Validate a chat message

Background

Before sending messages to an LLM, it's worth checking each one is well-formed: a dict with a known role and a string content. A malformed message (missing content, an unknown role) is a common, silent bug.

Valid roles in this course: "system", "user", "assistant".

Problem statement

Implement is_valid_message(msg) returning whether msg is a well-formed chat message.

Input

• msg — any value (expected to be a message dict).

Output

Returns a bool: True iff msg is a dict with msg["role"] in {"system", "user", "assistant"} and msg["content"] a str.

Examples

Example 1 — valid

Input:  {"role": "user", "content": "hi"}
Output: True

Example 2 — bad role

Input:  {"role": "bot", "content": "hi"}
Output: False

Example 3 — non-string content

Input:  {"role": "system", "content": 123}
Output: False

Constraints

• Must be a dict.
• role ∈ {"system", "user", "assistant"}.
• content is a str.

Notes

• Catch malformed messages early — a missing content key turns into a confusing provider-side error otherwise.