Alistair Gray published part two of Stripe’s “Minions” series, going deeper on how they built their internal coding agents. It’s a great read throughout, but three ideas really stood out to me.

First, blueprints. These are workflows that mix deterministic steps with agentic ones:

Blueprints are workflows defined in code that direct a minion run. Blueprints combine the determinism of workflows with agents’ flexibility in dealing with the unknown: a given node can run either deterministic code or an agent loop focused on a task. In essence, a blueprint is like a collection of agent skills interwoven with deterministic code so that particular subtasks can be handled most appropriately.

If you know a step should always happen the same way, don’t let an LLM decide how to do it. Let the agent handle the ambiguous parts, and hardcode the rest (this can also dramatically reduce token cost).

Second, their centralized MCP server:

We built a centralized internal MCP server called Toolshed, which makes it easy for Stripe engineers to author new tools and make them automatically discoverable to our agentic systems. All our agentic systems are able to use Toolshed as a shared capability layer; adding a tool to Toolshed immediately grants capabilities to our whole fleet of hundreds of different agents.

A shared tool layer that all agents can use… 500 tools, one server, hundreds of agents. Very cool idea.

And third, what they call “shifting feedback left”:

We have pre-push hooks to fix the most common lint issues. A background daemon precomputes lint rule heuristics that apply to a change and caches the results of running those lints, so developers can usually get lint fixes in well under a second on a push.

If you can catch a problem before it hits CI, do it there. A sub-second lint fix on push is better than a 10-minute CI failure, whether you’re a person or an LLM burning tokens.

So much of Stripe’s agent success is built on top of investments they made for human developer productivity. Good dev environments, fast feedback loops, shared tooling. The agents benefit from all of it, and developers remain in control.