Sourced from fastmcp's releases.

v3.2.0: Show Don't Tool

FastMCP 3.2 is the Apps release. The 3.0 architecture gave you providers and transforms; 3.1 shipped Code Mode for tool discovery. 3.2 puts a face on it: your tools can now return interactive UIs — charts, dashboards, forms, maps — rendered right inside the conversation.

FastMCPApp

FastMCPApp is a new provider class for building interactive applications inside MCP. It separates the tools the LLM sees (@app.ui()) from the backend tools the UI calls (@app.tool()), manages visibility automatically, and gives tool references stable identifiers that survive namespace transforms and server composition — without requiring host cooperation.

from fastmcp import FastMCP, FastMCPApp
from prefab_ui.actions.mcp import CallTool
from prefab_ui.components import Column, Form, Input, Button, ForEach, Text
app = FastMCPApp("Contacts")
@​app.tool()
def save_contact(name: str, email: str) -> list[dict]:
db.append({"name": name, "email": email})
return list(db)
@​app.ui()
def contact_manager() -> PrefabApp:
with PrefabApp(state={"contacts": list(db)}) as view:
with Column(gap=4):
ForEach("contacts", lambda c: Text(c.name))
with Form(on_submit=CallTool("save_contact")):
Input(name="name", required=True)
Input(name="email", required=True)
Button("Save")
return view
mcp = FastMCP("Server", providers=[app])

The UI is built with Prefab, a Python component library that compiles to interactive UIs. You write Python; the user sees charts, tables, forms, and dashboards. FastMCP handles the MCP Apps protocol machinery — renderer resources, CSP configuration, structured content serialization — so you don't have to.

For simpler cases where you just want to visualize data without server interaction, set app=True on any tool and return Prefab components directly:

@mcp.tool(app=True)
def revenue_chart(year: int) -> PrefabApp:
    with PrefabApp() as app:
        BarChart(data=revenue_data, series=[ChartSeries(data_key="revenue")])
    return app

Built-in Providers

Five ready-made providers you add with a single add_provider() call:

• FileUpload — drag-and-drop file upload with session-scoped storage

... (truncated)

Sourced from fastmcp's changelog.

---

title: "Changelog" icon: "list-check" rss: true tag: NEW

v3.1.1: 'Tis But a Patch

Pins pydantic-monty below 0.0.8 to fix a breaking change in Monty that affects code mode. Monty 0.0.8 removed the external_functions constructor parameter, causing MontySandboxProvider to fail. This patch caps the version so existing installs work correctly.

Fixes 🐞

• Pin pydantic-monty below 0.0.8 to fix code mode by @​jlowin in #3497

Full Changelog: v3.1.0...v3.1.1

v3.1.0: Code to Joy

FastMCP 3.1 is the Code Mode release. The 3.0 architecture introduced providers and transforms as the extensibility layer — 3.1 puts that architecture to work, shipping the most requested capability since launch: servers that can find and execute code on behalf of agents, without requiring clients to know what tools exist.

New Features 🎉

• feat: Search transforms for tool discovery by @​jlowin in #3154
• Add experimental CodeMode transform by @​aaazzam in #3297
• Add Prefab Apps integration for MCP tool UIs by @​jlowin in #3316

Enhancements 🔧

• Lazy-load heavy imports to reduce import time by @​jlowin in #3295
• Add http_client parameter to all token verifiers for connection pooling by @​jlowin in #3300
• Add in-memory caching for token introspection results by @​jlowin in #3298
• Add SessionStart hook to install gh CLI in cloud sessions by @​jlowin in #3308
• Fix ty 0.0.19 type errors by @​jlowin in #3310
• Code Mode: Add resource limits to MontySandboxProvider by @​jlowin in #3326
• Accept transforms as FastMCP init kwarg by @​jlowin in #3324
• Split large test files to comply with loq line limit by @​jlowin in #3328
• Add -m/--module flag to fastmcp run and dev inspector by @​dgenio in #3331
• Add search_result_serializer hook and serialize_tools_for_output_markdown by @​MagnusS0 in #3337
• Add MultiAuth for composing multiple token verification sources by @​jlowin in #3335
• Adds PropelAuth as an AuthProvider by @​andrew-propelauth in #3358
• Replace vendored DI with uncalled-for by @​chrisguidry in #3301
• Decompose CodeMode into composable discovery tools by @​jlowin in #3354
• feat(contrib): auto-sync MCPMixin decorators with from_function signatures by @​AnkeshThakur in #3323
• Add Google GenAI Sampling Handler by @​strawgate in #2977
• Add ListTools, search limit, and catalog size annotation to CodeMode by @​jlowin in #3359
• Allow configuring FastMCP transport setting in the same way as other configuration by @​jvdmr in #1796
• Add include_unversioned option to VersionFilter by @​yangbaechu in #3349

... (truncated)

• 665514e Add forward_resource flag to OAuthProxy (#3711)
• f189d1f Bump pydantic-monty to 0.0.9 (#3707)
• 6faa2d6 Remove hardcoded prefab-ui version from pinning warnings (#3708)
• dd8816c chore: Update SDK documentation (#3701)
• d274959 docs: note that custom routes are unauthenticated (#3706)
• 4a54be2 Add examples gallery page (#3705)
• 961dd50 Add interactive map example with geocoding (#3702)
• f01d0c5 Add quiz example app, fix dev server empty string args (#3700)
• 85b7efd chore: Update SDK documentation (#3694)
• 27abe3c Add sales dashboard and live system monitor examples, bump prefab-ui to 0.17 ...
• Additional commits viewable in compare view

You can trigger Dependabot actions by commenting on this PR:

• @dependabot rebase will rebase this PR
• @dependabot recreate will recreate this PR, overwriting any edits that have been made to it
• @dependabot show <dependency name> ignore conditions will show all of the ignore conditions of the specified dependency
• @dependabot ignore this major version will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this minor version will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this dependency will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)
  You can disable automated security fix PRs for this repo from the Security Alerts page.