docs: add guide on building custom extensions (#806)

examples/mcp-wiki/src/mcp_wiki/__init__.py

@@ -0,0 +1,15 @@
+import argparse
+from .server import mcp
+
+def main():
+    """MCP Wiki: read Wikipedia articles and convert them to Markdown."""
+    parser = argparse.ArgumentParser(
+        description="Gives you the ability to read Wikipedia articles and convert them to Markdown."
+    )
+
+    _ = parser.parse_args()
+    mcp.run()
+
+
+if __name__ == "__main__":
+    main()

examples/mcp-wiki/src/mcp_wiki/__main__.py

@@ -0,0 +1,3 @@
+from mcp_wiki import main
+
+main()

examples/mcp-wiki/src/mcp_wiki/server.py

@@ -0,0 +1,63 @@
+# server.py
+
+import requests
+from requests.exceptions import RequestException
+from bs4 import BeautifulSoup
+from html2text import html2text
+
+from mcp.server.fastmcp import FastMCP
+from mcp.shared.exceptions import McpError
+from mcp.types import ErrorData, INTERNAL_ERROR, INVALID_PARAMS
+
+mcp = FastMCP("wiki")
+
+@mcp.tool()
+def read_wikipedia_article(url: str) -> str:
+    """
+    Fetch a Wikipedia article at the provided URL, parse its main content,
+    convert it to Markdown, and return the resulting text.
+
+    Usage:
+        read_wikipedia_article("https://en.wikipedia.org/wiki/Python_(programming_language)")
+    """
+
+    try:
+        # Validate input
+        if not url.startswith("http"):
+            raise ValueError("URL must start with http or https.")
+
+        response = requests.get(url, timeout=10)
+        if response.status_code != 200:
+            raise McpError(
+                ErrorData(
+                    INTERNAL_ERROR,
+                    f"Failed to retrieve the article. HTTP status code: {response.status_code}"
+                )
+            )
+
+        soup = BeautifulSoup(response.text, "html.parser")
+
+        content_div = soup.find("div", {"id": "mw-content-text"})
+        if not content_div:
+            raise McpError(
+                ErrorData(
+                    INVALID_PARAMS,
+                    "Could not find the main content on the provided Wikipedia URL."
+                )
+            )
+
+        # Convert to Markdown
+        markdown_text = html2text(str(content_div))
+        return markdown_text
+
+    except ValueError as e:
+        # Raised when input parameters are invalid
+        raise McpError(ErrorData(INVALID_PARAMS, str(e))) from e
+    except RequestException as e:
+        # Network or connection errors
+        raise McpError(ErrorData(INTERNAL_ERROR, f"Request error: {str(e)}")) from e
+    except Exception as e:
+        # Catch-all for any other unexpected errors
+        raise McpError(ErrorData(INTERNAL_ERROR, f"Unexpected error: {str(e)}")) from e
+
+