How do high-level and low-level solution designs differ?

Question

IT Interview Practice · Accepted Answer

**High-level design (HLD)** explains the solution’s major parts and how they work together. **Low-level design (LLD)** specifies enough detail to implement those parts consistently. These are useful working terms; organizations do not share one mandatory document template.

## Follow one decision through both levels

For a returns portal, HLD identifies the portal, returns service, order system and warehouse integration. It states which system owns each record and which interactions are asynchronous.

LLD describes a particular interaction: request fields, validation, state transitions, duplicate handling, database constraints and error responses. An engineer should be able to implement it, and a tester should know the expected behavior.

## Keep them connected

- HLD serves cross-team alignment and architectural review.
- LLD supports implementation and detailed testing.
- Both reference the same requirements, terminology and important decisions.

If HLD promises safe retries but LLD has no duplicate-detection rule, the documents disagree. Trace a concrete failure case across both to discover that gap.

## Interview pitfall

Do not distinguish them only by page count or diagram size. Explain the audience and decisions each view enables. Avoid freezing every implementation detail too early; develop risky details first and update the broader design when implementation evidence changes an assumption.

Follow one decision through both levels

Keep them connected

Interview pitfall

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