apidays Munich 2025 - Let’s build, debug and test a magic MCP server in Postman with a few clicks, Johannes Nicolai (Postman)

All rights reserved by Postman Inc
Johannes Nicolai - johannes.nicolai@postman.com
Let’s build, debug and test a magic MCP
server in Postman with a few clicks

Agenda
Function Calling /MCP - Physical Hello World Example
Hands-On: Generate and run your own, magic MCP server with Harry Potter & Octocat API
Hands-On: Connect your MCP Server to Claude or VSCode
Hands-On: Debug, and test your MCP server
Q & A
5
4
3
2
1

Getting to know you better - Show off hands …
Who is using Postman and has an account?
Who is using Claude Desktop, GitHub Copilot or Cursor?
Who has already heard of MCP and LLM Function Calling?
Who has connected to an MCP server?
Generated an MCP server?
Wrote a custom MCP server?
Can run node applications locally or docker locally?
Can you access the slides, clone the repo and install deps?
Search for “Fun APIs only” on https://postman.com/explore
select Octodex-HP-MCP server, check description

Function Calling: Connects APIs M
to LLMs N - M x N combinations

The Integration Challenge:
The MN Problem
● Each AI model needs unique
connections to every service.
● This complex setup slows progress
and costs more to maintain.
● Scaling AI is impossible without a
simpler, unified solution

Solution:
Model Context Protocol MCP
● MCP is a standard protocol for AI to
use tools and data.
● It simplifies integration reducing
complexity to MN.
● Scaling AI is impossible without a
simpler, unified solution

MCP  One common protocol for all models and tools M  N
https://patel-world.medium.com/mcp-the-usb-c-of-ai-applications-a95dc77fcbf8

MCP Momentum
A Growing Ecosystem
● MCP is backed by Anthropic,
Google, Microsoft and OpenAI.
● Many companies are rapidly
adopting MCP.
● A large open-source community
supports MCP's growth

MCP Architecture
How It Works
● MCP Hosts are AI apps where users
interact.
● MCP Clients manage secure
connections to Servers.
● MCP Servers expose capabilities
from existing APIs.

MCPGen for Any Collection in the Postman API Network

Berlin style Techno Song from MCP Architecture Confluence Page
Link to Claude Conversation 🎵🔊

Postman as MCP Tool Example - Improve NYT-API and contribute
changes back (Official Postman MCP Server)

Real world example with Siemens Xcelerator, Backstage, Postman
Identifying IOT business cases & API duplicates

Cursor / Co-Pilot connected to MCP servers

Harry Potter API - https://postman.com/explore - Fun APIs only

Octodex API - https://postman.com/explore - Fun APIs only

MCP directly embedded into Postman (Agent Mode)

MCP Trouble Shooting - https://postman.com/explore - Fun APIs only

Our magic example MCP server 🪄 ✨ - Search Fun APIs only

Magic MCP Server Demo Repository - Search GitHub for MCP Octocat

How to expose the Octocats over an API, generate test
cases and performance test it …
All in one Demo - Watch Video

Adding your own APIs to an existing MCP server (example)

Advanced Claude Agent Demo Repo with AWS Bedrock support

Example of advanced Image Generation API exposed via MCP

MCP Security
Best Practices
● For Developers:
○ Prioritize secure credential handling
(secrets managers, short-lived creds,
RBAC
○ Supply chain security (tool vetting, trusted
scanners)
○ Environment isolation (containers,
network controls)
○ Safe coding practices (input validation)
● For Users:
○ Use encrypted clients
○ Enable comprehensive monitoring
○ Stay vigilant (avoid unknown servers,
watch for unusual activity).

getmcp.dev : Postmanʼs curated MCP registry with built-in updates and test env

Donʼt just keep
up with the
future — build it.

MCP Flow
Typical Communication Flow
● User Interaction: User submits a query to
the Host.
● Host Processing & Connection: Host
identifies required external capabilities and
connect to Server(s).
● Capability Discovery & Invocation: Client
queries Server for available tools and
fetches capabilities to use.
● Server Execution and Result: Server
performs an action and returns results to
Client. Client send results to Host.

MCP Transport Protocol Overview
https://blog.stackademic.com/model-context-protocol-mcp-in-ai-9858b5ecd9ce

MCP Message Flow Overview
https://www.soa4u.co.uk/2025/03/apis-arent-dead-they-evolve.html

MCP Concrete Message Flow Example
https://blog.stackademic.com/model-context-protocol-mcp-in-ai-9858b5ecd9ce

Postman API Network
Worldʼs Largest Public API Hub
# of Postman Users
40M
# of Public Workspaces
150K
# of Public APIs
450K

Our new Frankfurt data center on AWS ✨ … magically fast
🪄

… also supported by our Backstage integration ✨

AI adds more players to the game: Employees who are no
dev/domain experts/native speakers can finally participate and
developers get a boost, but new challenges arise

One rule that will never change though: Garbage In → Garbage Out
GenAI will just create larger FrankenstAIn solutions
No AI GenAI

Thousands of Postman teams/Git repos/Static files lead to API
consumer confusion and building “FrankenstAInˮ solutions

With a central internal Postman Team and Public API Network
● See all “goodˮ lego bricks APIs/collections) available
● Discover, Find, Adapt, Evaluate, Collaborate and share in real time with all stakeholders
● See what other teams built with the API lego bricks, build & tests API much better
● Avoid reinventing the wheel / one off integrations (consumers are no longer forced to become producers because
they could not find a proper API
● Start to unlock InnerSource benefits and save thousands of hours of confusion and inefficient collaboration

apidays Munich 2025 - Let’s build, debug and test a magic MCP server in Postman with a few clicks, Johannes Nicolai (Postman)

apidays Munich 2025 - Let’s build, debug and test a magic MCP server in Postman with a few clicks, Johannes Nicolai (Postman)

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