Make AI Return Valid JSON Every Time

#ai #llm #api #programming

Tired of parsing broken JSON from AI responses? Here's how to make AI output perfectly structured JSON — guaranteed, every time.

AI generating broken JSON is the #1 frustration I see developers complain about. Missing braces, trailing commas, random explanations mixed in.

Here's how to fix it.

The Problem

# AI response: "Sure! Here's the data: {"name": "Alice", "age": 30}"
# ← Parse error: "Sure! Here's the data:" is not valid JSON

json.loads(response)  # 💥 json.JSONDecodeError

The Fix: System Prompt + Function Calling

response = client.chat.completions.create(
    model="deepseek-v4-pro",
    messages=[
        {"role": "system", "content": "Always respond with valid JSON only. No markdown. No explanations."},
        {"role": "user", "content": "Extract name and age from: Alice is 30 years old"}
    ],
    response_format={"type": "json_object"}  # ← Force JSON output
)

data = json.loads(response.choices[0].message.content)
print(data)  # {"name": "Alice", "age": 30}  ← Always valid

Real Example: Text Extraction

def extract_entities(text):
    response = client.chat.completions.create(
        model="deepseek-v4-pro",
        messages=[
            {"role": "system", "content": "Extract entities as JSON. Format: {people: [], dates: [], companies: []}"},
            {"role": "user", "content": text}
        ],
        response_format={"type": "json_object"}
    )
    return json.loads(response.choices[0].message.content)

# Works every time — no regex, no parsing hacks
entities = extract_entities("Mark met Sarah at Google on July 3rd")
# {"people": ["Mark", "Sarah"], "companies": ["Google"], "dates": ["July 3rd"]}

Why This Matters

Before	After
Parse errors 30% of time	Parse errors 0% of time
Try/except everywhere	One clean call
Regex hacks to fix JSON	Pure structured data
Can't build on top	Reliable API pipeline