URL: https://gofastmcp.com/servers/providers/filesystem
Title: Filesystem Provider - FastMCP

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Why Filesystem Discovery
Quick Start
Decorators
@tool
@resource
@prompt
Directory Structure
Discovery Rules
Package Imports
Reload Mode
Error Handling
Example Project
MCP Providers
Filesystem Provider
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Automatic component discovery from Python files
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New in version
3.0.0
FileSystemProvider
scans a directory for Python files and automatically registers functions decorated with
@tool
,
@resource
, or
@prompt
. This enables a file-based organization pattern similar to Next.js routing, where your project structure becomes your component registry.
​
Why Filesystem Discovery
Traditional FastMCP servers require coordination between files. Either your tool files import the server to call
@server.tool()
, or your server file imports all the tool modules. Both approaches create coupling that some developers prefer to avoid.
FileSystemProvider
eliminates this coordination. Each file is self-contained—it uses standalone decorators (
@tool
,
@resource
,
@prompt
) that don’t require access to a server instance. The provider discovers these files at startup, so you can add new tools without modifying your server file.
This is a convention some teams prefer, not necessarily better for all projects. The tradeoffs:
No coordination
: Files don’t import the server; server doesn’t import files
Predictable naming
: Function names become component names (unless overridden)
Development mode
: Optionally re-scan files on every request for rapid iteration
​
Quick Start
Create a provider pointing to your components directory, then pass it to your server. Use
Path(__file__).parent
to make the path relative to your server file.
from
pathlib
import
Path
from
fastmcp
import
FastMCP
from
fastmcp
.
server
.
providers
import
FileSystemProvider
mcp
=
FastMCP
(
"
MyServer
"
,
providers
=[
FileSystemProvider
(
Path
(
__file__
).
parent
/
"
components
"
)])
In your
components/
directory, create Python files with decorated functions.
# components/tools/greet.py
from
fastmcp
.
tools
import
tool
@
tool
def
greet
(
name
:
str
)
->
str
:
"""
Greet someone by name.
"""
return
f
"Hello,
{
name
}
!"
When the server starts,
FileSystemProvider
scans the directory, imports all Python files, and registers any decorated functions it finds.
​
Decorators
FastMCP provides standalone decorators that mark functions for discovery:
@tool
from
fastmcp.tools
,
@resource
from
fastmcp.resources
, and
@prompt
from
fastmcp.prompts
. These support the full syntax of server-bound decorators—all the same parameters work identically.
​
@tool
Mark a function as a tool. The function name becomes the tool name by default.
from
fastmcp
.
tools
import
tool
@
tool
def
calculate_sum
(
a
:
float
,
b
:
float
)
->
float
:
"""
Add two numbers together.
"""
return
a
+
b
Customize the tool with optional parameters.
from
fastmcp
.
tools
import
tool
@
tool
(
name
=
"
add-numbers
"
,
description
=
"
Add two numbers together.
"
,
tags
={
"
math
"
,
"
arithmetic
"
},
)
def
add
(
a
:
float
,
b
:
float
)
->
float
:
return
a
+
b
The decorator supports all standard tool options:
name
,
title
,
description
,
icons
,
tags
,
output_schema
,
annotations
, and
meta
.
​
@resource
Mark a function as a resource. Unlike
@tool
, the
@resource
decorator requires a URI argument.
from
fastmcp
.
resources
import
resource
@
resource
(
"
config://app
"
)
def
get_app_config
()
->
str
:
"""
Get application configuration.
"""
return
'
{"version": "1.0"}
'
URIs with template parameters create resource templates. The provider automatically detects whether to register a static resource or a template based on whether the URI contains
{parameters}
or the function has arguments.
from
fastmcp
.
resources
import
resource
@
resource
(
"
users://
{user_id}
/profile
"
)
def
get_user_profile
(
user_id
:
str
)
->
str
:
"""
Get a user's profile by ID.
"""
return
f
'
{{
"id": "
{
user_id
}
", "name": "User"
}}
'
The decorator supports:
uri
(required),
name
,
title
,
description
,
icons
,
mime_type
,
tags
,
annotations
, and
meta
.
​
@prompt
Mark a function as a prompt template.
from
fastmcp
.
prompts
import
prompt
@
prompt
def
code_review
(
code
:
str
,
language
:
str
=
"
python
"
)
->
str
:
"""
Generate a code review prompt.
"""
return
f
"Please review this
{
language
}
code:
\n\n
```
{
language
}
\n
{
code
}
\n
```"
from
fastmcp
.
prompts
import
prompt
@
prompt
(
name
=
"
explain-concept
"
,
tags
={
"
education
"
})
def
explain
(
topic
:
str
)
->
str
:
"""
Generate an explanation prompt.
"""
return
f
"Explain
{
topic
}
using clear examples and analogies."
The decorator supports:
name
,
title
,
description
,
icons
,
tags
, and
meta
.
​
Directory Structure
The directory structure is purely organizational. The provider recursively scans all
.py
files regardless of which subdirectory they’re in. Subdirectories like
tools/
,
resources/
, and
prompts/
are optional conventions that help you organize code.
components/
├── tools/
│ ├── greeting.py # @tool functions
│ └── calculator.py # @tool functions
├── resources/
│ └── config.py # @resource functions
└── prompts/
└── assistant.py # @prompt functions
You can also put all components in a single file or organize by feature rather than type.
components/
├── user_management.py # @tool, @resource, @prompt for users
├── billing.py # @tool, @resource for billing
└── analytics.py # @tool for analytics
​
Discovery Rules
The provider follows these rules when scanning:
Rule
Behavior
File extensions
Only
.py
files are scanned
__init__.py
Skipped (used for package structure, not components)
__pycache__
Skipped
Private functions
Functions starting with
_
are ignored, even if decorated
No decorators
Files without
@tool
,
@resource
, or
@prompt
are silently skipped
Multiple components
A single file can contain any number of decorated functions
​
Package Imports
If your directory contains an
__init__.py
file, the provider imports files as proper Python package members. This means relative imports work correctly within your components directory.
# components/__init__.py exists
# components/tools/greeting.py
from
..
helpers
import
format_name
# Relative imports work
@
tool
def
greet
(
name
:
str
)
->
str
:
return
f
"Hello,
{
format_name
(
name
)
}
!"
Without
__init__.py
, files are imported directly using
importlib.util.spec_from_file_location
.
​
Reload Mode
During development, you may want changes to component files to take effect without restarting the server. Enable reload mode to re-scan the directory on every request.
from
pathlib
import
Path
from
fastmcp
.
server
.
providers
import
FileSystemProvider
provider
=
FileSystemProvider
(
Path
(
__file__
).
parent
/
"
components
"
,
reload
=
True
)
With
reload=True
, the provider:
Re-discovers all Python files on each request
Re-imports modules that have changed
Updates the component registry with any new, modified, or removed components
Reload mode adds overhead to every request. Use it only during development, not in production.
​
Error Handling
When a file fails to import (syntax error, missing dependency, etc.), the provider logs a warning and continues scanning other files. Failed imports don’t prevent the server from starting.
WARNING - Failed to import /path/to/broken.py: No module named 'missing_dep'
The provider tracks which files have failed and only re-logs warnings when the file’s modification time changes. This prevents log spam when a broken file is repeatedly scanned in reload mode.
​
Example Project
A complete example is available in the repository at
examples/filesystem-provider/
. The structure demonstrates the recommended organization.
examples/filesystem-provider/
├── server.py # Server entry point
└── components/
├── tools/
│ ├── greeting.py # greet, farewell tools
│ └── calculator.py # add, multiply tools
├── resources/
│ └── config.py # Static and templated resources
└── prompts/
└── assistant.py # code_review, explain prompts
The server entry point is minimal.
from
pathlib
import
Path
from
fastmcp
import
FastMCP
from
fastmcp
.
server
.
providers
import
FileSystemProvider
provider
=
FileSystemProvider
(
root
=
Path
(
__file__
).
parent
/
"
components
"
,
reload
=
True
,
)
mcp
=
FastMCP
(
"
FilesystemDemo
"
,
providers
=[
provider
])
Run with
fastmcp run examples/filesystem-provider/server.py
or inspect with
fastmcp inspect examples/filesystem-provider/server.py
.
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