diff --git a/pxtlib/service.ts b/pxtlib/service.ts
index 6e49c7c9fbdc..2d5a2e060d6d 100644
--- a/pxtlib/service.ts
+++ b/pxtlib/service.ts
@@ -1839,6 +1839,7 @@ namespace ts.pxtc.service {
         imageUrl?: string;
         type?: ExtensionType;
         learnMoreUrl?: string;
+        installed?: boolean;
 
         pkgConfig?: pxt.PackageConfig; // Added if the type is Bundled
         repo?: pxt.github.GitRepo; //Added if the type is Github VVN TODO ADD THIS
diff --git a/react-common/components/extensions/ExtensionCard.tsx b/react-common/components/extensions/ExtensionCard.tsx
index 2ee26b478b5c..ab2ccc82206c 100644
--- a/react-common/components/extensions/ExtensionCard.tsx
+++ b/react-common/components/extensions/ExtensionCard.tsx
@@ -10,9 +10,11 @@ export interface ExtensionCardProps<U> {
     imageUrl?: string;
     learnMoreUrl?: string;
     label?: string;
+    labelClass?: string;
     onClick?: (value: U) => void;
     extension?: U;
     loading?: boolean;
+    installed?: boolean;
     showDisclaimer?: boolean
 }
 
@@ -23,9 +25,11 @@ export const ExtensionCard = <U,>(props: ExtensionCardProps<U>) => {
         imageUrl,
         learnMoreUrl,
         label,
+        labelClass,
         onClick,
         extension,
         loading,
+        installed,
         showDisclaimer
     } = props;
 
@@ -34,15 +38,20 @@ export const ExtensionCard = <U,>(props: ExtensionCardProps<U>) => {
     }
 
     const id = pxt.Util.guidGen();
+    const cardLabel = installed ? lf("Installed") : label;
+    const cardLabelClass = installed ? classList("installed", labelClass) : labelClass;
+    const descriptionId = id + "-description";
+    const statusId = cardLabel ? id + "-status" : undefined;
 
     return <>
         <Card
-            className={classList("common-extension-card", loading && "loading")}
+            className={classList("common-extension-card", loading && "loading", installed && "installed")}
             onClick={onCardClick}
             ariaLabelledBy={id + "-title"}
-            ariaDescribedBy={id + "-description"}
+            ariaDescribedBy={classList(descriptionId, statusId)}
             tabIndex={onClick && 0}
-            label={label}>
+            label={cardLabel}
+            labelClass={cardLabelClass}>
             <div className="common-extension-card-contents">
                 {!loading && <>
                     {imageUrl && <LazyImage src={imageUrl} alt={title} />}
@@ -50,10 +59,11 @@ export const ExtensionCard = <U,>(props: ExtensionCardProps<U>) => {
                         {title}
                     </div>
                     <div className="common-extension-card-description">
-                        <div id={id + "-description"}>
+                        <div id={descriptionId}>
                             {description}
                         </div>
                     </div>
+                    {cardLabel && <div id={statusId} className="sr-only">{cardLabel}</div>}
                     {(showDisclaimer || learnMoreUrl) &&
                         <div className="common-extension-card-extra-content">
                             {showDisclaimer && lf("User-provided extension, not endorsed by Microsoft.")}
diff --git a/react-common/styles/extensions/ExtensionCard.less b/react-common/styles/extensions/ExtensionCard.less
index 9d04d824255c..aee50bffc390 100644
--- a/react-common/styles/extensions/ExtensionCard.less
+++ b/react-common/styles/extensions/ExtensionCard.less
@@ -58,6 +58,12 @@
         border-bottom-right-radius: 0.5rem;
     }
 
+    .common-card-label.installed {
+        color: var(--pxt-colors-green-foreground);
+        background-color: var(--pxt-colors-green-background);
+        border-color: var(--pxt-colors-green-hover);
+    }
+
     a.link-button {
         float: right;
         position: relative;
@@ -94,6 +100,14 @@
     }
 }
 
+.common-extension-card.installed {
+    overflow: visible;
+
+    .common-card-body {
+        overflow: hidden;
+    }
+}
+
 /****************************************************
  *                 High Contrast                    *
  ****************************************************/
@@ -102,5 +116,11 @@
     .common-extension-card {
         border-color: @highContrastTextColor;
         background-color: @highContrastBackgroundColor;
+
+        .common-card-label.installed {
+            color: @highContrastBackgroundColor;
+            background-color: @highContrastTextColor;
+            border-color: @highContrastTextColor;
+        }
     }
 }
diff --git a/webapp/src/extensionsBrowser.tsx b/webapp/src/extensionsBrowser.tsx
index 723889559dce..8bb88da921d1 100644
--- a/webapp/src/extensionsBrowser.tsx
+++ b/webapp/src/extensionsBrowser.tsx
@@ -13,7 +13,7 @@ import { Modal } from "../../react-common/components/controls/Modal";
 import { classList } from "../../react-common/components/util";
 import { TabList, TabListProps } from "../../react-common/components/controls/TabList";
 
-type ExtensionMeta = pxtc.service.ExtensionMeta;
+type ExtensionMeta = pxtc.service.ExtensionMeta & { installed?: boolean };
 const ExtensionType = pxtc.service.ExtensionType;
 type EmptyCard = { name: string, loading?: boolean }
 const emptyCard: EmptyCard = { name: "", loading: true }
@@ -58,6 +58,76 @@ export const ExtensionsBrowser = (props: ExtensionsProps) => {
         }
     }, [searchFor])
 
+    function currentProjectDependencies(): pxt.Map<string> {
+        return pkg.mainPkg?.config?.dependencies || {};
+    }
+
+    function dependencyVersions(): string[] {
+        const dependencies = currentProjectDependencies();
+        return Object.keys(dependencies).map(dep => dependencies[dep]);
+    }
+
+    function isDependencyInstalled(name?: string): boolean {
+        return !!name && !!currentProjectDependencies()[name];
+    }
+
+    function normalizedPublishedScriptId(version: string): string | undefined {
+        if (!version) return undefined;
+        if (version.slice(0, 4) === "pub:") return version.slice(4);
+        return pxt.Cloud.parseScriptId(version);
+    }
+
+    function githubReposMatch(a?: pxt.github.ParsedRepo, b?: pxt.github.ParsedRepo): boolean {
+        if (!a || !b) return false;
+        if (a.fileName || b.fileName)
+            return a.fullName.toLowerCase() === b.fullName.toLowerCase();
+        return a.slug.toLowerCase() === b.slug.toLowerCase();
+    }
+
+    function isGithubExtensionInstalled(extensionInfo: ExtensionMeta): boolean {
+        const extensionRepos: pxt.github.ParsedRepo[] = [];
+        const repoIds = [extensionInfo.repo?.fullName, extensionInfo.fullRepo];
+        repoIds.forEach(repoId => {
+            const parsed = repoId && pxt.github.parseRepoId(repoId);
+            if (parsed) extensionRepos.push(parsed);
+        });
+        if (!extensionRepos.length) return false;
+
+        return dependencyVersions().some(version => {
+            const dependencyRepo = pxt.github.parseRepoId(version);
+            return extensionRepos.some(repo => githubReposMatch(repo, dependencyRepo));
+        });
+    }
+
+    function isShareScriptInstalled(scriptInfo?: pxt.Cloud.JsonScript): boolean {
+        if (!scriptInfo?.id) return false;
+        return dependencyVersions().some(version => normalizedPublishedScriptId(version) === scriptInfo.id);
+    }
+
+    function isLocalExtensionInstalled(header: pxt.workspace.Header): boolean {
+        return dependencyVersions().some(version => version === `workspace:${header.id}`);
+    }
+
+    function isExtensionInstalled(extensionInfo: ExtensionMeta): boolean {
+        switch (extensionInfo.type) {
+            case ExtensionType.Bundled:
+                return isDependencyInstalled(extensionInfo.pkgConfig?.name || extensionInfo.name);
+            case ExtensionType.Github:
+                return isGithubExtensionInstalled(extensionInfo) || isDependencyInstalled(extensionInfo.name);
+            case ExtensionType.ShareScript:
+                return isShareScriptInstalled(extensionInfo.scriptInfo) || isDependencyInstalled(extensionInfo.name);
+            default:
+                return isDependencyInstalled(extensionInfo.name);
+        }
+    }
+
+    function withInstalledFlag<T extends ExtensionMeta>(extensionInfo: T): T {
+        return {
+            ...extensionInfo,
+            installed: isExtensionInstalled(extensionInfo)
+        };
+    }
+
     /**
      * Github search
      */
@@ -106,10 +176,17 @@ export const ExtensionsBrowser = (props: ExtensionsProps) => {
         if (!newExtension) {
             return;
         }
-        const addedExtensions = allExtensions;
+        const addedExtensions = new Map(allExtensions);
         newExtension.forEach(e => {
-            if (!addedExtensions.has(e.name.toLowerCase())) {
-                addedExtensions.set(e.name.toLowerCase(), e)
+            const extensionWithStatus = withInstalledFlag(e);
+            if (!addedExtensions.has(extensionWithStatus.name.toLowerCase())) {
+                addedExtensions.set(extensionWithStatus.name.toLowerCase(), extensionWithStatus)
+            }
+            if (extensionWithStatus.fullRepo && !addedExtensions.has(extensionWithStatus.fullRepo.toLowerCase())) {
+                addedExtensions.set(extensionWithStatus.fullRepo.toLowerCase(), extensionWithStatus)
+            }
+            if (extensionWithStatus.repo?.fullName && !addedExtensions.has(extensionWithStatus.repo.fullName.toLowerCase())) {
+                addedExtensions.set(extensionWithStatus.repo.fullName.toLowerCase(), extensionWithStatus)
             }
         })
         setAllExtensions(addedExtensions);
@@ -308,7 +385,7 @@ export const ExtensionsBrowser = (props: ExtensionsProps) => {
     }
 
     function parseGithubRepo(r: pxt.github.GitRepo): ExtensionMeta {
-        return {
+        return withInstalledFlag({
             name: ghName(r),
             displayName: r.displayName,
             type: ExtensionType.Github,
@@ -316,17 +393,17 @@ export const ExtensionsBrowser = (props: ExtensionsProps) => {
             repo: r,
             description: r.description,
             fullRepo: r.fullName
-        }
+        })
     }
 
     function parseShareScript(s: pxt.Cloud.JsonScript): ExtensionMeta {
-        return {
+        return withInstalledFlag({
             name: s.name,
             type: ExtensionType.ShareScript,
             imageUrl: s.thumb ? `${pxt.Cloud.apiRoot}/${s.id}/thumb` : undefined,
             description: s.description,
             scriptInfo: s,
-        }
+        })
     }
 
 
@@ -364,7 +441,7 @@ export const ExtensionsBrowser = (props: ExtensionsProps) => {
     }
 
     function packageConfigToExtensionMeta(p: pxt.PackageConfig): ExtensionMeta {
-        return {
+        return withInstalledFlag({
             name: p.name,
             displayName: p.displayName,
             imageUrl: p.icon,
@@ -372,7 +449,7 @@ export const ExtensionsBrowser = (props: ExtensionsProps) => {
             learnMoreUrl: `/reference/${p.name}`,
             pkgConfig: p,
             description: p.description
-        }
+        })
     }
 
     function fetchBundled(): Map<string, ExtensionMeta> {
@@ -385,7 +462,6 @@ export const ExtensionsBrowser = (props: ExtensionsProps) => {
             .filter(pk => !pk.searchOnly || searchFor?.length != 0)
             .filter(pk => pk.name != "core")
             .filter(pk => false == !!pk.core) // show core in "boards" mode
-            .filter(pk => !pkg.mainPkg.deps[pk.name] || pkg.mainPkg.deps[pk.name].cppOnly) // don't show package already referenced in extensions
             .sort((a, b) => {
                 // core first
                 if (a.core != b.core)
@@ -457,7 +533,7 @@ export const ExtensionsBrowser = (props: ExtensionsProps) => {
     function ExtensionMetaCard(props: {
         extensionInfo: ExtensionMeta & EmptyCard,
     }) {
-        const { extensionInfo } = props;
+        const extensionInfo = withInstalledFlag(props.extensionInfo);
         const {
             description,
             fullRepo,
@@ -478,6 +554,7 @@ export const ExtensionsBrowser = (props: ExtensionsProps) => {
             onClick={installExtension}
             learnMoreUrl={learnMoreUrl || (fullRepo ? `/pkg/${fullRepo}` : undefined)}
             loading={loading}
+            installed={extensionInfo.installed}
             label={pxt.isPkgBeta(extensionInfo) ? lf("Beta") : undefined}
             showDisclaimer={type != ExtensionType.Bundled && repo?.status != pxt.github.GitRepoStatus.Approved}
         />;
@@ -578,16 +655,18 @@ export const ExtensionsBrowser = (props: ExtensionsProps) => {
                                 )
                             }
                             {currentTab === LOCAL_TAG_ID &&
-                                extensionsInDevelopment.map((p, index) =>
-                                    <ExtensionCard
+                                extensionsInDevelopment.map((p, index) => {
+                                    const installed = isLocalExtensionInstalled(p);
+                                    return <ExtensionCard
                                         key={`local:${index}`}
                                         title={p.name}
                                         description={lf("Local copy of {0} hosted on github.com", p.githubId)}
                                         imageUrl={p.icon}
                                         extension={p}
                                         onClick={addLocal}
-                                    />
-                                )
+                                        installed={installed}
+                                    />;
+                                })
                             }
                             {currentTab !== RECOMMENDED_TAG_ID && currentTab !== LOCAL_TAG_ID &&
                                 extensionsToShow?.map(