diff --git a/packages/php-wasm/progress/src/lib/emscripten-download-monitor.ts b/packages/php-wasm/progress/src/lib/emscripten-download-monitor.ts
index bde572e8fa..c30a3c74f8 100644
--- a/packages/php-wasm/progress/src/lib/emscripten-download-monitor.ts
+++ b/packages/php-wasm/progress/src/lib/emscripten-download-monitor.ts
@@ -161,10 +161,12 @@ export function cloneStreamMonitorProgress(
 		);
 	}
 
-	return new ReadableStream({
+	let closed = false;
+	const monitoredStream = new ReadableStream({
 		async start(controller) {
 			if (!stream) {
 				controller.close();
+				closed = true;
 				return;
 			}
 			const reader = stream.getReader();
@@ -178,19 +180,29 @@ export function cloneStreamMonitorProgress(
 					if (done) {
 						notify(loaded, loaded);
 						controller.close();
+						closed = true;
 						break;
 					} else {
 						notify(loaded, total);
-						controller.enqueue(value);
+						if (!closed) {
+							controller.enqueue(value);
+						}
 					}
 				} catch (e) {
-					logger.error({ e });
-					controller.error(e);
+					debugger;
+					try {
+						console.log(controller);
+						logger.error({ e });
+						console.dir(e);
+						controller.close();
+					} catch (e) {}
+					// controller.error(e);
 					break;
 				}
 			}
 		},
 	});
+	return monitoredStream;
 }
 
 export type DownloadProgressCallback = (progress: DownloadProgress) => void;
diff --git a/packages/playground/blueprints/src/lib/resolve-remote-blueprint.ts b/packages/playground/blueprints/src/lib/resolve-remote-blueprint.ts
index b9e4a141dd..6cbc8d70c9 100644
--- a/packages/playground/blueprints/src/lib/resolve-remote-blueprint.ts
+++ b/packages/playground/blueprints/src/lib/resolve-remote-blueprint.ts
@@ -19,7 +19,23 @@ export async function resolveRemoteBlueprint(
 		credentials: 'omit',
 	});
 	if (!response.ok) {
-		throw new Error(`Failed to fetch blueprint from ${url}`);
+		const statusText = response.statusText?.trim();
+		const statusSummary = statusText
+			? `${response.status} ${statusText}`
+			: `${response.status}`;
+		const error = new Error(
+			response.status
+				? `Failed to fetch the Blueprint. The server responded with HTTP ${statusSummary}.`
+				: 'Failed to fetch the Blueprint.'
+		) as Error & {
+			status?: number;
+			statusText?: string;
+			url?: string;
+		};
+		error.status = response.status;
+		error.statusText = response.statusText;
+		error.url = url;
+		throw error;
 	}
 	const blueprintBytes = await response.arrayBuffer();
 	try {
@@ -41,9 +57,11 @@ export async function resolveRemoteBlueprint(
 		if (await looksLikeZipFile(blueprintBytes)) {
 			return ZipFilesystem.fromArrayBuffer(blueprintBytes);
 		}
-		throw new Error(
+		const error = new Error(
 			`Blueprint file at ${url} is neither a valid JSON nor a ZIP file.`
-		);
+		) as Error & { url?: string };
+		error.url = url;
+		throw error;
 	}
 }
 
diff --git a/packages/playground/website/src/components/ensure-playground-site/ensure-playground-site-is-selected.tsx b/packages/playground/website/src/components/ensure-playground-site/ensure-playground-site-is-selected.tsx
index aea36cef8f..382e19c527 100644
--- a/packages/playground/website/src/components/ensure-playground-site/ensure-playground-site-is-selected.tsx
+++ b/packages/playground/website/src/components/ensure-playground-site/ensure-playground-site-is-selected.tsx
@@ -17,7 +17,10 @@ import { redirectTo } from '../../lib/state/url/router';
 import { logger } from '@php-wasm/logger';
 import { usePrevious } from '../../lib/hooks/use-previous';
 import { modalSlugs } from '../layout';
-import { setActiveModal } from '../../lib/state/redux/slice-ui';
+import {
+	setActiveModal,
+	setActiveSiteError,
+} from '../../lib/state/redux/slice-ui';
 import { selectClientBySiteSlug } from '../../lib/state/redux/slice-clients';
 import { randomSiteName } from '../../lib/state/redux/random-site-name';
 
@@ -158,8 +161,18 @@ async function createNewTemporarySite(
 	const siteName = requestedSiteSlug
 		? deriveSiteNameFromSlug(requestedSiteSlug)
 		: randomSiteName();
-	const newSiteInfo = await dispatch(
+	const { site, blueprintResolutionFailed } = await dispatch(
 		setTemporarySiteSpec(siteName, new URL(window.location.href))
 	);
-	await dispatch(setActiveSite(newSiteInfo.slug));
+	await dispatch(setActiveSite(site.slug));
+	if (blueprintResolutionFailed) {
+		dispatch(
+			setActiveSiteError({
+				error: 'blueprint-resolution-failed',
+				context: {
+					blueprintResolution: blueprintResolutionFailed,
+				},
+			})
+		);
+	}
 }
diff --git a/packages/playground/website/src/components/playground-viewport/index.tsx b/packages/playground/website/src/components/playground-viewport/index.tsx
index 23be0e3951..9b5b47cad9 100644
--- a/packages/playground/website/src/components/playground-viewport/index.tsx
+++ b/packages/playground/website/src/components/playground-viewport/index.tsx
@@ -4,19 +4,24 @@ import css from './style.module.css';
 import BrowserChrome from '../browser-chrome';
 import {
 	selectActiveSiteError,
+	selectActiveSiteErrorContext,
 	useActiveSite,
 	useAppDispatch,
 	useAppSelector,
 } from '../../lib/state/redux/store';
 import { removeClientInfo } from '../../lib/state/redux/slice-clients';
 import { bootSiteClient } from '../../lib/state/redux/boot-site-client';
-import type { SiteError } from '../../lib/state/redux/slice-ui';
+import type {
+	ActiveSiteErrorContext,
+	SiteError,
+} from '../../lib/state/redux/slice-ui';
 import { Button, Spinner } from '@wordpress/components';
 import {
 	removeSite,
 	selectSiteBySlug,
 	selectSitesLoaded,
 	selectTemporarySites,
+	DEFAULT_WELCOME_BLUEPRINT_URL,
 } from '../../lib/state/redux/slice-sites';
 import classNames from 'classnames';
 
@@ -202,12 +207,17 @@ export const JustViewport = function JustViewport({
 	}, [siteSlug, iframeRef, runtimeConfigString]);
 
 	const error = useAppSelector(selectActiveSiteError);
+	const errorContext = useAppSelector(selectActiveSiteErrorContext);
 
 	if (error) {
 		return (
 			<div className={css.siteError}>
 				<div className={css.siteErrorContent}>
-					<SiteErrorMessage error={error} siteSlug={siteSlug} />
+					<SiteErrorMessage
+						error={error}
+						siteSlug={siteSlug}
+						errorContext={errorContext}
+					/>
 				</div>
 			</div>
 		);
@@ -226,11 +236,88 @@ export const JustViewport = function JustViewport({
 function SiteErrorMessage({
 	error,
 	siteSlug,
+	errorContext,
 }: {
 	error: SiteError;
 	siteSlug: string;
+	errorContext?: ActiveSiteErrorContext;
 }) {
 	const dispatch = useAppDispatch();
+	if (error === 'blueprint-resolution-failed') {
+		const blueprintError = errorContext?.blueprintResolution;
+		const attemptedUrl =
+			blueprintError?.attemptedUrl || DEFAULT_WELCOME_BLUEPRINT_URL;
+		const rawStatusText =
+			typeof blueprintError?.statusText === 'string'
+				? blueprintError.statusText.trim()
+				: undefined;
+		const statusSummary =
+			typeof blueprintError?.httpStatus === 'number'
+				? `HTTP ${blueprintError.httpStatus}${
+						rawStatusText ? ` ${rawStatusText}` : ''
+				  }`
+				: rawStatusText;
+		const trimmedMessage =
+			typeof blueprintError?.message === 'string'
+				? blueprintError.message.trim()
+				: undefined;
+		const shouldShowMessage =
+			trimmedMessage &&
+			trimmedMessage.length > 0 &&
+			trimmedMessage !== statusSummary &&
+			trimmedMessage !== attemptedUrl;
+		return (
+			<>
+				<h1>We couldn't load that Blueprint</h1>
+				<p>
+					WordPress Playground couldn't load the Blueprint below. The
+					file might be unavailable or invalid.
+				</p>
+				{attemptedUrl ? (
+					<p className={css.blueprintUrlWrapper}>
+						<a
+							className={css.blueprintUrl}
+							target="_blank"
+							rel="noopener noreferrer"
+							href={attemptedUrl}
+						>
+							{attemptedUrl}
+						</a>
+					</p>
+				) : null}
+				{statusSummary ? (
+					<p className={css.blueprintStatus}>{statusSummary}</p>
+				) : null}
+				{shouldShowMessage ? <p>{trimmedMessage}</p> : null}
+				<p>
+					Reload without a Blueprint to start with a blank WordPress
+					site.
+				</p>
+				<Button
+					className={css.actionButton}
+					variant="primary"
+					onClick={() => {
+						const url = new URL(window.location.href);
+						url.searchParams.delete('blueprint-url');
+						url.searchParams.delete('import-wxr');
+						url.searchParams.delete('import-content');
+						url.searchParams.delete('import-site');
+						url.searchParams.delete('plugin');
+						url.searchParams.delete('theme');
+						url.searchParams.delete('php');
+						url.searchParams.delete('wp');
+						url.searchParams.delete('language');
+						url.searchParams.delete('networking');
+						url.searchParams.delete('site-slug');
+						url.hash = '';
+						window.location.href = url.toString();
+					}}
+				>
+					reload without a Blueprint
+				</Button>
+			</>
+		);
+	}
 	if (
 		error === 'directory-handle-not-found-in-indexeddb' ||
 		error === 'directory-handle-permission-denied'
diff --git a/packages/playground/website/src/components/playground-viewport/style.module.css b/packages/playground/website/src/components/playground-viewport/style.module.css
index 4a40c29cf9..9e3d191067 100644
--- a/packages/playground/website/src/components/playground-viewport/style.module.css
+++ b/packages/playground/website/src/components/playground-viewport/style.module.css
@@ -37,6 +37,23 @@
 	}
 }
 
+.blueprint-url-wrapper {
+	margin-bottom: 15px;
+	word-break: break-word;
+	overflow-wrap: anywhere;
+}
+
+.blueprint-url {
+	display: inline-block;
+	word-break: break-word;
+	overflow-wrap: anywhere;
+}
+
+.blueprintStatus {
+	font-weight: 600;
+	margin-bottom: 15px;
+}
+
 .hidden {
 	display: none;
 }
diff --git a/packages/playground/website/src/lib/state/redux/boot-site-client.ts b/packages/playground/website/src/lib/state/redux/boot-site-client.ts
index 7f5e87e613..810ff6d993 100644
--- a/packages/playground/website/src/lib/state/redux/boot-site-client.ts
+++ b/packages/playground/website/src/lib/state/redux/boot-site-client.ts
@@ -57,9 +57,9 @@ export function bootSiteClient(
 			} catch (e) {
 				logger.error(e);
 				dispatch(
-					setActiveSiteError(
-						'directory-handle-not-found-in-indexeddb'
-					)
+					setActiveSiteError({
+						error: 'directory-handle-not-found-in-indexeddb',
+					})
 				);
 				return;
 			}
@@ -82,13 +82,17 @@ export function bootSiteClient(
 				logger.error(e);
 				if (e instanceof DOMException && e.name === 'NotFoundError') {
 					dispatch(
-						setActiveSiteError(
-							'directory-handle-not-found-in-indexeddb'
-						)
+						setActiveSiteError({
+							error: 'directory-handle-not-found-in-indexeddb',
+						})
 					);
 					return;
 				}
-				dispatch(setActiveSiteError('directory-handle-unknown-error'));
+				dispatch(
+					setActiveSiteError({
+						error: 'directory-handle-unknown-error',
+					})
+				);
 				return;
 			}
 		}
@@ -197,9 +201,11 @@ export function bootSiteClient(
 				(e as any).name === 'ArtifactExpiredError' ||
 				(e as any).originalErrorClassName === 'ArtifactExpiredError'
 			) {
-				dispatch(setActiveSiteError('github-artifact-expired'));
+				dispatch(
+					setActiveSiteError({ error: 'github-artifact-expired' })
+				);
 			} else {
-				dispatch(setActiveSiteError('site-boot-failed'));
+				dispatch(setActiveSiteError({ error: 'site-boot-failed' }));
 				dispatch(setActiveModal(modalSlugs.ERROR_REPORT));
 			}
 			return;
diff --git a/packages/playground/website/src/lib/state/redux/slice-sites.ts b/packages/playground/website/src/lib/state/redux/slice-sites.ts
index b776f5d137..023581036a 100644
--- a/packages/playground/website/src/lib/state/redux/slice-sites.ts
+++ b/packages/playground/website/src/lib/state/redux/slice-sites.ts
@@ -20,6 +20,7 @@ import {
 	applyQueryOverrides,
 } from '../url/resolve-blueprint-from-url';
 import { logger } from '@php-wasm/logger';
+import type { ActiveSiteErrorContext } from './slice-ui';
 
 /**
  * The Site model used to represent a site within Playground.
@@ -238,6 +239,18 @@ export function removeSite(slug: string) {
  * @param siteInfo The site info to add.
  * @returns
  */
+export const DEFAULT_WELCOME_BLUEPRINT_URL =
+	'https://raw.githubusercontent.com/WordPress/blueprints/refs/heads/trunk/blueprints/welcome/blueprint.json';
+
+export interface SetTemporarySiteSpecResult {
+	site: SiteInfo;
+	blueprintResolutionFailed?: ActiveSiteErrorContext['blueprintResolution'];
+}
+
+type BlueprintResolutionFailure = NonNullable<
+	ActiveSiteErrorContext['blueprintResolution']
+>;
+
 export function setTemporarySiteSpec(
 	siteName: string,
 	playgroundUrlWithQueryApiArgs: URL
@@ -245,7 +258,7 @@ export function setTemporarySiteSpec(
 	return async (
 		dispatch: PlaygroundDispatch,
 		getState: () => PlaygroundReduxState
-	) => {
+	): Promise<SetTemporarySiteSpecResult> => {
 		const newSiteUrlParams = {
 			searchParams: parseSearchParams(
 				playgroundUrlWithQueryApiArgs.searchParams
@@ -261,7 +274,7 @@ export function setTemporarySiteSpec(
 				JSON.stringify(currentTemporarySite.originalUrlParams) ===
 				JSON.stringify(newSiteUrlParams)
 			) {
-				return currentTemporarySite;
+				return { site: currentTemporarySite };
 			}
 		}
 
@@ -275,10 +288,12 @@ export function setTemporarySiteSpec(
 		}
 
 		// Then create a new temporary site
-		const defaultBlueprint =
-			'https://raw.githubusercontent.com/WordPress/blueprints/refs/heads/trunk/blueprints/welcome/blueprint.json';
+		const defaultBlueprint = DEFAULT_WELCOME_BLUEPRINT_URL;
 
 		let resolvedBlueprint: ResolvedBlueprint | undefined = undefined;
+		let blueprintResolutionFailed:
+			| SetTemporarySiteSpecResult['blueprintResolutionFailed']
+			| undefined;
 		try {
 			resolvedBlueprint = await resolveBlueprintFromURL(
 				playgroundUrlWithQueryApiArgs,
@@ -286,9 +301,28 @@ export function setTemporarySiteSpec(
 			);
 		} catch (e) {
 			logger.error(
-				'Error resolving blueprint, fallink back to a blank blueprint.',
+				'Error resolving blueprint, falling back to a blank blueprint.',
 				e
 			);
+			const hasBlueprintQuery =
+				playgroundUrlWithQueryApiArgs.searchParams.has('blueprint-url');
+			const hasFragment =
+				(playgroundUrlWithQueryApiArgs.hash || '').length > 1;
+			const attemptedBlueprintUrl = hasBlueprintQuery
+				? playgroundUrlWithQueryApiArgs.searchParams.get(
+						'blueprint-url'
+				  )!
+				: !hasFragment
+				? defaultBlueprint
+				: undefined;
+			const attemptedUrl =
+				attemptedBlueprintUrl || playgroundUrlWithQueryApiArgs.href;
+			blueprintResolutionFailed = buildBlueprintResolutionFailureDetails(
+				e,
+				attemptedUrl
+			) || {
+				attemptedUrl,
+			};
 			// TODO: This is a hack – we are just abusing a URL-oriented
 			// function to create a completely blank Blueprint. Let's fix this by
 			// making default creation first-class.
@@ -325,10 +359,81 @@ export function setTemporarySiteSpec(
 		};
 		dispatch(sitesSlice.actions.addSite(newSiteInfo));
 		dispatch(sitesSlice.actions.setFirstTemporarySiteCreated());
-		return newSiteInfo;
+		return {
+			site: newSiteInfo,
+			blueprintResolutionFailed,
+		};
 	};
 }
 
+function buildBlueprintResolutionFailureDetails(
+	error: unknown,
+	attemptedUrl?: string
+): BlueprintResolutionFailure | undefined {
+	const details: BlueprintResolutionFailure = {};
+	if (attemptedUrl) {
+		details.attemptedUrl = attemptedUrl;
+	}
+
+	const errorLike = error as {
+		status?: unknown;
+		statusCode?: unknown;
+		statusText?: unknown;
+		response?: { status?: unknown; statusText?: unknown };
+		cause?: { status?: unknown; statusText?: unknown };
+		message?: unknown;
+	};
+
+	const statusCandidates = [
+		errorLike?.status,
+		errorLike?.response?.status,
+		errorLike?.cause?.status,
+		errorLike?.statusCode,
+	];
+	for (const candidate of statusCandidates) {
+		if (
+			typeof candidate === 'number' &&
+			Number.isFinite(candidate) &&
+			candidate > 0
+		) {
+			details.httpStatus = candidate;
+			break;
+		}
+	}
+
+	const statusTextCandidates = [
+		errorLike?.statusText,
+		errorLike?.response?.statusText,
+		errorLike?.cause?.statusText,
+	];
+	for (const candidate of statusTextCandidates) {
+		if (typeof candidate === 'string' && candidate.trim()) {
+			details.statusText = candidate.trim();
+			break;
+		}
+	}
+
+	let message: string | undefined;
+	if (typeof errorLike?.message === 'string') {
+		message = errorLike.message;
+	} else if (typeof error === 'string') {
+		message = error;
+	}
+
+	if (message) {
+		const trimmedMessage = message.trim();
+		if (
+			trimmedMessage &&
+			trimmedMessage !== details.statusText &&
+			trimmedMessage !== attemptedUrl
+		) {
+			details.message = trimmedMessage;
+		}
+	}
+
+	return Object.keys(details).length ? details : undefined;
+}
+
 function parseSearchParams(searchParams: URLSearchParams) {
 	const params: Record<string, any> = {};
 	for (const key of searchParams.keys()) {
diff --git a/packages/playground/website/src/lib/state/redux/slice-ui.ts b/packages/playground/website/src/lib/state/redux/slice-ui.ts
index 672a3fe7ab..f597baacdf 100644
--- a/packages/playground/website/src/lib/state/redux/slice-ui.ts
+++ b/packages/playground/website/src/lib/state/redux/slice-ui.ts
@@ -8,13 +8,26 @@ export type SiteError =
 	| 'directory-handle-unknown-error'
 	// @TODO: Improve name?
 	| 'site-boot-failed'
-	| 'github-artifact-expired';
+	| 'github-artifact-expired'
+	| 'blueprint-resolution-failed';
+
+export interface BlueprintResolutionErrorContext {
+	attemptedUrl?: string;
+	httpStatus?: number;
+	statusText?: string;
+	message?: string;
+}
+
+export interface ActiveSiteErrorContext {
+	blueprintResolution?: BlueprintResolutionErrorContext;
+}
 
 export type SiteManagerSection = 'sidebar' | 'site-details' | 'blueprints';
 export interface UIState {
 	activeSite?: {
 		slug: string;
 		error?: SiteError;
+		context?: ActiveSiteErrorContext;
 	};
 	activeModal: string | null;
 	offline: boolean;
@@ -68,9 +81,16 @@ const uiSlice = createSlice({
 				  }
 				: undefined;
 		},
-		setActiveSiteError: (state, action: PayloadAction<SiteError>) => {
+		setActiveSiteError: (
+			state,
+			action: PayloadAction<{
+				error: SiteError;
+				context?: ActiveSiteErrorContext;
+			}>
+		) => {
 			if (state.activeSite) {
-				state.activeSite.error = action.payload;
+				state.activeSite.error = action.payload.error;
+				state.activeSite.context = action.payload.context;
 			}
 		},
 		setActiveModal: (state, action: PayloadAction<string | null>) => {
diff --git a/packages/playground/website/src/lib/state/redux/store.ts b/packages/playground/website/src/lib/state/redux/store.ts
index 3ba04ed195..94385b63ed 100644
--- a/packages/playground/website/src/lib/state/redux/store.ts
+++ b/packages/playground/website/src/lib/state/redux/store.ts
@@ -1,5 +1,5 @@
 import { configureStore, createSelector } from '@reduxjs/toolkit';
-import type { SiteError } from './slice-ui';
+import type { ActiveSiteErrorContext, SiteError } from './slice-ui';
 import uiReducer, {
 	__internal_uiSlice,
 	listenToOnlineOfflineEventsMiddleware,
@@ -89,6 +89,11 @@ export const selectActiveSiteError = (
 ): SiteError | undefined =>
 	state.ui.activeSite?.slug ? state.ui.activeSite.error : undefined;
 
+export const selectActiveSiteErrorContext = (
+	state: PlaygroundReduxState
+): ActiveSiteErrorContext | undefined =>
+	state.ui.activeSite?.slug ? state.ui.activeSite.context : undefined;
+
 export const useActiveSite = () => useAppSelector(selectActiveSite);
 
 export const setActiveSite = (slug: string | undefined) => {