* feat(events): DOM-model on* semantics with addEventListener/removeEventListener
Fixes#551 (useHostStyles broken: fonts clobber theme/CSS variables)
Fixes#225 (user onhostcontextchanged and SDK hooks mutually exclusive)
The on* setters now follow the DOM event model:
- Replace semantics (like el.onclick) with getters
- Coexist with addEventListener/removeEventListener listeners
- Both channels fire on dispatch: on* handler then listeners
Introduces ProtocolWithEvents base class between Protocol and
App/AppBridge. Each notification event gets a slot with two independent
channels (singular on* handler + addEventListener listener array).
useHostStyles hooks now use addEventListener with proper cleanup,
so they compose correctly with user on* handlers.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
* Fix typedoc validation warnings
- Export AppEventMap, AppBridgeEventMap, ProtocolWithEvents so they
appear in generated docs (they're part of public addEventListener
signatures)
- Move AppBridgeEventMap above the AppBridge class JSDoc — it had been
inserted between the doc block and the class, orphaning the AppBridge
docs onto the wrong type
- Drop @param callback tags from on* getter/setter pairs — typedoc
attaches the doc block to the getter signature which has no params
- Add MethodSchema to intentionallyNotExported (internal zod helper
referenced by the now-documented eventSchemas field)
---------
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Reverts the fullscreen displayMode guard added in #567. Skipping
size-changed measurement during fullscreen caused apps to not receive
an initial size report after the transition, breaking layout for some
apps.
* Fix auto-resize destroying horizontal scroll positions
The setupSizeChangedNotifications method temporarily sets
html.style.width to 'fit-content' to measure intrinsic content width.
For responsive apps that derive width from their container (width: 100%,
flex: 1, etc.), fit-content resolves to 0px. The synchronous reflow at
0px causes browsers to clamp scrollLeft on all horizontal scroll
containers to 0, permanently destroying their scroll positions.
Replace the fit-content width measurement with window.innerWidth. The
height measurement (max-content) is preserved since hosts rely on it.
Neither the iOS nor web host uses the width value from size-changed
notifications, so this change has no functional impact on hosts while
fixing scroll position clamping for all MCP apps with horizontal scroll
views.
* Skip size-changed measurement during fullscreen
Hosts determine the container size in fullscreen mode, so size-changed
notifications are not needed. The temporary max-content height override
used for measurement causes visible vertical jitter during animated
fullscreen transitions by briefly reflowing the document on every frame.
The generated schemas compose with schemas imported from
@modelcontextprotocol/sdk/types.js (e.g. z.array(ContentBlockSchema)).
The SDK constructs its schemas via `import * as z from 'zod/v4'`, but
our generated schema.ts used `import { z } from "zod"` — which returns
the v3 API when the consumer has zod 3.25.x installed.
Mixing v3-created and v4-created schema instances throws at parse time
with errors like `keyValidator._parse is not a function` because zod v4
dropped the `_parse` / `_parseSync` internals that v3 wrappers call.
This was masked before #534 because zod was bundled — all schema
creation shared the same inlined zod copy. Externalizing zod exposed
the mismatch on consumers pinned to zod 3.x (e.g. anthropics/apps).
The `zod/v4` subpath is exported by both zod 3.25+ and zod 4.x, so the
existing peerDependency range `^3.25.0 || ^4.0.0` is preserved.
https://claude.ai/code/session_013xQUegrvVGct5xpqeSL5av
Co-authored-by: Claude <noreply@anthropic.com>
Follow-up to #470. Matches MCP SDK Client.listResources(params?) signature
so callers can omit the empty {} for the common case.
Also reflows a line in app-bridge.test.ts that prettier flagged.
fit-content clamps to the containing block's available size. For <html>,
that's the iframe viewport, so when content exceeds the viewport height
the SDK reported the viewport height instead of the true content height,
causing internal scrolling instead of iframe growth.
max-content has no available-space constraint and correctly reports the
intrinsic content height in both directions (shrink and grow). Width
stays fit-content to preserve responsive wrapping.
Replace custom {filename, content, mimeType, encoding} params with
standard MCP resource types: EmbeddedResource for inline content and
ResourceLink for host-resolved references.
New params shape:
params: { contents: (EmbeddedResource | ResourceLink)[] }
This reuses existing MCP primitives instead of inventing new ones,
and enables hosts to show resource 'bubbles' or resolve ResourceLink
URIs via resources/read on the MCP server.
Add a new ui/download-file JSON-RPC request that allows MCP App views to
request file downloads through the host. Since MCP Apps run in sandboxed
iframes where direct downloads are blocked (allow-downloads not set),
this provides a host-mediated mechanism for file exports.
Spec changes (draft):
- Add ui/download-file request to Requests (View → Host) section
- Add downloadFile capability to HostCapabilities
- Document host behavior requirements (confirmation dialog, filename
sanitization, base64 decoding, size limits)
SDK changes:
- Add McpUiDownloadFileRequest/Result interfaces to spec.types.ts
- Add downloadFile() method to App class
- Add ondownloadfile setter to AppBridge class
- Add DOWNLOAD_FILE_METHOD constant
- Generate Zod schemas
Example:
- Add download demo to integration-server (exports JSON with server time)
- Capability check: only shows download button when host advertises
downloadFile capability
Based on developer feedback requesting file export capabilities for
visualization tools, document editors, and data analysis apps.
* fix: guard against double-connect in App and AppBridge (#429)
Calling connect() twice on the same transport instance caused the MCP
SDK's Protocol class to chain onmessage handlers, so each incoming
message was processed twice. This made incoming responses get consumed
by the first processing (resolving the handler) and then trigger a
spurious "Received a response for an unknown message ID" error on the
second processing pass, since the handler was already removed from the
response map.
Add an explicit guard in both App.connect() and AppBridge.connect() that
throws if the instance is already connected. This converts the silent
message-corruption into a clear, actionable error and prevents
downstream confusion.
Adds three regression tests:
- AppBridge.connect() throws when already connected
- App.connect() throws when already connected
- Demonstrates the double-processing root cause and verifies it is fixed
Fixes#429https://claude.ai/code/session_01XU3FW1TpjBkyRbkBUH5gqR
* test: replace redundant regression test with cleaner same-transport guard check
The previous third test in "double-connect guard" never actually attempted
a double-connect — it created fresh instances and verified normal operation,
which every other test already covers. The stray bridge.onupdatemodelcontext
and bridgeTransport.close() at the top were leftover noise.
Replace it with a focused test that verifies the guard fires even when
the caller passes the *same* transport object (not just a different one),
which is the exact scenario described in #429.
https://claude.ai/code/session_01XU3FW1TpjBkyRbkBUH5gqR
---------
Co-authored-by: Claude <noreply@anthropic.com>
Users frequently call callServerTool("tool_name", args) instead of the
correct callServerTool({ name: "tool_name", arguments: args }), resulting
in a silent/confusing failure. Detect this and throw immediately with
a message that shows the correct call shape.
Also fixes the incorrect example in examples/pdf-server/README.md that
demonstrated this same wrong usage pattern.
Fixes#386https://claude.ai/code/session_01GqAyN4Ux7svWoU2HqsSLZF
Co-authored-by: Claude <noreply@anthropic.com>
Tighten the parse-failure handler: silently ignore postMessage frames
where event.data?.jsonrpc !== "2.0" (i.e. not JSON-RPC at all — null,
undefined, a primitive, or an object from the host environment that
doesn't carry the jsonrpc field). Messages that do carry jsonrpc: "2.0"
but are otherwise malformed still surface via onerror so genuine protocol
errors aren't swallowed.
https://claude.ai/code/session_01DaJpUtSJf4hA7tnu3nJz8s
Co-authored-by: Claude <noreply@anthropic.com>
* Clarify spec and SDK: accept UIResourceMeta in both resources/list and resources/read
The spec defines UIResource with _meta.ui, implicitly as an extension of the Resource type (resources/list), but examples and practice place _meta.ui on TextResourceContents (resources/read). The registerAppResource helper accepts _meta.ui in its config (which ends up in resources/list), but examples only return said _meta.ui from resources/read — and current hosts might be just ignoring it.
This change:
- Adds a 'Metadata Location' subsection to the draft spec explicitly stating that _meta.ui is valid on both the resource listing entry AND the content item, with content-item taking precedence.
- Updates the spec example to show _meta on the resource declaration (resources/list).
- Updates the CSP construction example to reference both locations.
- Clarifies McpUiAppResourceConfig JSDoc: _meta here appears in resources/list and serves as a listing-level fallback for when content items omit _meta.ui.
- Fixes the map-server example comment that incorrectly stated _meta must only be on the content item.
* Add McpUiReadResourceResult type for UI metadata in resources/read
* basic-host: support UIResourceMeta fallback from resources/list
---------
Co-authored-by: Claude <noreply@anthropic.com>
The term "external" is misleading for MCP Apps because developers
typically interpret it as "third-party." However, MCP App HTML runs in
a sandboxed iframe with no same-origin server, so *all* origins must be
declared—including where your own bundled JS/CSS is served from. Using
"network" instead avoids this confusion and aligns with the detailed
explanations in `patterns.md` and `spec.types.ts`.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Adds a new section to the patterns guide explaining how to configure
Content Security Policy and CORS for MCP Apps that make network requests:
- CSP via `_meta.ui.csp` controls browser-side permissions (`connectDomains`,
`resourceDomains`)
- CORS via `_meta.ui.domain` provides a stable origin for API servers to
allowlist
Includes a type-checked example showing `computeAppDomainForClaude()` helper
that hashes an MCP server URL to create a stable `*.claudemcpcontent.com`
subdomain. Also adds `@see` links to `McpUiResourceMeta` and `McpUiResourceCsp`
in `registerAppResource` JSDoc.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Move the inline example from the `getUiCapability()` JSDoc to
`index.examples.ts` for type checking, following the pattern used
by other examples in the codebase.
The example now uses the correct MCP SDK API:
- `server.server.oninitialized` callback for post-initialization hook
- `server.server.getClientCapabilities()` to retrieve capabilities
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
- Rename "host styling" section to "host context" and add safe area
insets handling
- Replace abstract `renderLoadingUI`/`renderFinalUI` example with
concrete code preview pattern for `ontoolinputpartial`
- Rename callback parameter `params` → `ctx` for clarity across all
`onhostcontextchanged` handlers
- Add CSS snippet for fullscreen border-radius handling
- Expand display mode example to show `availableDisplayModes` check
- Fix minor typos and wording consistency
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
* chore: add stable spec release 2026-01-26
- Use git mv to copy specification from draft to specification/2026-01-26/apps.mdx (preserves history)
- Update status from 'Draft' to 'Stable (2026-01-26)'
- Add specification version table to README
- Update Resources section with links to both stable and draft specs
* chore: bump version to 1.0.0
- Update main package version from 0.4.2 to 1.0.0
- Update all example package versions to 1.0.0
- Regenerate package-lock.json
* prettier
* chore: align protocol version with spec release 2026-01-26
- Add 'Protocol Version: 2026-01-26' to spec header
- Update LATEST_PROTOCOL_VERSION from '2025-11-21' to '2026-01-26'
- Update spec examples to use '2026-01-26' protocol version
- Add '2025-11-21' to SUPPORTED_PROTOCOL_VERSIONS for backwards compatibility
* chore: update spec references to stable 2026-01-26
- Update typedoc.config.mjs navigation link
- Update docs/overview.md spec links (10 occurrences)
- Update plugins/mcp-apps/skills/create-mcp-app/SKILL.md spec link
- Update src/spec.types.ts @see links
- Update AGENTS.md spec path
- Regenerate src/generated/schema.ts with updated links
* chore: simplify versioning - first stable release
- Remove backwards compatibility version (2025-11-21) - this is the first stable release
- Remove redundant 'Protocol Version' header - spec version IS the protocol version
* chore: add history reference comment to stable spec
* Add appCapabilities.availableDisplayModes documentation to spec
Document the availableDisplayModes field in McpUiAppCapabilities that allows
apps to declare which display modes they support. This enables hosts to
compute the intersection of host and app capabilities and only offer
appropriate display mode controls.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
* Address PR review feedback
- Change "Guest UI" to "View" terminology
- Add "View" prefix to availableDisplayModes heading for disambiguation
- Remove intersection logic - host only checks its own supported modes
- Remove assumption that apps must support inline mode
- Simplify host behavior to honor/reject based on its own capabilities
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
* Add appCapabilities.availableDisplayModes to types
- Add `availableDisplayModes` field to `McpUiAppCapabilities` so apps can
declare which display modes they support
- Change `HostContext.availableDisplayModes` type from `string[]` to
`McpUiDisplayMode[]` for type safety
- Regenerate schemas
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
* Address Olivier's feedback - consolidate display mode docs
- Remove separate "App Capabilities" section for availableDisplayModes
- Add display mode requirements to existing ui/request-display-mode section:
- Host MUST NOT switch View to mode not in appCapabilities.availableDisplayModes
- Host MAY decline requests from Views that didn't declare modes
- View MUST declare supported modes during initialization
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
* Restore McpUiAppCapabilities docs and fix display mode clause
- Restore McpUiAppCapabilities interface documentation with availableDisplayModes
- Restore "View MUST check if the requested mode is in availableDisplayModes
from host context" clause that was accidentally removed
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
* Create unified Display Modes section
Consolidate all display mode documentation into a single section:
- Display mode types (inline, fullscreen, pip)
- Declaring support from View (appCapabilities.availableDisplayModes)
- Declaring support from Host (HostContext.availableDisplayModes)
- Requesting changes (ui/request-display-mode)
- Notifying changes (ui/notifications/host-context-changed)
- All MUST/SHOULD requirements for View and Host behavior
The ui/request-display-mode in Requests section now references
the Display Modes section for behavior details.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
* Remove mode coercion clause from display modes
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
* Regenerate schemas with correct version
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
---------
Co-authored-by: Claude <noreply@anthropic.com>
* feat(server): add hasUiSupport/getUiCapability for experimental+extensions
Support double-tagging for MCP Apps capability negotiation:
- Check both experimental and extensions fields in client capabilities
- Add hasUiSupport() to easily check if client supports MCP Apps
- Add getUiCapability() to retrieve the capability settings
- Update spec to document both capability locations
This enables forward compatibility as MCP transitions from experimental
to the extensions field (SEP-1724).
Claude-Generated-By: Claude Code (cli/claude-opus-4-5=100%)
Claude-Steers: 0
Claude-Permission-Prompts: 0
Claude-Escapes: 0
* fix: update @types/node version in package-lock.json
Replace invalid 22.19.5/22.19.6/22.19.7 versions with valid 22.19.3
* docs(spec): clarify hosts SHOULD double-tag, servers SHOULD check both
- Hosts SHOULD advertise capabilities in both experimental and extensions
- Servers SHOULD check both locations, preferring extensions when present
- Updated example to show double-tagging pattern
* chore: remove double-tagging recommendation, keep hasUiSupport helper
Reverts the spec changes that recommended clients double-tag capabilities
in both experimental and extensions fields. The helper functions remain
as they're useful for checking capability in either location.
* refactor(server): simplify to only getUiCapability, remove hasUiSupport
- Remove hasUiSupport function (use getUiCapability directly)
- Remove double-tagging logic (only check extensions field)
- Add ClientCapabilitiesWithExtensions type using SDK's ClientCapabilities
- Update spec to use getUiCapability
- Simplify tests
* fix: update @see link to getUiCapability
* refactor(server): inline ClientCapabilitiesWithExtensions type in getUiCapability
* refactor: move McpUiClientCapabilities to spec.types.ts
Migrate JSDoc and markdown documentation from `{@includeCode ./file#region}`
tags to inline code fences with `source="./file#region"` attributes.
Code examples are now visible directly in source files while remaining
type-checked via their `.examples.ts` source files.
Add `scripts/sync-snippets.ts` to extract code from `//#region` blocks
and sync it into labeled fences. Run with `npm run sync:snippets`.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
* docs: standardize UI terminology to use "view" consistently
Replaces "widget" and "Guest UI" terminology with "view" across
the codebase as decided in the community survey.
This change updates:
- Specification document
- SDK source code and JSDoc comments
- Example servers and documentation
- Plugin documentation and skills
Closes#71
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Add explicit backtick-wrapped display text to all `{@link}` tags for
monospace rendering in TypeDoc output. This improves readability by:
- Using monospace font for code references (types, methods, functions)
- Stripping module prefixes from display text (e.g., `app!App.connect`
displays as `App.connect`)
Updated files across the SDK including `App`, `AppBridge`,
`PostMessageTransport`, React hooks, server helpers, types, and
documentation.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Add new pattern showing how to combine `updateModelContext()` with
`sendMessage()` when data exceeds message size limits. The example
demonstrates offloading a large transcript to model context first,
then sending a brief trigger message.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Documents `updateModelContext` for keeping the model informed about user
interactions. The example shows a shopping cart use case with YAML frontmatter
for structured, parseable context.
Also refines the `updateModelContext` JSDoc to clarify the difference from
`sendMessage` and removes the `structuredContent` example.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Adds JSDoc example `App_updateModelContext_reportError` showing how to
report runtime errors (e.g., microphone permission denied) back to the
model using `updateModelContext`.
Updates patterns.md with clearer framing:
- Server-side (tool handler): return `{ isError: true, ... }`
- Client-side (app): use `updateModelContext` for runtime errors
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
- Expand `App_ontoolinputpartial_progressiveRendering` example in
`app.examples.ts` to show full state management pattern with
`toolInputs` and `toolInputsPartial` variables
- Add healed JSON caveat to `ontoolinputpartial` JSDoc in `app.ts`
- Update `patterns.md` to reference the expanded example and document
the streaming preview pattern
- Remove empty `lowerPerceivedLatency` placeholder from `patterns.tsx`
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Add `App_onhostcontextchanged_respondToDisplayMode` example showing how to
listen for display mode changes and update UI with `classList.toggle()`.
Update `App_requestDisplayMode_fullscreen` to `App_requestDisplayMode_toggle`
to show the common toggle pattern checking `availableDisplayModes` first.
Refactor full examples (pdf-server, shadertoy-server) to use
`classList.toggle(class, condition)` instead of add/remove branches.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Merge the separate "Support native host styling using CSS variables" and
"Reacting to light/dark theme changes" sections into a single "Matching
host styling (CSS variables, theme, and fonts)" pattern. This provides
clearer guidance by covering all three concerns together.
- Rename `docs/patterns.ts` to `docs/patterns.tsx` for JSX support
- Add `hostStylingVanillaJs` and `hostStylingReact` consolidated examples
- Enhance `applyHostFonts_fromHostContext` to apply initial fonts after
`connect()`, not just on context change
- Add CSS usage examples to `applyHostStyleVariables()` JSDoc
- Update font example to use `var(--font-sans, system-ui, sans-serif)`
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Reference existing JSDoc examples instead of maintaining a separate one in
`docs/patterns.ts`:
- Vanilla JS: `applyDocumentTheme_fromHostContext` from `styles.examples.ts`
- React: `useDocumentTheme_conditionalRender` for reactive theme reading
Expand `applyDocumentTheme_fromHostContext` example to show both the
`onhostcontextchanged` handler and initial theme application after `connect()`.
Note in the docs that `useHostStyles()` applies theme automatically, so React
apps don't need additional setup unless they want to read the theme reactively
for conditional rendering.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
References existing type-checked examples instead of a stub:
- Vanilla JS: `applyHostStyleVariables_fromHostContext` from `src/styles.examples.ts`
- React: `useHostStyles_basicUsage` from `src/react/useHostStyles.examples.tsx`
Expanded `applyHostStyleVariables_fromHostContext` to show the full pattern:
using CSS variables in styles, applying on `onhostcontextchanged`, and
applying initial styles after `connect()`.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Document the `_meta.ui.visibility: ["app"]` feature in `docs/patterns.md`
by referencing the existing type-checked example from
`src/server/index.examples.ts#registerAppTool_toolVisibility`.
- Fix typo: `["apps"]` → `["app"]` (singular)
- Remove placeholder function from `docs/patterns.ts`
- Expand description to explain use cases
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Follow-up to the examples extraction: pass dependencies as function
parameters instead of using global stub declarations, rename region
names to match method names (e.g., `AppBridge_guestCapabilities_*` →
`AppBridge_getAppCapabilities_*`), and simplify examples using optional
chaining.
Also clarifies `RESOURCE_URI_META_KEY` documentation to indicate it's
for tool definition metadata (from `tools/list`), not tool result
metadata, and removes the redundant `setNotificationHandler` example
in favor of the simpler event setter approach.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Extract inline code examples from JSDoc comments into companion
`.examples.ts`/`.examples.tsx` files. Examples are now:
- Type-checked by wrapping them in functions
- Referenced via `{@includeCode ./file.examples.ts#regionName}` tags
- Organized using `//#region` and `//#endregion` markers
This keeps the main source files cleaner while ensuring examples
compile correctly. Updated TypeDoc config with `exampleTag: false`
to support title text on `@example` tags.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Adds a new skill (`plugins/mcp-apps/skills/migrate-oai-app/SKILL.md`)
that guides developers through migrating OpenAI Apps SDK applications
to the MCP Apps SDK. Includes API mapping tables, CSP configuration
guidance, and a "Before Finishing" checklist.
Also fixes the `registerAppResource()` JSDoc example in `src/server/index.ts`
to show CSP configuration in the correct location (on the content item,
not the resource config).
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
