The 90/10 Rule for AI Agents, A Deep Dive: When To Replace Paid SaaS Tools With a Vibe-Coded Apps. And When Not To.
Summary
The article discusses the 90/10 rule for AI agents, emphasizing when to replace paid SaaS tools with custom-built applications. It highlights lessons learned from building two new apps and the evolving landscape of AI functionality in software.
Why It Matters
As organizations increasingly rely on AI, understanding when to build custom solutions versus using existing tools is crucial. This article provides practical insights for decision-makers on optimizing resources and leveraging AI capabilities effectively.
Key Takeaways
- The 90/10 rule suggests buying 90% of tools off the shelf and building 10% when necessary.
- Organizations should consider replacing tools lacking AI functionality as AI becomes essential.
- Building custom tools can be justified when existing solutions fail to meet specific data needs.
- Utilizing AI tools like Claude Co-work can streamline the development process.
- Defining clear specifications is critical before embarking on building new applications.
The 90/10 Rule for AI Agents, A Deep Dive: When To Replace Paid SaaS Tools With a Vibe-Coded Apps. And When Not To. by Jason Lemkin | Artificial Intelligence (AI), Blog Posts, SaaStr.Ai We’re now nine months into running SaaStr AI as three humans, one dog, and 20+ AI agents. We’ve vibe-coded 8+ apps into production. We’ve bought dozens of third-party AI tools. And in the last two weeks alone, we built two new apps — one internal, one external-facing — that taught us some hard lessons about when to build, when to buy, and why the old rules are changing fast. Here’s the updated playbook. The 90/10 Rule Still Holds — But With a New Exception Our rule from Day 1 has been simple: buy 90% of what you need off the shelf, and only build the 10% where no solution exists. We’re not trying to vibe-code our own CRM. We’re not rebuilding our marketing automation platform. We’re not recreating our outbound SDR agents. All of those have solid third-party tools that do the job well. And when you’re a team of three humans managing 20+ agents and 8+ apps, you simply don’t have the bandwidth to take on compliance, security, data warehousing, and everything else that comes with building from scratch. But here’s the new wrinkle: we now also build when a tool we’re paying for has zero AI functionality. That’s the line. If it’s February 2026 and your product doesn’t have a single AI feature — not even a lightweight one — that’s when we start looking at replacing you. Not because we want to. Beca...
