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Build Anything With a CUSTOM MCP Server - Python Tutorial

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in this video I'm going to show you how

to build a custom MCP server in Python

and connect that to an AI agent this is

going to be very beginner friendly but

it's going to illustrate what an MCP

server actually is and how you make your

own and how you can extend this to do

some really cool stuff now excuse the

shirt i don't usually wear a tank top

when I'm recording videos but it is

extremely hot here so please don't get

too distracted and let's get into the

video all right so first things first if

you don't understand MCP servers yet I

made a video on them that's been doing

really well in the past few days

explaining exactly what they are there's

some diagrams i show you how to connect

it to AI code editors for example like

cursor but the quick gist is that an MCP

server just provides various tools or

resources to something like an AI agent

so that it can utilize additional

context or it can call an API or it can

save a node or connect to a database it

can do things outside of its current

abilities so here I'm going to show you

how to make your own MCP server so that

you can write your own tools that you

provide to AI agents it could be other

AI agents or your own AI agents it

doesn't really matter and MCP servers

are just kind of the new fancy term for

essentially how LLMs and AI tools

communicate with each other okay so

let's get into it here i'll link this

video in the description in case you

want more information now we're going to

be using the MCP Python SDK which makes

this very easy to do and there are a few

setup steps so we're going to be using

UV so first thing you need to do if you

don't have this installed is install UV

this is a package manager that's just

significantly better than pip i'll have

a video coming out about this in a few

days that will talk about it more in

depth but anyways if you're on Windows

you're going to want to copy this first

command into PowerShell it will install

UV for you and if you're on Mac or Linux

you can copy any of these commands and

again install UV now you can install

this using Pi or PIP but I don't

recommend that you do that because it's

going to make it a lot more complicated

later in the video okay beyond that I am

going to suggest that you download

Claude Desktop this is free and it's

going to be one of the easiest ways to

test our MCP server so please just

download this cuz I'm going to show you

how to add your MCP server to Claude

Desktop so you can actually see an LLM

interacting with it and using those

various tools okay so once we have UV

installed we're just going to follow the

instructions here from the readme of the

uh MCP Python SDK and what we need to do

is initialize a new UV project so I'm

going to put this on the right hand side

of my screen and I'm going to open up

the code editor that I'll be using for

this video which is PyCharm now you may

be wondering why am I using PyCharm this

really is just the best IDE to be using

it has tons of tools built in makes it

really easy to work with Python code

view the documentation especially if

you're working with things like servers

or APIs it has a built-in network tabs

you can directly test them there and a

ton of other great features i also do

have a long-term partnership with

PyCharm where I'm able to give you

access to a 3month free extended trial

of their PyCharm Pro subscription you

can get access to that with the details

that are in the description check it out

see if you like it and obviously for

this video you can use anything that you

want but I do recommend PyCharm but the

first step is to just open some kind of

folder in whatever code editor you want

to use okay so I'm using PyCharm and

I've opened a folder called MCP server

tutorial to open that you typically are

going to go to the file menu you're

going to go to open you can make a new

folder or you can open an existing one

and I suggest you just make a new folder

and then open that okay so from here I'm

going to open up my terminal in my

terminal I'm in the current directory

where I want to initialize this project

and because I've already installed UV

and let me just quickly zoom in here so

you guys can actually see this i'm going

to type UV init and then dot when I do

the dot this means initialize a new UV

project in the current directory okay so

we have UVIT dot so that's kind of what

this wanted us to do here and next we

need to install the dependencies and the

dependency is going to be MCP and then

CLI so we're simply going to go here and

say UV add MCP CLI okay that's going to

install it instantly using UV and if we

look here at our directory we should see

a few files we have a uh venv this is

our virtual environment we have main.py

we have this readme we have all of these

things all right so that's installed now

the next step here is going to be to

open this main.py file if you don't have

the file again you can create one uh

don't worry about the interpreter i'm

going to fix that here in 1 second and

then we're going to start writing a

simple MCP server we're going to test it

and then we will adapt this to be

something a little bit more custom all

right all right so to get started here

we can literally just copy the code from

the quick start guide here again I'm

going to link this GitHub in the

description and you can see here that

what we do is we say from

mcp.server.fastmcp we have fastmcp we

create an MCP server we give this a name

in this case it's called demo then we

create a tool and then we have a

resource now I'm going to talk about

what these are in one second but this is

literally all you need in order to get

started with the MCP server and the next

step is to actually install this or use

it from some LLM or some AI tool so

again I literally just copied this from

the quick start but I'm going to show

you now how we install this into Claw

Desktop so we can start testing it and

then we'll change this to a more custom

example now look we have a tool okay we

have a tool that allows us to add two

numbers obviously that's pretty naive

and then we have a greeting okay or a

resource and we can greet someone based

on their name so in order to install

this we can do it manually or we can use

the MCP CLI that we just installed so

I'm going to open up my terminal again

make sure you're in the same directory

of your UV project and what you can type

is uvun and then mcp install and then

the name of your Python file and in this

case it's not server.py it's main.py

because that's what I named the file

okay so I'm going to go with

main.py now when I do that what it

should do is add this configuration to

our Claude desktop i'm going to show you

how we get that configuration and then

how we check if this is working okay so

now that we've done that we're going to

open up Claude now obviously that step

only works if you have Claude desktop

installed you don't need to use Claude

desktop but this is a good demo for this

video so we're going to open this up

here and what we can do if we want to

check the configuration is we can go

here to the three kind of uh what do you

call it bars or the menu we can go to

file and we can go to settings i'll have

my editor zoom in here so you guys can

see this from settings we're going to go

to developer and we're going to go here

to edit config okay now from edit config

it's likely going to open up some

directory for you what you're going to

want to do is open up this claw desktop

configuration file okay so I'm going to

open this up just in Sublime Text but

you can open this in anything that you

want and you're going to see that you

have some command and then you have some

arguments now what this is saying is hey

we're going to use UV the thing that you

just installed we're going to run it

with this MCP CLI and then we're going

to run the command MCP run and then this

server right here now once that's

running within Claude we should actually

be able to see this however there's some

common errors that can occur that I'm

going to show you how to get over so

really this configuration is added and

we should be able to see the MCP server

but the MCP server should show up right

here and we're not seeing it right now

now I ran into a bunch of issues with

this when I was testing and I found a

few potential fixes the first fix is

just to shut down claw desktop

completely so force quit it from your

task manager or your process list and

then reopen it so let's try that and see

if it works if it doesn't I'm going to

show you the alternative solution so I

just opened my task manager here and I'm

just going to shut down Claude desktop

okay so I'm going to end the task and

then I'm just going to wait a second and

I'm going to reopen it okay so we're

going to reopen Claude now we're hoping

that once this loads it's going to spin

up our MCP server and it looks like it

actually did so you see here now that we

have a hammer and that we have I guess

this kind of like plug here where we can

attach something from the MCP now that's

not going to work right now but we can

go to available MCP tools and we can see

that we have this add tool from the

server demo and it says it adds two

numbers so now what I can do is I can

use say something like can you add 1 + 7

and it should go ahead and use this MCP

tool this one right here that's

available okay let's see if it does that

you can see that it says running ad from

demo and we're going to say yes we will

allow this for this chat it's using the

parameter A and B and then it gets the

result which is eight okay this is a

very very simple demo of using the MCP

server but the point is if it doesn't

work restart it now if that's still not

working for you another way to fix this

is to put the absolute path to where UV

is installed now the absolute path for

where UV is installed will depend on

your operating system and how you

installed it but I'm going to show you

how you can find it so you can go to

your terminal and you can type which if

you're on Mac or Linux and then UV when

you do that it should show you the

location of where this was installed and

then what you can do is put the absolute

location to this UV file now in my case

I can also type where UV and notice it's

not showing me where this exists i can

try something like where UV.exe exe and

it's still not showing it to me so what

I had to do is look up the default

installation location and I found that

the location for this was the following

i'm just going to open it up right now

okay so again we'll zoom in here but the

default location on Windows if you

install this with the PowerShell command

is going to be C/ user/ the name of your

user in my case I called mine user kind

of silly but this would be like Tim or

Joe or like whatever your current user

is on Windows and then dot /local and

then /bin inside of here you have the UV

directory so what you could do if this

command wasn't working is you would

change the configuration here to be the

following you would put your directory

you would escape these with two

backslashes because that's just how it

works here in Windows and then you would

/uv.exe so you're pointing directly to

this UV executable so that you can

actually use it again same thing on Mac

you put the absolute location to the UV

executable file it won't be.exe it will

probably just be UV or UV.sh SH or

something along those lines now clearly

I don't need that because this is

working so I will just leave it as UV

and you could add other servers here as

well using the same configuration that

you see like this where essentially what

happens is once Claude boots up it runs

this command runs the server it's then

able to connect to this using the

standard input output protocol we don't

need to talk about that in too much

depth and utilize your tools okay so now

that this is working we are going to

shut down claude again and we're going

to go into our editor and we're actually

going to write a useful MCP server and

to do that we're quickly going to cover

some of the important concepts related

to MCP servers that are here on this

page so what we can do with MCP servers

is we can expose data through resources

so think of like a get endpoint like a

HTTP get endpoint where you're exposing

like a database or some context or a

memory or whatever like just anything

that is essentially retrieving data okay

that's a resource that you can expose

via MCP another thing that you can do is

provide a tool now a tool is something

that typically does something maybe it

goes and scrapes the web or it adds a

new user it performs some operation and

again that's something that you know

these AI agents like to use a lot and

that you can provide with an MCP server

you also can provide a prompt so this is

a reusable template for interacting with

LLMs and I'm going to show you all of

those in this video and how they connect

with Claude so you can see for a

resource you do something like at

mcp.resource okay for a tool you do

mcp.tool and for a prompt you do

atmc.prompt you also can connect images

and context i'm not going to show that

right now uh but that is something that

you can't do okay cool so let's get out

of that let's go back into our editor

and let me show you a real tool that

might actually be useful or at least

demonstrates how you write this out all

right so I just cleared my file here so

we just have some basic code so we're

kind of just starting from scratch and

what I'm going to do is I'm just going

to call this AI sticky notes okay and

the idea is going to be that we're going

to allow the uh AI to kind of take some

notes and store that in some external

storage in this case we'll just use like

a notepad file and this will show us how

we can kind of like read and write and

get resources and utilize tools uh it'll

be interesting enough to at least give

you like the kind of starting template

for building your own MCP so what we're

going to do is we're going to go up here

and we're going to say import OS cuz

we're going to use this in 1 second and

we're going to define a variable called

notes file and we're going to make this

equal to just like

notes.txt okay you know this is going to

be where we are storing the notes that

the MCP server will actually have access

to now we're going to make a function

we're just going to say insure file and

all this is going to do is just make

sure that this file exists before we

start trying to use it so we're going to

say if not

os.path.exists and then the notes file

you can see my autocomplete is taking

over here then what I'm going to do is

I'm going to say with open notes uh file

wf i'll explain this in one second then

I'm going to say f.right Right and I'm

just going to write an empty uh line in

here like an empty string okay you don't

really need to do this but this is what

we're going to do so we're going to say

if not os.path.exists what this is doing

is saying all right does this file exist

if it does not exist then we're going to

use this fancy Python syntax which

essentially will open up a file for us

and make sure there's no errors doing

that this is going to create a new file

because we did this in W mode this means

it will create and override any file

that currently exists and then we just

write nothing into it just so that we

have something happening inside of this

width statement okay so we're going to

run that before we do any operation on

our file just to make sure the file is

indeed there now we're going to make an

MCP tool now to make an MCP tool is

super straightforward all you have to do

is type at MCP tool and then make sure

you close your parenthesis here and this

is what's called a decorator in Python

it's something that essentially modifies

a function you don't need to worry too

much about what that means then what we

can do is we can give the tool a name

and we do that by defining a function

with the name of the tool so in this

case we say define add note okay and now

we've just made a tool called add notes

that our LLM or that our AI agent would

be able to call now for this function

we're going to specify the parameters or

the values that the AI agent would pass

to it so for adding a note we probably

have like a message that we want the AI

agent to pass so we can specify as many

parameters as we want but we need to

make sure that we specify a type for

those parameters so the AI agent knows

how to pass them so we're going to say

message and then colon string and then

we're also going to specify the return

type of this function by using a type

hint in Python so we're going to use a

dash and then the greater than sign and

then string okay now what this

effectively says is hey we have this

function we take in some message this

will be given by the LLM or by the AI

agent it's going to return some string

and then inside of here we can start

writing out the actual function so the

first thing we're going to do is we're

going to say insure file so we're going

to make sure the file does exist then

we're going to say with open and same

thing we're going to open the notes file

we're going to open this in a mode which

stands for append mode which means we're

not going to override it but we're going

to write to the end and then we're going

to say f.right write and we're going to

write the message plus a new line

character this means we will go down to

the next line in the file after we write

the message and then we're just going to

return a string that says note saved

okay so just give the LLM some output

that this actually was successful now at

this point this tool is done if we go

back to Claude and we restart it we'll

be able to start using this tool and

adding a new note but there's one more

step that you don't want to forget now

that step is adding what's called a dock

string okay and you can see in PyCharm

here it automatically populated it again

another advantage of using something

like PyCharm now a dock string is

essentially a comment so you can see

that I've done three quotation marks

here that you put at the top of a

function that describes what the

function does the parameters that it

takes and the return type or what that

return value actually is now this is

super important because the MCP server

will be able to read this and see what

this tool actually does and if it should

be using it so sure you can give it a

descriptive name like add notes but if

you want to be more specific you put

that in the dock string and this will

really dictate how well your tools work

and how often they get called so I

actually have a dock string that I'm

just going to copy in here it doesn't

follow this exact format uh but that's

fine and you can see that it says append

a new note to a sticky note file

arguments message string this note uh

the note content to be added and it says

returns a string confirmation message

indicating the note was saved okay so

now we've documented this tool so that

the AI actually knows when to use it so

let's try to test this out now before we

move on to the next step so we're going

to open up Claude and I just want to go

back here to new chat i want to look

here and see what we have and it still

has ad right it's still running that old

MCP so what we need to do again is we

need to shut this down so we're going to

go to task manager we're going to search

for claude okay we're going to end the

task and then we're just going to wait a

second reboot it and it should now run

our new MCP server and that's because

it's kind of running in the background

so here now if we look at this you can

see that we have add note so for add

note I'm going to say can you add a

note saying Tim is the best okay and

let's see what it says

and it says I'll add that note for you

and then notice it's asking us to use

this tool so I'm going to allow that for

the chat this is the message okay I

saved the note and then we can see kind

of the result here it said note saved

and then if we come here to PyCharm we

actually don't see the notes.txt file

and the reason for that is that it's

saving relative to the location where

the UV command is running or at least

where uh the MCP or sorry Claude is

running our MCP server so that's

actually something good we need to

hardcode the path where we want to save

notes.txt because right now it's kind of

saving in like a random location that we

don't have access to which I just

realized when we were running this so

what I'm going to do is quickly change

this so it's going to be relative to

where this current file is so it saves

it in this directory so we'll be able to

access it later okay so I just adjusted

this here this should now make it so

that it's always going to save it in the

same directory uh where this current

main.py file is so we did os.path.join

we got the directory name of this file

so underscore

file and then we have

notes.txt now I'm not sure if that's

going to work right now we could close

this and rerun it but let's move on to

the next function then we can test it

out after that all right so I'm going to

do this one a little bit faster i'm

going to say mcp.tool and I want this

one to be one that can read a file so

I'm going to say define read notes okay

this is going to return a string i'm

just going to copy in the dock string

i'll put all this code in the

description i just want to save us a

little bit of time here then I'm going

to say with and I'm just going to go

with my autocomplete because now it's so

damn good with notes file we're going to

open this in R mode which stands for

reading so it's not going to modify the

file we're going to say content is equal

to F read and then dot strip this is

just going to remove any new line

characters or white spaces at the end

then we're going to say return content

or we're going to say no content or no

notes yet okay so that if we don't have

any content then we'll just return no

notes yet instead okay so now we have an

add note and a read note and I want to

move on and add a resource now to add

the resource we're going to say at MCP

and this time we're going to say

resource now the resource is different

it's not a tool it's more like just

reading information so in this case we

could do something like getting the most

recent note so to do that we're going to

call this notes colon slash and then

latest okay now there's ways to embed

dynamic variables inside of your

resource for example if I go back here

let me just bring this up uh and we look

at the resource let me find where the

resource is we should be able to see

here that you can do something like this

so you can say like users user

ID/profile and then you can see that you

can put a user ID as a parameter we

don't need to do that for our notes but

that is something you can do with the

resource wanted to mention that but here

we're just saying okay you can get the

notes latest resource that's how we're

referring to it then we're going to say

get latest note this is going to return

a string and for the latest note again

we're going to ensure the file we can

actually just copy this cuz it's going

to be the same thing and this time we're

going to get the read

lines okay we're going to call this

lines and then what we're going to do is

return lines

one strip if lines else we're going to

say no notes yet okay so what this is

saying is all right we're going to get

the most recent line or the last line

we're going to strip off any of the new

line or whitespace characters then we're

only going to do that if lines so if

this list actually has at least one

value so we don't get an index error

otherwise we're just going to say no

notes yet okay so that's a resource and

then lastly I'm going to bring in a

prompt so I'm going to say atmc.prompt

prompt for the prompt we're going to say

define and then this is going to be note

summary_prompt okay if we can spell this

correctly and then this is going to be

of type string and then inside of here

what we're going to do is we're actually

just going to give a prompt that will

summarize all of the notes that

currently exist because that's something

that we might want to do so I'm going to

say with open uh notes file r uh as f

I'm going to say content equals and

again f read.strip we should really put

that into a function because it's very

repetitive but for now that's fine we're

going to say if not content then we're

going to say return there are no notes

yet okay otherwise we can return an

fstring and this is going to say

summarize the current notes and then

inside of here we are going to put the

content okay so this is just a reusable

prompt uh that again we can pull in from

the MCP server now for both of these

again I'm just going to copy in from my

other monitor here a few of the doc

strings to make them a bit clear so

generate a prompt asking the AI to

summarize all the current notes okay and

then for the latest note same thing now

I know this example is quite simple but

you can imagine that if you had an

advanced prompt with multiple values and

variables and things that you could just

put that in this function and then you

can just keep reusing that prompt over

and over and over again and it can grab

external data if it needs to same thing

for the resource again quite simple but

if you had a resource like a large

database you want to run a SQL query all

the time or something you could put that

into a resource and then your AI agent

can continue to use that similarly to a

tool okay so that is our code for our

MCP server same thing again we need to

close down claude so let's close this

down i need to get this thing here and

press end task and then let's rerun it

and test this out and make sure that

it's all working okay so we can see now

we have two tools available add note and

read notes and we have this connection

and you can see that we can get the note

summary prompt or we can get notes

latest for example and we can bring that

in as kind of extra context to our

prompt so I can say you know what are

the notes or something and let's see

what it says says based on the

information there are no notes yet okay

totally fine and you can see here now in

PyCharm this notes file got created so

let's make a few notes so let's go make

10 notes on monkeys okay and let's see

if it uses our MCP server to do that so

let's go allow for this chat and it has

a message it's using the add note

function and it's just going to keep

doing this and you can see behind me

notes are getting populated in this

notes.txt file so let's wait for that to

finish and then we can use the other

tools all right so that is done now

let's try to use maybe our prompt so

let's go to uh here and let's go the

note summary prompt and let's just go

enter here and let's just use this

prompt and see I've shared document

called note summary prompt contain 10

monkey notes I just created for you

appears to asking for a summary of these

notes would you like me to create a

concise summary and I'm going to say yes

okay so run this prompt i'll summarize

the notes about the monkeys for you and

then you can see that it's running add

note okay that's interesting that's not

what I wanted it to do but what it did

is it actually added a note to my notes

file that contained the summary so

monkey summary uh interesting kind of

proves that I guess you know you need to

be a little bit more specific here but

let's say can you get the latest note uh

and let's see if it will do that for us

okay I'll retrieve the latest note it's

getting read note okay let's do this

and let's see okay it gets the notes and

it says monkey summary this is the

latest note blah blah blah okay you guys

get the idea you can mess around with

this obviously you don't need me just to

play with this you know stupid example

um in this video but the point of this

was to show you how to make a custom MCP

server in Python and hopefully not over

complicate the process in my opinion

this is so damn cool because the types

of things you can do with this are

really just endless like even right now

when I'm running this I'm imagining all

of the times in the past where I've

needed to like manually create fake data

and add that to my database now I could

have an MCP server i could connect that

to Claude i could say "Claude make 100

fake users for me." And it can just do

that in my database i don't need to like

manually copy and paste them or run some

custom script i just connect it to a

tool that goes and does whatever I need

now that's obviously a simple example

you can get crazy with this but think

about how cool these MCP servers

actually are and really what you can do

if you have a little bit of imagination

so I hope you guys enjoyed the video if

you did make sure to leave a like

subscribe to the channel and I will see

you in the next one

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