fastmcp/docs/development/upgrade-guide.mdx

---
title: Upgrade Guide
sidebarTitle: Upgrade Guide
description: Migration instructions for upgrading between FastMCP versions
icon: up
tag: NEW
---

This guide provides migration instructions for breaking changes and major updates when upgrading between FastMCP versions.

## v3.0.0

### WSTransport Removed

The deprecated `WSTransport` client transport has been removed. Use `StreamableHttpTransport` instead.

### Decorators Return Functions

<Warning>
**Breaking Change:** Decorators now return your original function instead of a component object. Code that treats the decorated function as a `FunctionTool`, `FunctionResource`, or `FunctionPrompt` will break.
</Warning>

Decorators (`@tool`, `@resource`, `@prompt`) now return the original function instead of transforming it into a component object:

<CodeGroup>
```python Before
@mcp.tool
def greet(name: str) -> str:
    return f"Hello, {name}!"

isinstance(greet, FunctionTool)  # True
greet.name                       # "greet"
```

```python After
@mcp.tool
def greet(name: str) -> str:
    return f"Hello, {name}!"

isinstance(greet, FunctionTool)  # False - it's your function now
greet("World")                   # "Hello, World!" - still callable
```
</CodeGroup>

**Why this changed:** Functions staying as functions means they're directly callable for testing, work naturally with instance methods, and match how Flask/FastAPI decorators behave.

**For v2 compatibility:**

```python
import fastmcp
fastmcp.settings.decorator_mode = "object"
```

Or set the environment variable `FASTMCP_DECORATOR_MODE=object`.

### Provider Architecture

FastMCP v3 introduces a unified provider architecture for sourcing components. All tools, resources, and prompts now flow through providers:

- **LocalProvider** stores decorator-registered components (`@mcp.tool`, etc.)
- **FastMCPProvider** wraps another FastMCP server for composition
- **ProxyProvider** connects to remote MCP servers
- **Transforms** modify components as they flow through using a middleware `call_next` pattern

See [Providers](/servers/providers/overview) and [Transforms](/servers/providers/transforms) for documentation.

### Tool Transformation API

`FastMCP.add_tool_transformation()` and the `tool_transformations` constructor parameter are deprecated. Use `add_transform()` with `ToolTransform` instead:

<CodeGroup>
```python Before
mcp = FastMCP("server", tool_transformations={
    "verbose_name": ToolTransformConfig(name="short")
})
mcp.add_tool_transformation("verbose_name", ToolTransformConfig(name="short"))
```

```python After
from fastmcp.server.transforms import ToolTransform
from fastmcp.tools.tool_transform import ToolTransformConfig

mcp = FastMCP("server")
mcp.add_transform(ToolTransform({
    "verbose_name": ToolTransformConfig(name="short")
}))
```
</CodeGroup>

`remove_tool_transformation()` is deprecated with no replacement - transforms are immutable once added. Use `server.disable(keys=[...])` to hide tools dynamically.

### FastMCP.as_proxy() Deprecated

The `FastMCP.as_proxy()` classmethod is deprecated. Use the `create_proxy()` function instead ([#2829](https://github.com/jlowin/fastmcp/pull/2829)):

<CodeGroup>
```python Before
proxy = FastMCP.as_proxy("http://example.com/mcp")
```

```python After
from fastmcp.server import create_proxy

proxy = create_proxy("http://example.com/mcp")
```
</CodeGroup>

`as_proxy()` continues to work but forwards to `create_proxy()`.

### Mount Namespace Parameter

The `prefix` parameter for `mount()` has been renamed to `namespace`:

<CodeGroup>
```python Before
main.mount(subserver, prefix="api")
```

```python After
main.mount(subserver, namespace="api")
```
</CodeGroup>

### Component Enable/Disable

The `enabled` field and `enable()`/`disable()` methods have been removed from component objects. Use server or provider methods instead:

<CodeGroup>
```python Before
tool = await server.get_tool("my_tool")
tool.disable()
tool.enable()
```

```python After
server.disable(keys=["tool:my_tool"])
server.enable(keys=["tool:my_tool"])
```
</CodeGroup>

Components describe capabilities; servers and providers control availability. This ensures mutations work correctly even when components pass through transforming providers.

**Allowlist mode:**

Use `only=True` to restrict visibility to specific components:

```python
# Show ONLY tools with "public" tag
server.enable(tags={"public"}, only=True)
```

**`FastMCP(include_tags=..., exclude_tags=...)` deprecated:**

These init parameters emit deprecation warnings. Use the new methods instead:

```python
# Before
mcp = FastMCP("server", exclude_tags={"internal"})

# After
mcp = FastMCP("server")
mcp.disable(tags={"internal"})
```

### Component Lookup Method Parameter Names

The server lookup methods now use semantic parameter names instead of generic `key`:

- `FastMCP.get_tool(name=...)` (was `key`)
- `FastMCP.get_resource(uri=...)` (was `key`)
- `FastMCP.get_resource_template(uri=...)` (was `key`)
- `FastMCP.get_prompt(name=...)` (was `key`)

If you were passing arguments positionally, no change is needed. If you were using keyword arguments:

<CodeGroup>
```python Before
tool = await mcp.get_tool(key="my_tool")
```

```python After
tool = await mcp.get_tool(name="my_tool")
```
</CodeGroup>

### Component Listing Methods Return Lists

The `get_tools()`, `get_resources()`, `get_prompts()`, and `get_resource_templates()` methods now return lists instead of dicts:

<CodeGroup>
```python Before
tools = await server.get_tools()
if "my_tool" in tools:
    tool = tools["my_tool"]
```

```python After
tools = await server.get_tools()
tool = next((t for t in tools if t.name == "my_tool"), None)
```
</CodeGroup>

The dict key was redundant since components already have `.name` or `.uri` attributes. Use list comprehensions or `next()` for lookups.

### Prompt Return Types

Prompt functions now use `Message` instead of `mcp.types.PromptMessage`. The `Message` class provides auto-serialization and a simpler API:

<CodeGroup>
```python Before
from mcp.types import PromptMessage, TextContent

@mcp.prompt
def my_prompt() -> PromptMessage:
    return PromptMessage(
        role="user",
        content=TextContent(type="text", text="Hello")
    )
```

```python After
from fastmcp.prompts import Message

@mcp.prompt
def my_prompt() -> Message:
    return Message("Hello")  # role defaults to "user"
```
</CodeGroup>

**Key changes:**

- Use `Message(content, role="user")` instead of `PromptMessage(role=..., content=TextContent(...))`
- `Message` auto-serializes dicts, lists, and Pydantic models to JSON
- `PromptResult` now accepts `str | list[Message]` (no single `Message`)
- Returning `mcp.types.PromptMessage` directly is no longer supported

See [Prompts documentation](/servers/prompts#return-values) for full details.

### Tool Serializer Deprecated

The `tool_serializer` parameter on `FastMCP` is deprecated. Return `ToolResult` from your tools for explicit control over serialization. See [Custom Serialization](/servers/tools#custom-serialization) for examples.

### Auth Provider Automatic Environment Variable Loading Removed

Auth providers no longer automatically read configuration from environment variables. You can still use environment variables, but you must read them yourself:

<CodeGroup>
```python Before
# Relied on FASTMCP_SERVER_AUTH_GITHUB_CLIENT_ID, etc.
auth = GitHubProvider()
```

```python After
import os

auth = GitHubProvider(
    client_id=os.environ["GITHUB_CLIENT_ID"],
    client_secret=os.environ["GITHUB_CLIENT_SECRET"],
    base_url=os.environ["GITHUB_BASE_URL"],
)
```
</CodeGroup>

This applies to all auth providers: `GitHubProvider`, `GoogleProvider`, `AzureProvider`, `Auth0Provider`, `AWSProvider`, `WorkOSProvider`, `DescopeProvider`, `DiscordProvider`, `ScalekitProvider`, `SupabaseProvider`, `OCIProvider`, `JWTVerifier`, and `IntrospectionVerifier`.

The `FastMCPSettings` class has also been simplified - it no longer includes auth-related settings that were previously loaded from environment variables.

### Server Banner Environment Variable Renamed

The environment variable for controlling the server banner has been renamed:

- **Before:** `FASTMCP_SHOW_CLI_BANNER`
- **After:** `FASTMCP_SHOW_SERVER_BANNER`

This change reflects that the setting now applies to all server startup methods, not just the CLI. The banner is now suppressed when running `python server.py` directly, not just when using `fastmcp run`.

### Context State Methods Are Async

<Warning>
**Breaking Change:** `ctx.set_state()` and `ctx.get_state()` are now async methods. Synchronous calls will fail.
</Warning>

Context state has changed from request-scoped to session-scoped, persisting across multiple tool calls within the same MCP session. The methods are now async because they interact with a pluggable storage backend.

<CodeGroup>
```python Before
@mcp.tool
def my_tool(ctx: Context) -> str:
    ctx.set_state("key", "value")
    value = ctx.get_state("key")
    return value
```

```python After
@mcp.tool
async def my_tool(ctx: Context) -> str:
    await ctx.set_state("key", "value")
    value = await ctx.get_state("key")
    return value
```
</CodeGroup>

**What changed:**
- State now persists across requests within a session (not just within a single request)
- Different clients have isolated state (keyed by session ID)
- State expires after 1 day to prevent unbounded memory growth
- New method: `await ctx.delete_state(key)`

**Custom storage backends:**

By default, state uses an in-memory store. For distributed deployments, provide a custom backend:

```python
from key_value.aio.stores.redis import RedisStore

mcp = FastMCP("server", session_state_store=RedisStore(...))
```

See [Session State](/servers/context#session-state) for full documentation.

## v2.14.0

### OpenAPI Parser Promotion

The experimental OpenAPI parser is now the standard implementation. The legacy parser has been removed.

**If you were using the legacy parser:** No code changes required. The new parser is a drop-in replacement with improved architecture.

**If you were using the experimental parser:** Update your imports from the experimental module to the standard location:

<CodeGroup>
```python Before
from fastmcp.experimental.server.openapi import FastMCPOpenAPI, RouteMap, MCPType
```

```python After
from fastmcp.server.openapi import FastMCPOpenAPI, RouteMap, MCPType
```
</CodeGroup>

The experimental imports will continue working temporarily but will show deprecation warnings. The `FASTMCP_EXPERIMENTAL_ENABLE_NEW_OPENAPI_PARSER` environment variable is no longer needed and can be removed.

### Deprecated Features Removed

The following deprecated features have been removed in v2.14.0:

**BearerAuthProvider** (deprecated in v2.11):
<CodeGroup>
```python Before
from fastmcp.server.auth.providers.bearer import BearerAuthProvider
```

```python After
from fastmcp.server.auth.providers.jwt import JWTVerifier
```
</CodeGroup>

**Context.get_http_request()** (deprecated in v2.2.11):
<CodeGroup>
```python Before
request = context.get_http_request()
```

```python After
from fastmcp.server.dependencies import get_http_request
request = get_http_request()
```
</CodeGroup>

**Top-level Image import** (deprecated in v2.8.1):
<CodeGroup>
```python Before
from fastmcp import Image
```

```python After
from fastmcp.utilities.types import Image
```
</CodeGroup>

**FastMCP dependencies parameter** (deprecated in v2.11.4):
<CodeGroup>
```python Before
mcp = FastMCP("server", dependencies=["requests", "pandas"])
```

```json After
{
  "environment": {
    "dependencies": ["requests", "pandas"]
  }
}
```
</CodeGroup>

**Legacy resource prefix format**: The `resource_prefix_format` parameter and "protocol" format have been removed. Only the "path" format is supported (this was already the default).

**FastMCPProxy client parameter**:
<CodeGroup>
```python Before
proxy = FastMCPProxy(client=my_client)
```

```python After
proxy = FastMCPProxy(client_factory=lambda: my_client)
```
</CodeGroup>

**output_schema=False**:
<CodeGroup>
```python Before
@mcp.tool(output_schema=False)
def my_tool() -> str:
    return "result"
```

```python After
@mcp.tool(output_schema=None)
def my_tool() -> str:
    return "result"
```
</CodeGroup>

## v2.13.0

### OAuth Token Key Management

The OAuth proxy now issues its own JWT tokens to clients instead of forwarding upstream provider tokens. This improves security by maintaining proper token audience boundaries.

**What changed:**

The OAuth proxy now implements a token factory pattern - it receives tokens from your OAuth provider (GitHub, Google, etc.), encrypts and stores them, then issues its own FastMCP JWT tokens to clients. This requires cryptographic keys for JWT signing and token encryption.

**Default behavior (development):**

By default, FastMCP automatically manages keys based on your platform:
- **Mac/Windows**: Keys are auto-managed via system keyring, surviving server restarts with zero configuration. Suitable **only** for development and local testing.
- **Linux**: Keys are ephemeral (random salt at startup, regenerated on each restart).

This works fine for development and testing where re-authentication after restart is acceptable.

**For production:**

Production deployments must provide explicit keys and use persistent storage. Add these three things:

```python
auth = GitHubProvider(
    client_id=os.environ["GITHUB_CLIENT_ID"],
    client_secret=os.environ["GITHUB_CLIENT_SECRET"],
    base_url="https://your-server.com",

    # Explicit keys (required for production)
    jwt_signing_key=os.environ["JWT_SIGNING_KEY"],

    # Persistent network storage (required for production)
    client_storage=RedisStore(host="redis.example.com", port=6379)
)
```

**More information:**
- [OAuth Token Security](/deployment/http#oauth-token-security) - Complete production setup guide
- [Key and Storage Management](/servers/auth/oauth-proxy#key-and-storage-management) - Detailed explanation of defaults and production requirements
- [OAuth Proxy Parameters](/servers/auth/oauth-proxy#configuration-parameters) - Parameter documentation