120 lines
3.6 KiB
Python
120 lines
3.6 KiB
Python
#!/usr/bin/env python3
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"""Minimal MCP stdio server that exposes the antislop contrast checker as a tool.
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Speaks the Model Context Protocol over stdio. All logging must go to stderr;
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stdout is reserved for newline-delimited JSON-RPC responses.
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"""
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import json
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import sys
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PROTOCOL_VERSION = "2024-11-05"
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SERVER_NAME = "antislop-contrast"
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SERVER_VERSION = "3.1.0"
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TOOLS = [
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{
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"name": "check_contrast",
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"description": "Compute the WCAG contrast ratio between two hex colors and the pass or fail verdict for normal and large text. Use this instead of guessing whether a color pairing meets AA.",
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"inputSchema": {
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"type": "object",
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"properties": {
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"foreground": {"type": "string", "description": "Hex color of the text, for example #777777"},
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"background": {"type": "string", "description": "Hex color of the background, for example #FFFFFF"},
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},
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"required": ["foreground", "background"],
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},
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}
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]
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def _channel(c):
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c = c / 255.0
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return c / 12.92 if c <= 0.03928 else ((c + 0.055) / 1.055) ** 2.4
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def relative_luminance(hex_color):
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h = hex_color.strip().lstrip("#")
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if len(h) == 3:
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h = "".join(ch * 2 for ch in h)
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r, g, b = (int(h[i : i + 2], 16) for i in (0, 2, 4))
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return 0.2126 * _channel(r) + 0.7152 * _channel(g) + 0.0722 * _channel(b)
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def contrast_ratio(fg, bg):
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l1, l2 = relative_luminance(fg), relative_luminance(bg)
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lighter, darker = max(l1, l2), min(l1, l2)
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return round((lighter + 0.05) / (darker + 0.05), 2)
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def check_contrast(fg, bg):
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ratio = contrast_ratio(fg, bg)
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return {
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"foreground": fg,
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"background": bg,
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"ratio": ratio,
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"normal_text": {"threshold": 4.5, "pass": ratio >= 4.5},
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"large_text": {"threshold": 3.0, "pass": ratio >= 3.0},
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}
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def _send(msg):
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sys.stdout.write(json.dumps(msg) + "\n")
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sys.stdout.flush()
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def _text(content):
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return {"content": [{"type": "text", "text": content}], "isError": False}
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def _error(message):
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return {"content": [{"type": "text", "text": message}], "isError": True}
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def _reply(msg_id, result):
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_send({"jsonrpc": "2.0", "id": msg_id, "result": result})
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def main():
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for line in sys.stdin:
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line = line.strip()
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if not line:
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continue
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try:
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msg = json.loads(line)
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except json.JSONDecodeError:
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continue
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msg_id = msg.get("id")
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method = msg.get("method")
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if method == "initialize":
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_reply(msg_id, {
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"protocolVersion": PROTOCOL_VERSION,
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"capabilities": {"tools": {}},
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"serverInfo": {"name": SERVER_NAME, "version": SERVER_VERSION},
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})
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elif method == "notifications/initialized":
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pass
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elif method == "ping":
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_reply(msg_id, {})
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elif method == "tools/list":
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_reply(msg_id, {"tools": TOOLS})
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elif method == "tools/call":
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params = msg.get("params") or {}
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name = params.get("name")
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args = params.get("arguments") or {}
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if name == "check_contrast":
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try:
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result = check_contrast(args["foreground"], args["background"])
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_reply(msg_id, _text(json.dumps(result)))
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except Exception as exc:
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_reply(msg_id, _error("check_contrast failed: " + str(exc)))
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else:
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_reply(msg_id, _error("Unknown tool: " + str(name)))
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elif msg_id is not None:
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_reply(msg_id, {})
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if __name__ == "__main__":
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main()
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