diff --git a/.changeset/sour-cherries-play.md b/.changeset/sour-cherries-play.md
new file mode 100644
index 000000000000..17baa59e14a5
--- /dev/null
+++ b/.changeset/sour-cherries-play.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Tighten up params typings, fix load function typings, add event typings to generated types
diff --git a/packages/kit/src/core/sync/write_types.js b/packages/kit/src/core/sync/write_types.js
index 0eb629f45e70..34ec6f33e7bf 100644
--- a/packages/kit/src/core/sync/write_types.js
+++ b/packages/kit/src/core/sync/write_types.js
@@ -246,12 +246,18 @@ function write_types_for_dir(config, manifest_data, routes_dir, dir, groups, ts)
 
 		exports.push(`export type PageData = ${data};`);
 		if (load) {
-			exports.push(`export type PageLoad = ${load};`);
+			exports.push(
+				`export type PageLoad<OutputData extends Record<string, any> | void = Record<string, any> | void> = ${load};`
+			);
+			exports.push('export type PageLoadEvent = Parameters<PageLoad>[0];');
 		}
 
 		exports.push(`export type PageServerData = ${server_data};`);
 		if (server_load) {
-			exports.push(`export type PageServerLoad = ${server_load};`);
+			exports.push(
+				`export type PageServerLoad<OutputData extends Record<string, any> | void = Record<string, any> | void> = ${server_load};`
+			);
+			exports.push('export type PageServerLoadEvent = Parameters<PageServerLoad>[0];');
 		}
 
 		if (group.leaf.server) {
@@ -292,12 +298,18 @@ function write_types_for_dir(config, manifest_data, routes_dir, dir, groups, ts)
 
 			exports.push(`export type LayoutData = ${data};`);
 			if (load) {
-				exports.push(`export type LayoutLoad = ${load};`);
+				exports.push(
+					`export type LayoutLoad<OutputData extends Record<string, any> | void = Record<string, any> | void> = ${load};`
+				);
+				exports.push('export type LayoutLoadEvent = Parameters<LayoutLoad>[0];');
 			}
 
 			exports.push(`export type LayoutServerData = ${server_data};`);
 			if (server_load) {
-				exports.push(`export type LayoutServerLoad = ${server_load};`);
+				exports.push(
+					`export type LayoutServerLoad<OutputData extends Record<string, any> | void = Record<string, any> | void> = ${server_load};`
+				);
+				exports.push('export type LayoutServerLoadEvent = Parameters<LayoutServerLoad>[0];');
 			}
 		}
 
@@ -311,9 +323,15 @@ function write_types_for_dir(config, manifest_data, routes_dir, dir, groups, ts)
 			/** @type {string[]} */
 			const load_exports = [];
 
+			/** @type {string[]} */
+			const load_event_exports = [];
+
 			/** @type {string[]} */
 			const server_load_exports = [];
 
+			/** @type {string[]} */
+			const server_load_event_exports = [];
+
 			for (const [name, node] of group.named_layouts) {
 				const { data, server_data, load, server_load, written_proxies } = process_node(
 					ts,
@@ -326,26 +344,39 @@ function write_types_for_dir(config, manifest_data, routes_dir, dir, groups, ts)
 				data_exports.push(`export type ${name} = ${data};`);
 				server_data_exports.push(`export type ${name} = ${server_data};`);
 				if (load) {
-					load_exports.push(`export type ${name} = ${load};`);
+					load_exports.push(
+						`export type ${name}<OutputData extends Record<string, any> | void = Record<string, any> | void> = ${load};`
+					);
+					load_event_exports.push(`export type ${name} = Parameters<LayoutLoad.${name}>[0];`);
 				}
 				if (server_load) {
-					server_load_exports.push(`export type ${name} = ${load};`);
+					server_load_exports.push(
+						`export type ${name}<OutputData extends Record<string, any> | void = Record<string, any> | void> = ${load};`
+					);
+					server_load_event_exports.push(
+						`export type ${name} = Parameters<LayoutServerLoad.${name}>[0];`
+					);
 				}
 			}
 
 			exports.push(`\nexport namespace LayoutData {\n\t${data_exports.join('\n\t')}\n}`);
 			exports.push(`\nexport namespace LayoutLoad {\n\t${load_exports.join('\n\t')}\n}`);
+			exports.push(`\nexport namespace LayoutLoadEvent {\n\t${load_event_exports.join('\n\t')}\n}`);
 			exports.push(
 				`\nexport namespace LayoutServerData {\n\t${server_data_exports.join('\n\t')}\n}`
 			);
 			exports.push(
 				`\nexport namespace LayoutServerLoad {\n\t${server_load_exports.join('\n\t')}\n}`
 			);
+			exports.push(
+				`\nexport namespace LayoutServerLoadEvent {\n\t${server_load_event_exports.join('\n\t')}\n}`
+			);
 		}
 	}
 
 	if (group.endpoint) {
 		exports.push(`export type RequestHandler = Kit.RequestHandler<RouteParams>;`);
+		exports.push(`export type RequestEvent = Kit.RequestEvent<RouteParams>;`);
 	}
 
 	const output = [imports.join('\n'), declarations.join('\n'), exports.join('\n')]
@@ -384,7 +415,7 @@ function process_node(ts, node, outdir, params, groups) {
 		}
 
 		server_data = get_data_type(node.server, 'load', 'null', proxy);
-		server_load = `Kit.ServerLoad<${params}, ${get_parent_type('LayoutServerData')}>`;
+		server_load = `Kit.ServerLoad<${params}, ${get_parent_type('LayoutServerData')}, OutputData>`;
 
 		if (proxy) {
 			const types = [];
@@ -415,7 +446,7 @@ function process_node(ts, node, outdir, params, groups) {
 		}
 
 		data = get_data_type(node.shared, 'load', server_data, proxy);
-		load = `Kit.Load<${params}, ${server_data}, ${get_parent_type('LayoutData')}>`;
+		load = `Kit.Load<${params}, ${server_data}, ${get_parent_type('LayoutData')}, OutputData>`;
 	} else {
 		data = server_data;
 	}
@@ -468,7 +499,7 @@ function process_node(ts, node, outdir, params, groups) {
 			parent = parent_layout.parent;
 		}
 
-		let parent_str = parent_imports[0] || 'null';
+		let parent_str = parent_imports[0] || 'Record<never, never>';
 		for (let i = 1; i < parent_imports.length; i++) {
 			// Omit is necessary because a parent could have a property with the same key which would
 			// cause a type conflict. At runtime the child overwrites the parent property in this case,
diff --git a/packages/kit/src/runtime/client/client.js b/packages/kit/src/runtime/client/client.js
index 4600be85a1d9..f500b14d3831 100644
--- a/packages/kit/src/runtime/client/client.js
+++ b/packages/kit/src/runtime/client/client.js
@@ -448,7 +448,7 @@ export function create_client({ target, base, trailing_slash }) {
 	 *   url: URL;
 	 *   params: Record<string, string>;
 	 *   routeId: string | null;
-	 * 	 server_data: import('types').JSONObject | null;
+	 * 	 server_data: Record<string, any> | null;
 	 * }} options
 	 * @returns {Promise<import('./types').BranchNode>}
 	 */
diff --git a/packages/kit/src/runtime/client/types.d.ts b/packages/kit/src/runtime/client/types.d.ts
index 493d2fb6e432..bfcbc3dd59c8 100644
--- a/packages/kit/src/runtime/client/types.d.ts
+++ b/packages/kit/src/runtime/client/types.d.ts
@@ -6,7 +6,7 @@ import {
 	prefetch,
 	prefetchRoutes
 } from '$app/navigation';
-import { CSRPageNode, CSRRoute, JSONObject } from 'types';
+import { CSRPageNode, CSRRoute } from 'types';
 import { HttpError } from '../../index/private.js';
 import { SerializedHttpError } from '../server/page/types.js';
 
@@ -92,7 +92,7 @@ export interface ServerDataRedirected {
 export interface ServerDataLoaded {
 	type: 'data';
 	nodes: Array<{
-		data?: JSONObject | null; // TODO or `-1` to indicate 'reuse cached data'?
+		data?: Record<string, any> | null; // TODO or `-1` to indicate 'reuse cached data'?
 		status?: number;
 		message?: string;
 		error?: {
diff --git a/packages/kit/src/runtime/server/endpoint.js b/packages/kit/src/runtime/server/endpoint.js
index ab6cbfc027e6..338791b4d0b1 100644
--- a/packages/kit/src/runtime/server/endpoint.js
+++ b/packages/kit/src/runtime/server/endpoint.js
@@ -29,7 +29,9 @@ export async function render_endpoint(event, route) {
 		return method_not_allowed(mod, method);
 	}
 
-	const response = await handler(event);
+	const response = await handler(
+		/** @type {import('types').RequestEvent<Record<string, any>>} */ (event)
+	);
 
 	if (!(response instanceof Response)) {
 		return new Response(
diff --git a/packages/kit/src/runtime/server/index.js b/packages/kit/src/runtime/server/index.js
index 3d7c8c2ebb3d..625fc053953b 100644
--- a/packages/kit/src/runtime/server/index.js
+++ b/packages/kit/src/runtime/server/index.js
@@ -257,7 +257,7 @@ export async function respond(request, options, state) {
 											event,
 											node,
 											parent: async () => {
-												/** @type {import('types').JSONObject} */
+												/** @type {Record<string, any>} */
 												const data = {};
 												for (let j = 0; j < i; j += 1) {
 													const parent = await promises[j];
diff --git a/packages/kit/src/runtime/server/page/index.js b/packages/kit/src/runtime/server/page/index.js
index c168cf56df71..9840a417c660 100644
--- a/packages/kit/src/runtime/server/page/index.js
+++ b/packages/kit/src/runtime/server/page/index.js
@@ -137,7 +137,7 @@ export async function render_page(event, route, options, state, resolve_opts) {
 		/** @type {Error | null} */
 		let load_error = null;
 
-		/** @type {Array<Promise<import('types').JSONObject | null>>} */
+		/** @type {Array<Promise<Record<string, any> | null>>} */
 		const server_promises = nodes.map((node, i) => {
 			if (load_error) {
 				// if an error happens immediately, don't bother with the rest of the nodes
@@ -156,7 +156,7 @@ export async function render_page(event, route, options, state, resolve_opts) {
 						event,
 						node,
 						parent: async () => {
-							/** @type {import('types').JSONObject} */
+							/** @type {Record<string, any>} */
 							const data = {};
 							for (let j = 0; j < i; j += 1) {
 								Object.assign(data, await server_promises[j]);
diff --git a/packages/kit/src/runtime/server/page/load_data.js b/packages/kit/src/runtime/server/page/load_data.js
index 04872ad72bb4..ef73137fc27e 100644
--- a/packages/kit/src/runtime/server/page/load_data.js
+++ b/packages/kit/src/runtime/server/page/load_data.js
@@ -5,7 +5,7 @@ import { LoadURL, PrerenderingURL } from '../../../utils/url.js';
  * @param {{
  *   event: import('types').RequestEvent;
  *   node: import('types').SSRNode | undefined;
- *   parent: () => Promise<import('types').JSONObject | null>;
+ *   parent: () => Promise<Record<string, any>>;
  * }} opts
  */
 export async function load_server_data({ event, node, parent }) {
@@ -37,7 +37,7 @@ export async function load_server_data({ event, node, parent }) {
  *   fetcher: typeof fetch;
  *   node: import('types').SSRNode | undefined;
  *   parent: () => Promise<Record<string, any>>;
- *   server_data_promise: Promise<import('types').JSONObject | null>;
+ *   server_data_promise: Promise<Record<string, any> | null>;
  *   state: import('types').SSRState;
  * }} opts
  */
@@ -70,7 +70,7 @@ export async function load_data({ event, fetcher, node, parent, server_data_prom
 
 /** @param {Record<string, any>} object */
 async function unwrap_promises(object) {
-	/** @type {import('types').JSONObject} */
+	/** @type {Record<string, any>} */
 	const unwrapped = {};
 
 	for (const key in object) {
diff --git a/packages/kit/src/runtime/server/page/render.js b/packages/kit/src/runtime/server/page/render.js
index 835b0b7b0986..31d9f494a8dd 100644
--- a/packages/kit/src/runtime/server/page/render.js
+++ b/packages/kit/src/runtime/server/page/render.js
@@ -86,7 +86,7 @@ export async function render_response({
 			/** @type {import('types').Page} */
 			page: {
 				error,
-				params: event.params,
+				params: /** @type {Record<string, any>} */ (event.params),
 				routeId: event.routeId,
 				status,
 				url: state.prerendering ? new PrerenderingURL(event.url) : event.url,
diff --git a/packages/kit/src/runtime/server/page/types.d.ts b/packages/kit/src/runtime/server/page/types.d.ts
index 556496ee3486..c3230ddf995a 100644
--- a/packages/kit/src/runtime/server/page/types.d.ts
+++ b/packages/kit/src/runtime/server/page/types.d.ts
@@ -1,4 +1,4 @@
-import { JSONValue, ResponseHeaders, SSRNode, CspDirectives } from 'types';
+import { ResponseHeaders, SSRNode, CspDirectives } from 'types';
 import { HttpError } from '../../../index/private';
 
 export interface Fetched {
@@ -21,7 +21,7 @@ export interface FetchState {
 export type Loaded = {
 	node: SSRNode;
 	data: Record<string, any> | null;
-	server_data: JSONValue;
+	server_data: any;
 };
 
 type CspMode = 'hash' | 'nonce' | 'auto';
diff --git a/packages/kit/src/utils/escape.js b/packages/kit/src/utils/escape.js
index 051cc9d053a7..959a160677c2 100644
--- a/packages/kit/src/utils/escape.js
+++ b/packages/kit/src/utils/escape.js
@@ -37,7 +37,7 @@ const render_json_payload_script_regex = new RegExp(
  * Attribute names must be type-checked so we don't need to escape them.
  *
  * @param {import('types').PayloadScriptAttributes} attrs A list of attributes to be added to the element.
- * @param {import('types').JSONValue} payload The data to be carried by the element. Must be serializable to JSON.
+ * @param {any} payload The data to be carried by the element. Must be serializable to JSON.
  * @returns {string} The raw HTML of a script element carrying the JSON payload.
  * @example const html = render_json_payload_script({ type: 'data', url: '/data.json' }, { foo: 'bar' });
  */
diff --git a/packages/kit/types/index.d.ts b/packages/kit/types/index.d.ts
index 8070cd969347..54ad5152d7ce 100644
--- a/packages/kit/types/index.d.ts
+++ b/packages/kit/types/index.d.ts
@@ -7,8 +7,6 @@ import { CompileOptions } from 'svelte/types/compiler/interfaces';
 import {
 	AdapterEntry,
 	CspDirectives,
-	JSONObject,
-	JSONValue,
 	Logger,
 	MaybePromise,
 	Prerendered,
@@ -194,18 +192,18 @@ export interface HandleError {
  * rather than using `Load` directly.
  */
 export interface Load<
-	Params extends Record<string, string> = Record<string, string>,
-	InputData extends JSONObject | null = JSONObject | null,
-	ParentData extends Record<string, any> | null = Record<string, any> | null,
-	OutputData extends Record<string, any> = Record<string, any>
+	Params extends Partial<Record<string, string>> = Partial<Record<string, string>>,
+	InputData extends Record<string, any> | null = Record<string, any> | null,
+	ParentData extends Record<string, any> = Record<string, any>,
+	OutputData extends Record<string, any> | void = Record<string, any> | void
 > {
-	(event: LoadEvent<Params, InputData, ParentData>): MaybePromise<OutputData | void>;
+	(event: LoadEvent<Params, InputData, ParentData>): MaybePromise<OutputData>;
 }
 
 export interface LoadEvent<
-	Params extends Record<string, string> = Record<string, string>,
-	Data extends JSONObject | null = JSONObject | null,
-	ParentData extends Record<string, any> | null = Record<string, any> | null
+	Params extends Partial<Record<string, string>> = Partial<Record<string, string>>,
+	Data extends Record<string, any> | null = Record<string, any> | null,
+	ParentData extends Record<string, any> = Record<string, any>
 > {
 	fetch(info: RequestInfo, init?: RequestInit): Promise<Response>;
 	params: Params;
@@ -235,7 +233,9 @@ export interface ParamMatcher {
 	(param: string): boolean;
 }
 
-export interface RequestEvent<Params extends Record<string, string> = Record<string, string>> {
+export interface RequestEvent<
+	Params extends Partial<Record<string, string>> = Partial<Record<string, string>>
+> {
 	clientAddress: string;
 	locals: App.Locals;
 	params: Params;
@@ -260,8 +260,6 @@ export interface ResolveOptions {
 	transformPageChunk?: (input: { html: string; done: boolean }) => MaybePromise<string | undefined>;
 }
 
-export type ResponseBody = JSONValue | Uint8Array | ReadableStream | Error;
-
 export class Server {
 	constructor(manifest: SSRManifest);
 	init(options: ServerInitOptions): void;
@@ -295,21 +293,23 @@ export interface SSRManifest {
  * rather than using `ServerLoad` directly.
  */
 export interface ServerLoad<
-	Params extends Record<string, string> = Record<string, string>,
-	ParentData extends JSONObject | null = JSONObject | null,
-	OutputData extends JSONObject | void = JSONObject | void
+	Params extends Partial<Record<string, string>> = Partial<Record<string, string>>,
+	ParentData extends Record<string, any> = Record<string, any>,
+	OutputData extends Record<string, any> | void = Record<string, any> | void
 > {
-	(event: ServerLoadEvent<Params, ParentData>): MaybePromise<OutputData | void>;
+	(event: ServerLoadEvent<Params, ParentData>): MaybePromise<OutputData>;
 }
 
 export interface ServerLoadEvent<
-	Params extends Record<string, string> = Record<string, string>,
-	ParentData extends JSONObject | null = JSONObject | null
+	Params extends Partial<Record<string, string>> = Partial<Record<string, string>>,
+	ParentData extends Record<string, any> = Record<string, any>
 > extends RequestEvent<Params> {
 	parent: () => Promise<ParentData>;
 }
 
-export interface Action<Params extends Record<string, string> = Record<string, string>> {
+export interface Action<
+	Params extends Partial<Record<string, string>> = Partial<Record<string, string>>
+> {
 	(event: RequestEvent<Params>): MaybePromise<
 		| { status?: number; errors: Record<string, string>; location?: never }
 		| { status?: never; errors?: never; location: string }
diff --git a/packages/kit/types/private.d.ts b/packages/kit/types/private.d.ts
index 7537f63efe25..f517091c29a5 100644
--- a/packages/kit/types/private.d.ts
+++ b/packages/kit/types/private.d.ts
@@ -26,15 +26,6 @@ export interface AdapterEntry {
 	}) => MaybePromise<void>;
 }
 
-// TODO is this still used?
-export type BodyValidator<T> = {
-	[P in keyof T]: T[P] extends { [k: string]: unknown }
-		? BodyValidator<T[P]> // recurse when T[P] is an object
-		: T[P] extends BigInt | Function | Symbol
-		? never
-		: T[P];
-};
-
 // Based on https://github.com/josh-hemphill/csp-typed-directives/blob/latest/src/csp.types.ts
 //
 // MIT License
@@ -145,20 +136,6 @@ export interface CspDirectives {
 
 export type HttpMethod = 'GET' | 'HEAD' | 'POST' | 'PUT' | 'DELETE' | 'PATCH';
 
-export interface JSONObject {
-	[key: string]: JSONValue;
-}
-
-export type JSONValue =
-	| string
-	| number
-	| boolean
-	| null
-	| undefined
-	| ToJSON
-	| JSONValue[]
-	| JSONObject;
-
 export interface Logger {
 	(msg: string): void;
 	success(msg: string): void;
@@ -229,8 +206,4 @@ export interface RouteSegment {
 	rest: boolean;
 }
 
-export interface ToJSON {
-	toJSON(...args: any[]): Exclude<JSONValue, ToJSON>;
-}
-
 export type TrailingSlash = 'never' | 'always' | 'ignore';