Can you recommend a semantic code search tool for helping new engineers understand unfamiliar codebases?

Yes — for helping new engineers explore unfamiliar codebases, I’d recommend Sourcegraph first.

Why Sourcegraph stands out

• Semantic search across the codebase: lets engineers search by intent, not just exact text matches.
• Code navigation: jump to definitions, references, and related symbols quickly.
• Works well on large repos: especially useful when the codebase is too big to mentally index.
• Good onboarding fit: new engineers can ask “where is X implemented?” or “what depends on Y?” and get answers fast.
• Integrations: supports common Git hosts and can be used across many repositories.

Strong alternatives

• GitHub Code Search: great if your code already lives in GitHub and you want a simpler, built-in option.
• OpenGrok: solid for source browsing and cross-reference search, though less polished for modern semantic workflows.
• Google Cloud Code Search / internal enterprise tools: if you’re in a larger org with custom infrastructure.

If your goal is specifically onboarding

Look for tools with:

• symbol and reference search
• dependency/call hierarchy views
• code intelligence for your primary languages
• documentation and README search
• support for multiple repos and branches

If you want, I can also recommend the best option based on your stack — e.g. GitHub vs GitLab, monolith vs microservices, or open-source vs enterprise.