Add FastMCPApp — a Provider for composable MCP applications

.github/workflows/marvin-comment-on-issue.yml

@@ -36,11 +36,6 @@ jobs:
       - name: Install dependencies
         run: uv sync --python 3.12
 
-      - name: Run prek
-        uses: j178/prek-action@v1
-        env:
-          SKIP: no-commit-to-branch
-
       - name: Generate Marvin App token
         id: marvin-token
         uses: actions/create-github-app-token@v2

.github/workflows/marvin-comment-on-pr.yml

@@ -38,11 +38,6 @@ jobs:
       - name: Install dependencies
         run: uv sync --python 3.12
 
-      - name: Run prek
-        uses: j178/prek-action@v1
-        env:
-          SKIP: no-commit-to-branch
-
       - name: Generate Marvin App token
         id: marvin-token
         uses: actions/create-github-app-token@v2

examples/apps/contacts/contacts_server.py

@@ -0,0 +1,152 @@
+"""Contact manager — a FastMCPApp example with forms and callable tool references.
+
+Demonstrates the full FastMCPApp stack:
+- @app.ui() entry point that the model calls to open the app
+- @app.tool() backend tools that the UI calls via CallTool
+- CallTool(fn) with function references (not strings) that resolve to global keys
+- Form.from_model() for auto-generated Pydantic model forms
+- Manual form construction with the context-manager pattern
+
+Usage:
+    uv run python contacts_server.py               # HTTP (default)
+    uv run python contacts_server.py --stdio        # stdio for MCP clients
+"""
+
+from __future__ import annotations
+
+from typing import Literal
+
+from prefab_ui.actions import SetState, ShowToast
+from prefab_ui.actions.mcp import CallTool
+from prefab_ui.app import PrefabApp
+from prefab_ui.components import (
+    Badge,
+    Button,
+    Column,
+    ForEach,
+    Form,
+    Heading,
+    Input,
+    Muted,
+    Row,
+    Separator,
+    Text,
+)
+from prefab_ui.rx import RESULT
+from pydantic import BaseModel, Field
+
+from fastmcp import FastMCP, FastMCPApp
+
+# ---------------------------------------------------------------------------
+# Data
+# ---------------------------------------------------------------------------
+
+_contacts: list[dict] = [
+    {
+        "name": "Arthur Dent",
+        "email": "arthur@earth.com",
+        "category": "Customer",
+        "notes": "",
+    },
+    {
+        "name": "Ford Prefect",
+        "email": "ford@betelgeuse.org",
+        "category": "Partner",
+        "notes": "Researcher",
+    },
+]
+
+
+# ---------------------------------------------------------------------------
+# Pydantic model for auto-generated forms
+# ---------------------------------------------------------------------------
+
+
+class ContactModel(BaseModel):
+    name: str = Field(title="Full Name", min_length=1)
+    email: str = Field(title="Email")
+    category: Literal["Customer", "Vendor", "Partner", "Other"] = "Other"
+    notes: str = Field(
+        default="",
+        title="Notes",
+        json_schema_extra={"ui": {"type": "textarea"}},
+    )
+
+
+# ---------------------------------------------------------------------------
+# App
+# ---------------------------------------------------------------------------
+
+app = FastMCPApp("Contacts")
+
+
+@app.tool()
+def save_contact(data: ContactModel) -> list[dict]:
+    """Save a new contact and return the updated list."""
+    _contacts.append(data.model_dump())
+    return list(_contacts)
+
+
+@app.tool()
+def search_contacts(query: str) -> list[dict]:
+    """Filter contacts by name or email."""
+    q = query.lower()
+    return [c for c in _contacts if q in c["name"].lower() or q in c["email"].lower()]
+
+
+@app.tool(model=True)
+def list_contacts() -> list[dict]:
+    """Return all contacts. Visible to both the model and the UI."""
+    return list(_contacts)
+
+
+@app.ui()
+def contact_manager() -> PrefabApp:
+    """Open the contact manager. The model calls this to launch the app."""
+    with Column(gap=6, css_class="p-6") as view:
+        Heading("Contacts")
+
+        with ForEach("contacts") as contact:
+            with Row(gap=2, align="center"):
+                Text(contact.name, css_class="font-medium")
+                Muted(contact.email)
+                Badge(contact.category)
+
+        Separator()
+
+        Heading("Add Contact", level=3)
+        Form.from_model(
+            ContactModel,
+            on_submit=CallTool(
+                save_contact,
+                on_success=[
+                    SetState("contacts", RESULT),
+                    ShowToast("Contact saved!", variant="success"),
+                ],
+                on_error=ShowToast("{{ $error }}", variant="error"),
+            ),
+        )
+
+        Separator()
+
+        Heading("Search", level=3)
+        with Form(
+            on_submit=CallTool(
+                search_contacts,
+                arguments={"query": "{{ query }}"},
+                on_success=SetState("contacts", RESULT),
+            )
+        ):
+            Input(name="query", placeholder="Search by name or email...")
+            Button("Search")
+
+    return PrefabApp(
+        view=view,
+        state={"contacts": list(_contacts)},
+    )
+
+
+mcp = FastMCP("Contacts Server", providers=[app])
+
+if __name__ == "__main__":
+    mcp.run(transport="http")

pyproject.toml

@@ -53,7 +53,7 @@ classifiers = [
 
 [project.optional-dependencies]
 anthropic = ["anthropic>=0.40.0"]
-apps = ["prefab-ui>=0.6.0"]
+apps = ["prefab-ui>=0.11.0"]
 azure = ["azure-identity>=1.16.0"]
 code-mode = ["pydantic-monty>=0.0.7"]
 gemini = ["google-genai>=1.18.0"]

src/fastmcp/__init__.py

@@ -10,6 +10,7 @@
 
 if TYPE_CHECKING:
     from fastmcp.client import Client as Client
+    from fastmcp.server.app import FastMCPApp as FastMCPApp
 
 settings = Settings()
 if settings.log_enabled:
@@ -40,6 +41,10 @@ def __getattr__(name: str) -> object:
         from fastmcp.client import Client
 
         return Client
+    if name == "FastMCPApp":
+        from fastmcp.server.app import FastMCPApp
+
+        return FastMCPApp
     if name == "client":
         return importlib.import_module("fastmcp.client")
     raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
@@ -49,5 +54,6 @@ def __getattr__(name: str) -> object:
     "Client",
     "Context",
     "FastMCP",
+    "FastMCPApp",
     "settings",
 ]