssr/index.ts
index f4657324b4..0177e63069 100644
--- a/src/compiler/compile/render_ssr/index.ts
+++ b/src/compiler/compile/render_ssr/index.ts
@@ -42,7 +42,7 @@ export default function ssr(component: Component, options: CompileOptions): { js
 			if (store && store.hoistable) return null;
 			const assignment = b`${store_name}.subscribe(#v=>{${name}=#v})();`;
 			return component.compile_options.dev
-				? b`@validate_store(${store_name}, '${store_name}'); ${assignment}`
+				? b`@validate_store_dev(${store_name}, '${store_name}'); ${assignment}`
 				: assignment;
 		})
 		.filter(Boolean);
@@ -50,7 +50,7 @@ export default function ssr(component: Component, options: CompileOptions): { js
 	component.rewrite_props(
 		({ name }) =>
 			b`${
-				component.compile_options.dev && b`@validate_store(${name}, '${name}');`
+				component.compile_options.dev && b`@validate_store_dev(${name}, '${name}');`
 			}${name}.subscribe((#v)=>{$${name}=#v})()`
 	);
 
diff --git a/src/compiler/interfaces.ts b/src/compiler/interfaces.ts
index 2184beb7fb..f60eedcbd7 100644
--- a/src/compiler/interfaces.ts
+++ b/src/compiler/interfaces.ts
@@ -102,12 +102,8 @@ export interface Warning {
 export type ModuleFormat = 'esm' | 'cjs';
 
 export interface CompileOptions {
-	/* bundler */
 	filename?: string;
-	version?: number;
 	format?: ModuleFormat;
-
-	/* Component class name */
 	name?: string;
 	generate?: string | false;
 
diff --git a/src/runtime/easing/index.ts b/src/runtime/easing/index.ts
index 6f20064b84..612c8ab082 100644
--- a/src/runtime/easing/index.ts
+++ b/src/runtime/easing/index.ts
@@ -1,5 +1,3 @@
-import { dev$assert } from 'svelte/internal';
-
 export const linear = (t: number) => t;
 export const quadIn = (t: number) => t ** 2;
 export const quadOut = (t: number) => 1.0 - (1.0 - t) ** 2;
@@ -49,10 +47,9 @@ export const circOut = (t: number) => Math.sin(Math.acos(1.0 - t));
 export const circInOut = (t: number) =>
 	0.5 * (t >= 0.5 ? 2.0 - Math.sin(Math.acos(1.0 - 2.0 * (1.0 - t))) : Math.sin(Math.acos(1.0 - 2.0 * t)));
 export const cubicBezier = (x1: number, y1: number, x2: number, y2: number) => {
-	dev$assert(
-		x1 >= 0 && x1 <= 1 && x2 >= 0 && x2 <= 1,
-		`CubicBezier x1 & x2 values must be { 0 < x < 1 }, got { x1 : ${x1}, x2: ${x2} }`
-	);
+	if (!(x1 >= 0 && x1 <= 1 && x2 >= 0 && x2 <= 1)) {
+		throw new Error(`CubicBezier x1 & x2 values must be { 0 < x < 1 }, got { x1 : ${x1}, x2: ${x2} }`);
+	}
 	const ax = 1.0 - (x2 = 3.0 * (x2 - x1) - (x1 = 3.0 * x1)) - x1,
 		ay = 1.0 - (y2 = 3.0 * (y2 - y1) - (y1 = 3.0 * y1)) - y1;
 	let i = 0,
diff --git a/src/runtime/environment/index.ts b/src/runtime/environment/index.ts
index 747a496de3..04e72a1f2b 100644
--- a/src/runtime/environment/index.ts
+++ b/src/runtime/environment/index.ts
@@ -20,7 +20,7 @@ export const resolved_promise = Promise.resolve();
 export let now = /*#__PURE__*/ is_browser ? performance.now.bind(performance) : Date.now.bind(Date);
 export let raf = /*#__PURE__*/ __TEST__ ? () => {} : is_browser ? requestAnimationFrame : noop;
 export let framerate = 1000 / 60;
-raf((t1) => {
+/*#__PURE__*/ raf((t1) => {
 	raf((d) => {
 		const f24 = 1000 / 24,
 			f144 = 1000 / 144;
diff --git a/src/runtime/internal/animations.ts b/src/runtime/internal/animations.ts
index adc4cc0443..d7322db3a6 100644
--- a/src/runtime/internal/animations.ts
+++ b/src/runtime/internal/animations.ts
@@ -11,7 +11,7 @@ export interface AnimationConfig {
 
 type AnimationFn = (node: Element, { from, to }: { from: DOMRect; to: DOMRect }, params: any) => AnimationConfig;
 
-export const run_animation = Function.prototype.call.bind(function run_animation(
+export const run_animation = /*#__PURE__*/ Function.prototype.call.bind(function run_animation(
 	this: HTMLElement,
 	from: DOMRect,
 	fn: AnimationFn,
@@ -31,7 +31,7 @@ export const run_animation = Function.prototype.call.bind(function run_animation
 	);
 });
 
-export const fix_position = Function.prototype.call.bind(function fix_position(
+export const fix_position = /*#__PURE__*/ Function.prototype.call.bind(function fix_position(
 	this: HTMLElement,
 	{ left, top }: DOMRect
 ) {
diff --git a/src/runtime/internal/dev.legacy.ts b/src/runtime/internal/dev.legacy.ts
deleted file mode 100644
index 5626e7a45b..0000000000
--- a/src/runtime/internal/dev.legacy.ts
+++ /dev/null
@@ -1,109 +0,0 @@
-import { custom_event, append, insert, detach, listen, attr } from './dom';
-import { now } from 'svelte/environment';
-let inited;
-export function add_location_dev$legacy(element, file, line, column, char) {
-	element.__svelte_meta = {
-		loc: { file, line, column, char },
-	};
-}
-export function dispatch_dev$legacy<T = any>(type: string, detail?: T) {
-	if (!inited && `__SVELTE_DEVTOOLS_GLOBAL_HOOK__` in window) {
-		inited = true;
-		throw new Error(`You must specify the version`);
-	}
-	document.dispatchEvent(custom_event(type, { version: __VERSION__, ...detail }));
-}
-
-export function append_dev$legacy(target: Node, node: Node) {
-	dispatch_dev$legacy('SvelteDOMInsert', { target, node });
-	append(target, node);
-}
-
-export function insert_dev$legacy(target: Node, node: Node, anchor?: Node) {
-	dispatch_dev$legacy('SvelteDOMInsert', { target, node, anchor });
-	insert(target, node, anchor);
-}
-
-export function detach_dev$legacy(node: Node) {
-	dispatch_dev$legacy('SvelteDOMRemove', { node });
-	detach(node);
-}
-
-export function detach_between_dev$legacy(before: Node, after: Node) {
-	while (before.nextSibling && before.nextSibling !== after) {
-		detach_dev$legacy(before.nextSibling);
-	}
-}
-
-export function detach_before_dev$legacy(after: Node) {
-	while (after.previousSibling) {
-		detach_dev$legacy(after.previousSibling);
-	}
-}
-
-export function detach_after_dev$legacy(before: Node) {
-	while (before.nextSibling) {
-		detach_dev$legacy(before.nextSibling);
-	}
-}
-
-export function listen_dev$legacy(
-	node: Node,
-	event: string,
-	handler: EventListenerOrEventListenerObject,
-	options?: boolean | AddEventListenerOptions | EventListenerOptions,
-	has_prevent_default?: boolean,
-	has_stop_propagation?: boolean
-) {
-	const modifiers = options === true ? ['capture'] : options ? Array.from(Object.keys(options)) : [];
-	if (has_prevent_default) modifiers.push('preventDefault');
-	if (has_stop_propagation) modifiers.push('stopPropagation');
-
-	dispatch_dev$legacy('SvelteDOMAddEventListener', { node, event, handler, modifiers });
-
-	const dispose = listen(node, event, handler, options);
-	return () => {
-		dispatch_dev$legacy('SvelteDOMRemoveEventListener', { node, event, handler, modifiers });
-		dispose();
-	};
-}
-
-export function attr_dev$legacy(node: Element, attribute: string, value?: string) {
-	attr(node, attribute, value);
-
-	if (value == null) dispatch_dev$legacy('SvelteDOMRemoveAttribute', { node, attribute });
-	else dispatch_dev$legacy('SvelteDOMSetAttribute', { node, attribute, value });
-}
-
-export function prop_dev$legacy(node: Element, property: string, value?: any) {
-	node[property] = value;
-
-	dispatch_dev$legacy('SvelteDOMSetProperty', { node, property, value });
-}
-
-export function dataset_dev$legacy(node: HTMLElement, property: string, value?: any) {
-	node.dataset[property] = value;
-
-	dispatch_dev$legacy('SvelteDOMSetDataset', { node, property, value });
-}
-
-export function set_data_dev$legacy(text, data) {
-	data = '' + data;
-	if (text.data === data) return;
-
-	dispatch_dev$legacy('SvelteDOMSetData', { node: text, data });
-	text.data = data;
-}
-export function loop_guard_dev$legacy(timeout) {
-	const start = now();
-	return () => {
-		if (now() - start > timeout) {
-			throw new Error(`Infinite loop detected`);
-		}
-	};
-}
-export function validate_store_dev$legacy(store, name) {
-	if (store != null && typeof store.subscribe !== 'function') {
-		throw new Error(`'${name}' is not a store with a 'subscribe' method`);
-	}
-}
diff --git a/src/runtime/internal/dev.tools.ts b/src/runtime/internal/dev.tools.ts
deleted file mode 100644
index 58d6da9e49..0000000000
--- a/src/runtime/internal/dev.tools.ts
+++ /dev/null
@@ -1,147 +0,0 @@
-import { SvelteComponent } from './Component';
-
-const dev$context = {
-	block: null,
-	component: null,
-};
-abstract class Dev$ {
-	self;
-	parent_block = dev$context.block;
-	parent_component = dev$context.component;
-	constructor(self) {
-		this.self = self;
-	}
-	abstract add(type, payload): void;
-	abstract subscribers: {}[];
-	dispatch(type, payload: any) {
-		this.add(type, payload);
-		this.subscribers.forEach((subscriber) => {
-			if (type in subscriber) subscriber[type](payload);
-		});
-	}
-	subscribe(subscriber) {
-		this.subscribers.push(subscriber);
-		return () => {
-			const index = this.subscribers.indexOf(subscriber);
-			if (~index) this.subscribers.splice(index, 1);
-		};
-	}
-}
-class Dev$Component extends Dev$ {
-	self: SvelteComponent;
-	block;
-	add(type, payload) {}
-}
-class Dev$Block extends Dev$ {
-	self;
-	parent_block;
-	parent_component;
-	elements: Dev$Element[] = [];
-}
-class Dev$Element extends Dev$ {
-	component;
-	node;
-	parent;
-	children = [];
-	attributes: {};
-	eventListeners: {};
-	style: {};
-	class: {};
-	add(type, payload) {}
-	subscribers: Dev$ElementSubscriber[] = [];
-	dispatch(type, payload: any) {
-		this.add(type, payload);
-		this.subscribers.forEach((subscriber) => {
-			if (type in subscriber) subscriber[type](payload);
-		});
-	}
-	subscribe(subscriber) {
-		this.subscribers.push(subscriber);
-		return () => {
-			const index = this.subscribers.indexOf(subscriber);
-			if (~index) this.subscribers.splice(index, 1);
-		};
-	}
-}
-interface Dev$ElementSubscriber {
-	onMount(payload): void;
-	onUnmount(payload): void;
-	setAttribute(payload): void;
-	removeAttribute(payload): void;
-	addEventListener(payload): void;
-	removeEventListener(payload): void;
-	addClass(payload): void;
-	removeClass(payload): void;
-	addStyle(payload): void;
-	removeStyle(payload): void;
-}
-
-const dev$dispatch =
-	__DEV__ &&
-	!__TEST__ &&
-	typeof window !== 'undefined' &&
-	(function dev$create_hook() {
-		const subscribers = [];
-		const rootComponents = [];
-		const hook = {
-			version: __VERSION__,
-			has_subscribers: false,
-			subscribe(listener) {
-				this.has_subscribers = true;
-				subscribers.push(listener);
-				if (rootComponents.length) rootComponents.forEach((component) => listener.addRootComponent(component));
-				else listener.ping(`init-no-components`);
-				return () => {
-					const index = subscribers.indexOf(listener);
-					if (~index) {
-						subscribers.splice(index, 1);
-						this.has_subscribers = !!subscribers.length;
-						return true;
-					}
-					return false;
-				};
-			},
-		};
-		Object.defineProperty(window, `__SVELTE_DEVTOOLS_GLOBAL_HOOK__`, {
-			enumerable: false,
-			get() {
-				return hook;
-			},
-		});
-		return function update(target_type, event_type, ...values) {
-			if (!hook.has_subscribers) return;
-			subscribers.forEach((listener) => {
-				if (target_type in listener && event_type in listener[target_type]) {
-					listener[target_type][event_type](...values);
-				}
-			});
-		};
-	})();
-
-export function dev$element(element: Element | Node | EventTarget, event: keyof ElementEventsMap, payload?: any) {
-	if (__DEV__) {
-		dev$dispatch(`element`, event, element, payload);
-	}
-}
-export function dev$block(event: keyof BlockEventsMap, payload) {}
-export function dev$assert(truthy: any, else_throw: string) {
-	if (__DEV__ && !truthy) {
-		throw new Error(else_throw);
-	}
-}
-
-interface ElementEventsMap {
-	onMount;
-	onDestroy;
-	setAttribute;
-	removeAttribute;
-	addEventListener;
-	removeEventListener;
-	addClass;
-	removeClass;
-}
-interface BlockEventsMap {
-	'create';
-	'claim';
-	'claim.failed';
-}
diff --git a/src/runtime/internal/dev.ts b/src/runtime/internal/dev.ts
new file mode 100644
index 0000000000..b03672a762
--- /dev/null
+++ b/src/runtime/internal/dev.ts
@@ -0,0 +1,158 @@
+import { custom_event, append, insert, detach, listen, attr } from './dom';
+import { now, has_Symbol } from 'svelte/environment';
+import { SvelteComponent } from './Component';
+
+export function add_location_dev(element, file, line, column, char) {
+	element.__svelte_meta = {
+		loc: { file, line, column, char },
+	};
+}
+export function dispatch_dev<T = any>(type: string, detail?: T) {
+	document.dispatchEvent(custom_event(type, { version: __VERSION__, ...detail }));
+}
+
+export function append_dev(target: Node, node: Node) {
+	dispatch_dev('SvelteDOMInsert', { target, node });
+	append(target, node);
+}
+
+export function insert_dev(target: Node, node: Node, anchor?: Node) {
+	dispatch_dev('SvelteDOMInsert', { target, node, anchor });
+	insert(target, node, anchor);
+}
+
+export function detach_dev(node: Node) {
+	dispatch_dev('SvelteDOMRemove', { node });
+	detach(node);
+}
+
+export function detach_between_dev(before: Node, after: Node) {
+	while (before.nextSibling && before.nextSibling !== after) {
+		detach_dev(before.nextSibling);
+	}
+}
+
+export function detach_before_dev(after: Node) {
+	while (after.previousSibling) {
+		detach_dev(after.previousSibling);
+	}
+}
+
+export function detach_after_dev(before: Node) {
+	while (before.nextSibling) {
+		detach_dev(before.nextSibling);
+	}
+}
+
+export function listen_dev(
+	node: Node,
+	event: string,
+	handler: EventListenerOrEventListenerObject,
+	options?: boolean | AddEventListenerOptions | EventListenerOptions,
+	has_prevent_default?: boolean,
+	has_stop_propagation?: boolean
+) {
+	const modifiers = options === true ? ['capture'] : options ? Array.from(Object.keys(options)) : [];
+	if (has_prevent_default) modifiers.push('preventDefault');
+	if (has_stop_propagation) modifiers.push('stopPropagation');
+
+	dispatch_dev('SvelteDOMAddEventListener', { node, event, handler, modifiers });
+
+	const dispose = listen(node, event, handler, options);
+	return () => {
+		dispatch_dev('SvelteDOMRemoveEventListener', { node, event, handler, modifiers });
+		dispose();
+	};
+}
+
+export function attr_dev(node: Element, attribute: string, value?: string) {
+	attr(node, attribute, value);
+
+	if (value == null) dispatch_dev('SvelteDOMRemoveAttribute', { node, attribute });
+	else dispatch_dev('SvelteDOMSetAttribute', { node, attribute, value });
+}
+
+export function prop_dev(node: Element, property: string, value?: any) {
+	node[property] = value;
+
+	dispatch_dev('SvelteDOMSetProperty', { node, property, value });
+}
+
+export function dataset_dev(node: HTMLElement, property: string, value?: any) {
+	node.dataset[property] = value;
+
+	dispatch_dev('SvelteDOMSetDataset', { node, property, value });
+}
+
+export function set_data_dev(text, data) {
+	data = '' + data;
+	if (text.data === data) return;
+
+	dispatch_dev('SvelteDOMSetData', { node: text, data });
+	text.data = data;
+}
+export function loop_guard_dev(timeout) {
+	const start = now();
+	return () => {
+		if (now() - start > timeout) {
+			throw new Error(`Infinite loop detected`);
+		}
+	};
+}
+export function validate_store_dev(store, name) {
+	if (store != null && typeof store.subscribe !== 'function') {
+		throw new Error(
+			`Could not subscribe to $${name}. A valid store is an object with a .subscribe method, consider setting ${name} to null if this is expected.`
+		);
+	}
+}
+export const is_array_like_dev = (arg) => {
+	if (typeof arg !== 'string' && typeof arg === 'object' && !('length' in arg))
+		throw new Error(
+			`{#each} only iterates over Array-like Objects.${
+				has_Symbol && Symbol.iterator in arg
+					? ' Consider using a [...spread] to convert this iterable into an Array instead.'
+					: ''
+			}`
+		);
+};
+export const check_duplicate_keys_dev = (ctx, list, get_context, get_key) => {
+	const keys = new Set();
+	for (let i = 0; i < list.length; i++) {
+		const key = get_key(get_context(ctx, list, i));
+		if (keys.has(key)) {
+			throw new Error(`Cannot have duplicate keys in a keyed each`);
+		}
+		keys.add(key);
+	}
+};
+
+type Props = Record<string, any>;
+export interface SvelteComponentDev {
+	$set(props?: Props): void;
+	$on<T = any>(event: string, callback: (event: CustomEvent<T>) => void): () => void;
+	$destroy(): void;
+	[accessor: string]: any;
+}
+
+export class SvelteComponentDev extends SvelteComponent {
+	constructor(options: {
+		target: Element;
+		anchor?: Element;
+		props?: Props;
+		hydrate?: boolean;
+		intro?: boolean;
+		$$inline?: boolean;
+	}) {
+		if (!options || (!options.target && !options.$$inline)) throw new Error(`'target' is a required option`);
+		super();
+	}
+	$destroy() {
+		super.$destroy();
+		this.$destroy = () => {
+			console.warn(`Component was already destroyed`); // eslint-disable-line no-console
+		};
+	}
+	$capture_state() {}
+	$inject_state() {}
+}
diff --git a/src/runtime/internal/dev.utils.ts b/src/runtime/internal/dev.utils.ts
deleted file mode 100644
index aef0d3749e..0000000000
--- a/src/runtime/internal/dev.utils.ts
+++ /dev/null
@@ -1,56 +0,0 @@
-import { SvelteComponent } from './Component';
-import { now, has_Symbol } from 'svelte/environment';
-import { dev$assert } from './dev.tools';
-
-export const dev$is_array_like = (arg) =>
-	dev$assert(
-		typeof arg === 'string' || (typeof arg === 'object' && 'length' in arg),
-		`{#each} only iterates over Array-like Objects.${
-			has_Symbol && Symbol.iterator in arg
-				? ' Consider using a [...spread] to convert this iterable into an Array instead.'
-				: ''
-		}`
-	);
-
-export const dev$known_slots = (name, slot, keys) =>
-	Object.keys(slot).forEach((key) => dev$assert(keys.includes(key), `<${name}> received an unexpected slot "${key}".`));
-
-export const dev$is_valid_store = (store, name) =>
-	dev$assert(
-		typeof store === 'object' && (store === null || typeof store.subscribe === 'function'),
-		`Could not subscribe to $${name}. A valid store is an object with a .subscribe method, consider setting ${name} to null if this is expected.`
-	);
-
-export function dev$loop_guard(loopGuardTimeout) {
-	const start = now();
-	return () => dev$assert(now() - start < loopGuardTimeout, `Infinite loop detected`);
-}
-type Props = Record<string, any>;
-export interface SvelteComponentDev {
-	$set(props?: Props): void;
-	$on<T = any>(event: string, callback: (event: CustomEvent<T>) => void): () => void;
-	$destroy(): void;
-	[accessor: string]: any;
-}
-
-export class SvelteComponentDev extends SvelteComponent {
-	constructor(options: {
-		target: Element;
-		anchor?: Element;
-		props?: Props;
-		hydrate?: boolean;
-		intro?: boolean;
-		$$inline?: boolean;
-	}) {
-		if (!options || (!options.target && !options.$$inline)) throw new Error(`'target' is a required option`);
-		super();
-	}
-	$destroy() {
-		super.$destroy();
-		this.$destroy = () => {
-			console.warn(`Component was already destroyed`); // eslint-disable-line no-console
-		};
-	}
-	$capture_state() {}
-	$inject_state() {}
-}
diff --git a/src/runtime/internal/dom.ts b/src/runtime/internal/dom.ts
index 37512eb37a..42a352c0b6 100644
--- a/src/runtime/internal/dom.ts
+++ b/src/runtime/internal/dom.ts
@@ -1,18 +1,14 @@
-import { dev$element, dev$block } from './dev.tools';
 import { is_cors } from 'svelte/environment';
 
 export function append(target: Node, node: Node) {
-	dev$element(node, `onMount`, { target });
 	target.appendChild(node);
 }
 
 export function insert(target: Node, node: Node, anchor?: Node) {
-	dev$element(node, `onMount`, { target, anchor });
 	target.insertBefore(node, anchor || null);
 }
 
 export function detach(node: Node) {
-	dev$element(node, `onDestroy`);
 	node.parentNode.removeChild(node);
 }
 
@@ -21,14 +17,11 @@ export function destroy_each(iterations, detaching) {
 		if (iterations[i]) iterations[i].d(detaching);
 	}
 }
-const dev$create = <K>(elem: K) => (dev$block(`create`, elem), elem);
 export function element<K extends keyof HTMLElementTagNameMap>(name: K) {
-	if (__DEV__) return dev$create(document.createElement<K>(name));
 	return document.createElement<K>(name);
 }
 
 export function element_is<K extends keyof HTMLElementTagNameMap>(name: K, is: string) {
-	if (__DEV__) return dev$create(document.createElement<K>(name));
 	return document.createElement<K>(name, { is });
 }
 export function object_without_properties<T, K extends string[]>(obj: T, excluded: K) {
@@ -39,12 +32,10 @@ export function object_without_properties<T, K extends string[]>(obj: T, exclude
 }
 
 export function svg_element<K extends keyof SVGElementTagNameMap>(name: K): SVGElement {
-	if (__DEV__) return dev$create(document.createElementNS<K>('http://www.w3.org/2000/svg', name));
 	return document.createElementNS<K>('http://www.w3.org/2000/svg', name);
 }
 
 export function text(data: string) {
-	if (__DEV__) return dev$create(document.createTextNode(data));
 	return document.createTextNode(data);
 }
 
@@ -61,15 +52,6 @@ export function listen(
 	handler: EventListenerOrEventListenerObject,
 	options?: boolean | AddEventListenerOptions | EventListenerOptions
 ) {
-	if (__DEV__) {
-		const reference = { event, handler };
-		dev$element(node, `addEventListener`, reference);
-		node.addEventListener(event, handler, options);
-		return () => {
-			dev$element(node, `removeEventListener`, reference);
-			node.removeEventListener(event, handler, options);
-		};
-	}
 	node.addEventListener(event, handler, options);
 	return () => node.removeEventListener(event, handler, options);
 }
@@ -99,10 +81,8 @@ export function self(fn) {
 
 export function attr(node: Element, name: string, value?: any) {
 	if (value == null) {
-		dev$element(node, `removeAttribute`, { name });
 		node.removeAttribute(name);
 	} else if (node.getAttribute(name) !== value) {
-		dev$element(node, `setAttribute`, { name, value });
 		node.setAttribute(name, value);
 	}
 }
@@ -113,13 +93,10 @@ export function set_attributes(node: HTMLElement, attributes: { [x: string]: any
 	let name;
 	for (name in attributes) {
 		if (attributes[name] == null) {
-			dev$element(node, `removeAttribute`, { name });
 			node.removeAttribute(name);
 		} else if (name === 'style') {
-			dev$element(node, `setAttribute`, { name, value: attributes[name] });
 			node.style.cssText = attributes[name];
 		} else if (name === '__value' || (descriptors[name] && descriptors[name].set)) {
-			dev$element(node, `setAttribute`, { name, value: attributes[name] });
 			node[name] = attributes[name];
 		} else {
 			attr(node, name, attributes[name]);
@@ -136,7 +113,6 @@ export function set_svg_attributes(node: SVGElement, attributes: { [x: string]:
 
 export function set_custom_element_data(node, name, value) {
 	if (name in node) {
-		dev$element(node, `setAttribute`, { name, value });
 		node[name] = value;
 	} else {
 		attr(node, name, value);
@@ -144,7 +120,6 @@ export function set_custom_element_data(node, name, value) {
 }
 
 export function xlink_attr(node: Element, name, value) {
-	dev$element(node, `setAttribute`, { name, value });
 	node.setAttributeNS('http://www.w3.org/1999/xlink', name, value);
 }
 
@@ -178,20 +153,16 @@ export function claim_element(nodes, name, attributes, is_svg) {
 				if (attributes[(a = n.attributes[j]).name]) j++;
 				else n.removeAttribute(a.name);
 			}
-			dev$block(`claim`, n);
 			return nodes.splice(i, 1)[0];
 		}
-	dev$block(`claim.failed`, name);
 	return is_svg ? svg_element(name) : element(name);
 }
 
 export function claim_text(nodes, data) {
 	for (let i = 0, n; i < nodes.length; i += 1)
 		if ((n = nodes[i]).nodeType === 3) {
-			dev$block(`claim`, n);
 			return (n.data = '' + data), nodes.splice(i, 1)[0];
 		}
-	dev$block(`claim.failed`, 'text');
 	return text(data);
 }
 
@@ -202,33 +173,28 @@ export function claim_space(nodes) {
 export function set_data(text, data) {
 	if (text.data !== (data = '' + data)) {
 		text.data = data;
-		dev$element(text, `setAttribute`, { name: 'data', value: data });
 	}
 }
 
 export function set_input_value(input, value) {
 	if (value != null || input.value) {
 		input.value = value;
-		dev$element(input, `setAttribute`, { name: 'value', value });
 	}
 }
 
 export function set_input_type(input, type) {
 	try {
 		input.type = type;
-		dev$element(input, `setAttribute`, { name: 'type', value: type });
 	} catch (e) {}
 }
 
 export function set_style(node, property, value, is_important?) {
-	dev$element(node, `setAttribute`, { name: 'style', property, value });
 	node.style.setProperty(property, value, is_important ? 'important' : '');
 }
 
 export function select_option(select, value) {
 	for (let i = 0, o; i < select.options.length; i += 1) {
 		if ((o = select.options[i]).__value === value) {
-			dev$element(o, `setAttribute`, { name: 'selected', value: true });
 			o.selected = true;
 			return;
 		}
@@ -237,13 +203,6 @@ export function select_option(select, value) {
 
 export function select_options(select, value) {
 	for (let i = 0, o; i < select.options.length; i += 1) {
-		if (__DEV__) {
-			dev$element((o = select.options[i]), `setAttribute`, {
-				name: 'selected',
-				value: (o = select.options[i]).selected = ~value.indexOf(o.__value),
-			});
-			continue;
-		}
 		(o = select.options[i]).selected = ~value.indexOf(o.__value);
 	}
 }
@@ -297,7 +256,6 @@ export function add_resize_listener(node: HTMLElement, fn: () => void) {
 }
 
 export function toggle_class(element, name, toggle) {
-	dev$element(element, toggle ? 'addClass' : 'removeClass', { name });
 	element.classList[toggle ? 'add' : 'remove'](name);
 }
 
diff --git a/src/runtime/internal/index.ts b/src/runtime/internal/index.ts
index b154e4cd3d..1708bf3f80 100644
--- a/src/runtime/internal/index.ts
+++ b/src/runtime/internal/index.ts
@@ -1,9 +1,7 @@
 export * from './animations';
 export * from './await_block';
 export * from './Component';
-export * from './dev.legacy';
-export * from './dev.utils';
-export * from './dev.tools';
+export * from './dev';
 export * from './dom';
 export * from './keyed_each';
 export * from './lifecycle';
@@ -16,5 +14,5 @@ export * from './stores';
 export * from './transitions';
 export * from './utils';
 
-// todo; create_module.ts line 24; allow compiler to import non internal
+// todo: [create_module.ts line 24] allow compiler to import non internal
 export * from '../environment/index';
diff --git a/src/runtime/internal/keyed_each.ts b/src/runtime/internal/keyed_each.ts
index 4fa0c6b515..3c89c01e4b 100644
--- a/src/runtime/internal/keyed_each.ts
+++ b/src/runtime/internal/keyed_each.ts
@@ -95,14 +95,3 @@ export const update_keyed_each = (
 
 	return new_blocks;
 };
-
-export function validate_each_keys(ctx, list, get_context, get_key) {
-	const keys = new Set();
-	for (let i = 0; i < list.length; i++) {
-		const key = get_key(get_context(ctx, list, i));
-		if (keys.has(key)) {
-			throw new Error(`Cannot have duplicate keys in a keyed each`);
-		}
-		keys.add(key);
-	}
-}
diff --git a/src/runtime/internal/lifecycle.ts b/src/runtime/internal/lifecycle.ts
index 7c400bef6b..591eea5119 100644
--- a/src/runtime/internal/lifecycle.ts
+++ b/src/runtime/internal/lifecycle.ts
@@ -1,41 +1,42 @@
 import { custom_event } from './dom';
-import { SvelteComponentDev } from './dev.utils';
 import { SvelteComponent } from './Component';
-import { dev$assert } from './dev.tools';
-
+import { SvelteComponentDev } from './dev';
 export let current_component: SvelteComponentDev | SvelteComponent | null;
 
 export const set_current_component = (component) => (current_component = component);
 
-const dev$on_init_only = (name: string) =>
-	dev$assert(!!current_component, `${name} cannot be called outside of component initialization`);
+const on_init_only = (name: string) => {
+	if (!current_component) {
+		throw new Error(`${name} cannot be called outside of component initialization`);
+	}
+};
 
 export function get_current_component() {
 	return current_component;
 }
 
 export function beforeUpdate(fn) {
-	dev$on_init_only(`beforeUpdate`);
+	on_init_only(`beforeUpdate`);
 	return current_component.$$.before_update.push(fn);
 }
 
 export function onMount(fn) {
-	dev$on_init_only(`onMount`);
+	on_init_only(`onMount`);
 	return current_component.$$.on_mount.push(fn);
 }
 
 export function afterUpdate(fn) {
-	dev$on_init_only(`afterUpdate`);
+	on_init_only(`afterUpdate`);
 	return current_component.$$.after_update.push(fn);
 }
 
 export function onDestroy(fn) {
-	dev$on_init_only(`onDestroy`);
+	on_init_only(`onDestroy`);
 	return current_component.$$.on_destroy.push(fn);
 }
 // todo : deprecate
 export function createEventDispatcher() {
-	dev$on_init_only(`createEventDispatcher`);
+	on_init_only(`createEventDispatcher`);
 	const component = current_component;
 	return (type: string, detail?: any) => {
 		const callbacks = component.$$.callbacks[type];
@@ -50,12 +51,12 @@ export function createEventDispatcher() {
 }
 
 export function setContext(key, context) {
-	dev$on_init_only(`setContext`);
+	on_init_only(`setContext`);
 	current_component.$$.context.set(key, context);
 }
 
 export function getContext(key) {
-	dev$on_init_only(`getContext`);
+	on_init_only(`getContext`);
 	return current_component.$$.context.get(key);
 }
 
diff --git a/src/runtime/internal/scheduler.ts b/src/runtime/internal/scheduler.ts
index 5be0e527b7..5bf98aa8c8 100644
--- a/src/runtime/internal/scheduler.ts
+++ b/src/runtime/internal/scheduler.ts
@@ -13,8 +13,8 @@ const measure_callbacks = [];
 const flush_callbacks = [];
 
 // todo : remove add_flush_callback
-export const add_flush_callback = Array.prototype.push.bind(flush_callbacks);
-export const add_measure_callback = Array.prototype.push.bind(measure_callbacks);
+export const add_flush_callback = /*#__PURE__*/ Array.prototype.push.bind(flush_callbacks);
+export const add_measure_callback = /*#__PURE__*/ Array.prototype.push.bind(measure_callbacks);
 
 const seen_render_callbacks = new Set();
 export const add_render_callback = (fn) => {
diff --git a/src/runtime/internal/style_manager.ts b/src/runtime/internal/style_manager.ts
index 14affaa408..7ab324b94e 100644
--- a/src/runtime/internal/style_manager.ts
+++ b/src/runtime/internal/style_manager.ts
@@ -7,7 +7,7 @@ const document_uid = new Map();
 const document_stylesheets = new Map();
 
 const current_rules = new Set();
-export const animate_css = Function.prototype.call.bind(function animate_css(
+export const animate_css = /*#__PURE__*/ Function.prototype.call.bind(function animate_css(
 	this: HTMLElement,
 	css: (t: number) => string,
 	duration: number,
diff --git a/src/runtime/internal/transitions.ts b/src/runtime/internal/transitions.ts
index 64104ecf70..4098b723bc 100644
--- a/src/runtime/internal/transitions.ts
+++ b/src/runtime/internal/transitions.ts
@@ -48,7 +48,6 @@ export const group_transition_out = (fn) => {
 	transition_group = transition_group.p;
 };
 
-/* todo: deprecate */
 const swap = (fn, rx) =>
 	fn.length === 1 ? (rx & tx.intro ? fn : (t) => fn(1 - t)) : rx & tx.intro ? (t) => fn(t, 1 - t) : (t) => fn(1 - t, t);
 
@@ -69,7 +68,7 @@ export enum tx {
 	bidirectional_outro = 6,
 	animation = 8,
 }
-export const run_transition = Function.prototype.call.bind(function transition(
+export const run_transition = /*#__PURE__*/ Function.prototype.call.bind(function transition(
 	this: HTMLElement,
 	fn: TransitionFn,
 	rx: tx,
@@ -94,7 +93,7 @@ export const run_transition = Function.prototype.call.bind(function transition(
 	add_measure_callback(() => {
 		if (null === (config = fn(this, params))) return noop;
 		return (t) => {
-			if (false === running) return void (running = false);
+			if (false === running) return;
 			if ('then' in config) return void config.then(stop);
 
 			let { delay = 0, duration = 300, easing, tick, css, strategy = 'reverse' }: TransitionConfig =
@@ -160,7 +159,7 @@ export const run_transition = Function.prototype.call.bind(function transition(
 });
 
 const running_bidi: Map<HTMLElement, StopResetReverse> = new Map();
-export const run_bidirectional_transition = Function.prototype.call.bind(function bidirectional(
+export const run_bidirectional_transition = /*#__PURE__*/ Function.prototype.call.bind(function bidirectional(
 	this: HTMLElement,
 	fn: TransitionFn,
 	rx: tx.intro | tx.outro,
diff --git a/src/runtime/motion/index.ts b/src/runtime/motion/index.ts
index 57267c4a63..3bea3d8c0a 100644
--- a/src/runtime/motion/index.ts
+++ b/src/runtime/motion/index.ts
@@ -73,7 +73,7 @@ export function spring(
 	};
 	return obj;
 }
-export function tween<T>(
+export function tweened<T>(
 	value: T,
 	{
 		delay: default_delay = 0,