Building custom AI agents is easier than ever. OpenAI's API, Claude's tool use, LangChain, CrewAI — the building blocks are available. So every engineering team asks: should we build our own code intelligence agent?
The answer depends on what you actually need.
When to Build
Build your own when:
- You need domain-specific reasoning that no commercial tool covers (medical device firmware, classified systems)
- Your security requirements prohibit any commercial tool (air-gapped environments)
- The scope is narrow (one specific workflow, not general intelligence)
- You have ML/AI engineering expertise on the team
When to Buy
Buy when:
- You need codebase-level intelligence (feature discovery, dependency graphs, knowledge extraction). Building this takes 6-12 months of dedicated engineering.
- You need cross-language support (parsing TypeScript, Python, Java, Go). Each language parser is months of work.
- You need it now (the Understanding Tax costs real money every sprint you don't address it)
- Your AI engineers should be building product, not internal tools
The Build Trap
The typical "build" trajectory:
- Month 1: Excited team builds a RAG pipeline over the codebase. Demo looks great.
- Month 3: Edge cases emerge. The pipeline hallucinates on large files. Parsing breaks on TypeScript decorators.
- Month 6: One engineer is maintaining the agent full-time. It handles 40% of use cases well, 60% poorly.
- Month 12: The team realizes they've built a code search tool with a chat interface — not code intelligence.
The gap between "RAG over codebase" and "actual code intelligence" is enormous. RAG gives you semantic search. Intelligence requires dependency graphs, feature clustering, call path tracing, git history analysis, and knowledge extraction.
The Middle Ground
Use commercial tools for codebase intelligence (the hard, non-differentiating infrastructure). Build custom agents on top for your specific workflows. This gives you the best of both: deep codebase understanding from a tool that's spent years building it, plus custom automation for your unique needs.
Originally published on glue.tools. Glue is the pre-code intelligence platform — paste a ticket, get a battle plan.
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