The server has a single well-defined tool 'weather' with explicit schema, descriptions, and parameter types. However, several quality issues prevent a higher score: (1) Tool name 'weather' lacks a clear action verb (should be 'get_weather' or 'fetch_weather'); (2) Parameter descriptions include examples ('Saint Petersburg', 'en', 'es', 'zh_CN') which LLMs tend to reuse literally; (3) No output schema is documented, the tool returns templated text with no structured field definitions; (4) Default values for 'units' and 'lang' are present but not explicitly stated as optional in the schema annotations; (5) Error handling is minimal, no guidance for LLM recovery on API failures (invalid city, API key missing, rate limits); (6) No input validation of the 'units' enum is shown (only 'c', 'f', 'k' are valid, but the code does not validate this before calling the API). The tool definition itself is visible and properly registered in main.go, so it is not inferred.

• Rename tool from 'weather' to 'get_weather' or 'fetch_current_and_forecast_weather' to include the action verb and clarify intent for LLM dispatch.
• Replace examples in parameter descriptions with enum constraints. Change units description from 'Use "c" for Celsius, "f" for Fahrenheit, or "k" for Kelvin' to an enum: {"type": "string", "enum": ["c", "f", "k"]} and update description to 'Temperature unit (c=Celsius, f=Fahrenheit, k=Kelvin)'.
• Replace examples in lang description with a reference to ISO 639-1 codes instead of listing specific codes. Change to 'Two-letter ISO 639-1 language code (e.g. en, es, de, fr, zh). Default: en.'
• Document the output schema explicitly in the tool description. Example: 'Returns structured weather data including: current (temperature, conditions, humidity, wind, pressure, feels-like), high/low temperatures, sunrise/sunset times, and 5-day forecast with date/time, conditions, and temperature ranges.'
• Add input validation in weatherHandler: validate units ∈ {c, f, k} before API call; return actionable error if invalid (e.g. 'Invalid units: got "x". Must be one of: c, f, k').
• Wrap API calls in error handling that returns recovery guidance. Example: if city not found, return 'City "[city]" not found. Try with the English name or a larger city nearby.' If API key missing, return 'OpenWeather API key not configured. Set OWM_API_KEY environment variable.'
• Return structured JSON output instead of templated text. Replace the template-based response with a JSON object: {"current": {"temp": X, "conditions": [...], "humidity": Y, ...}, "forecast": [{"date": "...", "temp": X, ...}]}. This allows LLMs to extract specific fields without parsing prose.