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Intuit·Software Engineer·Technical Phone Screen·Senior

Senior
Jun 2026

Summary

Intuit software engineer interview that went pretty deep on LLM reliability, specifically around getting APIs to return clean JSON without any extra noise. One question but it had a lot of layers, felt more like a mini system design session than a typical coding screen.

Questions Asked (1)

Q1

You need an LLM API to return strict JSON only. How do you structure the prompt and request so the model reliably produces JSON with no extra text? Walk through message roles, schema or tool-calling constraints, parameter choices, runtime enforcement, and how you'd evaluate and iterate on the solution.

System DesignTechnical Trade-offsAPI & Integrations
Author's notes

This one sprawled in a way I didn't expect.

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AI HintsAI Generated

Suggested Approach

Structure your answer as a layered reliability strategy: start with prompt design (clear instructions, system role, few-shot examples), then enforce constraints via API parameters (response_format, tool calling, temperature=0), add runtime validation and retries, and close with an evaluation loop using metrics like JSON validity rate and schema adherence. Emphasize trade-offs between strictness and flexibility, and how you'd iterate based on real-world failures.

Pro tip: Mention that even with strict JSON mode, you should always validate and handle parse errors gracefully—LLMs can still produce invalid JSON under edge cases, so a fallback or retry with a repair prompt is essential for production reliability.

1. Design the prompt and message roles

Use a system message to define the assistant's role and strict output format, then a user message with the task and any few-shot examples of valid JSON. Explicitly instruct 'Return only JSON, no other text.'

2. Leverage API constraints and parameters

Use response_format={'type': 'json_object'} if available, or tool/function calling with a JSON schema. Set temperature=0 and max_tokens appropriately to reduce variability and truncation.

3. Enforce at runtime

Validate the response against a JSON schema (e.g., using Pydantic or jsonschema). If invalid, retry with a repair prompt or fallback logic. Log failures for analysis.

4. Evaluate and iterate

Measure success metrics like JSON validity rate, schema adherence, and latency. Test with diverse inputs, including edge cases, and iterate on prompt, parameters, or schema based on failures.

Key Points to Mention

  • System message to set strict output format and role
  • Few-shot examples of valid JSON in the prompt
  • API parameters: response_format, temperature=0, max_tokens
  • Tool/function calling with JSON schema for structured output
  • Runtime validation with JSON schema and retry/repair logic
  • Evaluation metrics: validity rate, schema adherence, latency, and error analysis

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.