diff --git a/src/ai_typewriter/ai_client.py b/src/ai_typewriter/ai_client.py
new file mode 100644
index 0000000..2783fd2
--- /dev/null
+++ b/src/ai_typewriter/ai_client.py
@@ -0,0 +1,79 @@
+from __future__ import annotations
+
+import requests
+
+from .config import AppConfig
+
+
+class AIClientError(RuntimeError):
+    """Raised when the configured AI backend cannot return text."""
+
+
+def ask_ai(prompt: str, config: AppConfig) -> str:
+    if not prompt.strip():
+        raise AIClientError("Le texte capturé est vide.")
+
+    if config.provider == "ollama":
+        return _ask_ollama(prompt, config)
+    if config.provider == "gemini":
+        return _ask_gemini(prompt, config)
+    raise AIClientError(f"Provider non supporté: {config.provider}")
+
+
+def _ask_ollama(prompt: str, config: AppConfig) -> str:
+    url = f"{config.server_url}/api/chat"
+    payload = {
+        "model": config.model,
+        "stream": False,
+        "messages": [
+            {"role": "system", "content": config.system_prompt},
+            {"role": "user", "content": prompt},
+        ],
+    }
+    try:
+        response = requests.post(url, json=payload, timeout=config.request_timeout_seconds)
+        response.raise_for_status()
+        data = response.json()
+    except requests.RequestException as exc:
+        raise AIClientError(f"Erreur Ollama: {exc}") from exc
+    except ValueError as exc:
+        raise AIClientError("Réponse Ollama invalide: JSON illisible") from exc
+
+    content = data.get("message", {}).get("content")
+    if not isinstance(content, str) or not content.strip():
+        raise AIClientError("Réponse Ollama vide ou inattendue")
+    return content.strip()
+
+
+def _ask_gemini(prompt: str, config: AppConfig) -> str:
+    if not config.api_key:
+        raise AIClientError("api_key est obligatoire pour provider='gemini'.")
+
+    base = config.server_url or "https://generativelanguage.googleapis.com"
+    url = f"{base}/v1beta/models/{config.model}:generateContent"
+    payload = {
+        "systemInstruction": {"parts": [{"text": config.system_prompt}]},
+        "contents": [{"role": "user", "parts": [{"text": prompt}]}],
+        "generationConfig": {"temperature": 0.2},
+    }
+    try:
+        response = requests.post(
+            url,
+            params={"key": config.api_key},
+            json=payload,
+            timeout=config.request_timeout_seconds,
+        )
+        response.raise_for_status()
+        data = response.json()
+    except requests.RequestException as exc:
+        raise AIClientError(f"Erreur Gemini: {exc}") from exc
+    except ValueError as exc:
+        raise AIClientError("Réponse Gemini invalide: JSON illisible") from exc
+
+    try:
+        text = data["candidates"][0]["content"]["parts"][0]["text"]
+    except (KeyError, IndexError, TypeError) as exc:
+        raise AIClientError("Réponse Gemini vide ou inattendue") from exc
+    if not isinstance(text, str) or not text.strip():
+        raise AIClientError("Réponse Gemini vide")
+    return text.strip()