# Brex Engineering Blog

Learn about Brex's engineering efforts, product developments, lessons learned, and more.


**URL Source:** https://www.brex.com/journal/engineering-blog

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Brex Engineering Blog

Tech, architecture, innovation

## Related Articles

### [Not all MCPs are created equal](https://www.brex.com/journal/not-all-mcps-are-created-equal)
**Description:** Two MCP servers can look identical on paper and behave nothing alike. Here are the three questions that tell them apart.
**Excerpt:** Two MCP servers can look identical on paper and behave nothing alike. Here are the three questions that tell them apart.

### [Agent automations for big migrations: How we accelerated framework upgrades by 32x with Cursor](https://www.brex.com/journal/agent-automations-for-big-migrations)
**Description:** How we arrived at this highly efficient system, along with the missteps we made along the way that are worth understanding.
**Excerpt:** How we arrived at this highly efficient system, along with the missteps we made along the way that are worth understanding.

### [Long-running agents don't need tools or hosted sandboxes; all they need is bash.](https://www.brex.com/journal/long-running-agents-need-bash)
**Description:** Brex rebuilt its expense audit agent on a bash workbench instead of native tools. Token usage dropped ~80%, and recall climbed at scale. Learn more.
**Excerpt:** Brex rebuilt its expense audit agent on a bash workbench instead of native tools. Token usage dropped ~80%, and recall climbed at scale. Learn more.

### [How we built an agent that turns customer feedback into shipped fixes](https://www.brex.com/journal/agent-that-turns-customer-feedback-into-shipped-fixes)
**Description:** Brex built an agent workflow that reads customer feedback across tools, finds quality of life improvement opportunities, and fixes them. Here's how it works.
**Excerpt:** Brex built an agent workflow that reads customer feedback across tools, finds quality of life improvement opportunities, and fixes them. Here's how it works.

### [AI cost visibility is a problem for every company. Here's how we're solving it.](https://www.brex.com/journal/magpie-ai-cost-visibility-dashboard)
**Description:** Traditional spend management can't handle the complexity of AI costs, so we built Magpie, an internal tool that provides real-time visibility of AI spending.
**Excerpt:** Traditional spend management can't handle the complexity of AI costs, so we built Magpie, an internal tool that provides real-time visibility of AI spending.

### [How we built an AI oncall engineer at Brex](https://www.brex.com/journal/how-we-built-an-ai-oncall-engineer)
**Description:** We encoded our oncall playbook into an agent. Here's what happened.
**Excerpt:** We encoded our oncall playbook into an agent. Here's what happened.
**Tags:** Expense management, AI

### [When your infrastructure tool's best interface is a web page, you have an agent problem](https://www.brex.com/journal/terminal-ui-became-an-agent-interface)
**Description:** We built a terminal UI to replace a browser tab. Then we realized we'd built something agents could use too.
**Excerpt:** We built a terminal UI to replace a browser tab. Then we realized we'd built something agents could use too.
**Tags:** Expense management, AI

### [CrabTrap: an LLM-as-a-judge HTTP proxy to secure agents in production](https://www.brex.com/journal/building-crabtrap-open-source)
**Description:** Here's what we learned in building and open-sourcing CrabTrap, and why we believe it’s a major step forward in the security of agent harnesses.
**Excerpt:** Here's what we learned in building and open-sourcing CrabTrap, and why we believe it’s a major step forward in the security of agent harnesses.

### [Building autonomous agents for technical tasks: 5 lessons learned](https://www.brex.com/journal/building-autonomous-agents-for-technical-tasks)
**Description:** Brex built a general-purpose template for delegating engineering work to agents with confidence. Here's how we did it and what we learned.
**Excerpt:** Brex built a general-purpose template for delegating engineering work to agents with confidence. Here's how we did it and what we learned.
**Tags:** AI

### [What if 90% of your prompt is content you can't control?](https://www.brex.com/journal/articles/what-if-you-cant-control-your-prompt)
**Description:** Discover how Brex's audit agent handles messy, real-world context, and why good AI products give judgment a structure to operate inside, not a script to follow.
**Excerpt:** Discover how Brex's audit agent handles messy, real-world context, and why good AI products give judgment a structure to operate inside, not a script to follow.
**Tags:** Expense management, AI

### [How we test our agents: by committing fraud](https://www.brex.com/journal/articles/simulation-testing-ai-audit-agent)
**Description:** Simulation testing lets you find out how good your agent actually is before the world shows you. Here's what we've learned in teaching agents to catch fraud.
**Excerpt:** Simulation testing lets you find out how good your agent actually is before the world shows you. Here's what we've learned in teaching agents to catch fraud.
**Tags:** Expense management, AI

### [The future of financial reporting is not a chart](https://www.brex.com/journal/articles/the-future-of-financial-reporting-is-not-a-chart)
**Description:** Meet Brex Spaces, an AI-powered workspace for finance teams that goes beyond charts to deliver powerful insights, instantly.
**Excerpt:** Meet Brex Spaces, an AI-powered workspace for finance teams that goes beyond charts to deliver powerful insights, instantly.
**Tags:** Expense management, AI