CSC510 Lecture 20

MCP
(20261019)

Transcript

1. CSC 5100 Modern Software Engineering Lecture 20. Model Context Protocol Dr. Javier Gonzalez-Sanchez javiergs@calpoly.edu www.javiergs.phd ffi o ce: 14 -227
6. The problem We already have an HTTP API. How can Claude use it? USER EXISTING SERVICE EXPECTED ANSWER “Convert 86°F to Celsius.” GET /5100/temperature { "result": 30.0 } value=86&from=F&to=C
7. The existing REST contract No changes to TemperatureLambda are required. GET https://api.javiergs.phd/5100/temperature?value=86&from=F&to=C HTTP 200 { "value": 86.0, "from": "F", "to": "C", "result": 30.0 }
8. MCP is a restaurant menu The waiter selects a dish; the kitchen prepares it. Customer Waiter Menu User request Claude MCP tool list Order Kitchen Dish MCP tool call Lambda / REST API Tool result
9. A menu needs descriptions A name alone may not explain what a tool does. BAD MENU USEFUL MENU Dish 1 convert_temperature Dish 2 “Convert Fahrenheit and Celsius” Dish 3 Inputs: value, from, to
10. MCP: two operations Discovery first. Invocation second. 1 tools/list 2 tools/call Server advertises tool names, descriptions, and input schemas. Claude chooses a tool and supplies validated arguments. Claude chooses the tool. The server executes it.
11. MCP From Scratch Our very own MCP server
12. Case A — Build We implement the MCP translation layer in Java. CLAUDE DESKTOP CloudMcpServer.java REST → LAMBDA MCP over stdio Java MCP SDK API Gateway HttpClient TemperatureLambda Claude → Java JAR → HTTP GET → Lambda
17. Build: launch the JAR from Claude Claude Desktop starts the Java process and talks over stdio. "mcpServers": { "csc5100": { "command": "/usr/bin/java", "args": ["-jar", ".../mcp/target/mcp-1.0.jar"] } } f a a a a ~/Libr ry/Applic tion Support/Cl ude/cl ude_desktop_con ig.json
18. Build: follow one request Same menu → order → kitchen → dish. 1 Claude discovers convert_temperature 2 Claude calls with 86, F, C 3 Java callback sends HTTP GET 4 Lambda returns result: 30.0 5 Claude answers “30°C”
19. Build: the observed edge case Claude first tried long unit names, then retried. FIRST CALL RETRY from = "fahrenheit" from = "F" to = "celsius" to = "C" REST API → HTTP 400 REST API → 30.0 Better schemas: enum [F, C] avoids guessing.
20. To be continued...
21. Questions 21
22. CSC 5100 Modern Software Engineering Javier Gonzalez-Sanchez, Ph.D. javiergs@calpoly.edu Fall 2026 Copyright. These slides may be used only as study material for CSC 5100 within the California State University system. They may not be distributed or used for any other purpose.