Kiro did it: Building a Credit Card Account Status Check Lambda Using the Kiro IDE!

Hi! I’m Girish, an AWS Community Builder and Cloud Tech Enthusiast, with expertise in delivering customer-focused and business-impacting cloud transformation programs of high complexity.

In my previous articles, I shared various Kiro features like vibe coding, specs driven development, steering docs and hooks.

I also demonstrated various examples of Kiro use cases like creating a CRUD API, using Kiro to modernize my portfolio web site and using Kiro Powers to create postman collection.

In this article, I’ll demonstrate how I used the Kiro IDE to build a real-world banking Lambda function - a Credit Card Account Status Check Lambda - and how Kiro’s context-aware, agentic approach helped me go from idea to a clean, test ready implementation for enterprise workflow.

What Did I Build and Why?

In my prior posts, I demonstrated various other uses cases of Kiro like creating APIs, UI, Modernize my portfolio website and using Kiro Powers. This time I wanted to build a serverless function that contains business logic and does not integrate with any database. The intent of this function is to have a business function that can be triggered by other events and services as needed by the workflow.

With this use case in consideration, I build a credit card account status check Lambda function as account status check is a common patter in banking and credit card platforms.

This Lambda is responsible for determining whether a card account is eligible to process transactions based on signals such as:

• Account status (active vs closed)
• Temporary freezes
• Fraud blocks
• Delinquency thresholds
• Card expiration

This type of logic is typically part of authorization or decisioning workflows, and it’s a great example of pure business logic that:

• Does not require DynamoDB
• Does not require API Gateway
• Can be triggered via events or scheduled checks

I chose this use case intentionally because it allows us to focus on decision logic and architecture, not infrastructure plumbing.

Why Use Kiro for This?

What makes this exercise interesting is not just what we’re building, but how we’re building it.

Instead of starting with:

• Boilerplate SAM templates
• Manual handler code writing
• Trial-and-error refactoring

I let Kiro act as my peer engineer, guiding the implementation through prompts, reasoning about the workspace, and generating code that aligned with real-world banking patterns. Kiro not only generated a fully functional code but also create an Infra as Code template to build and deploy the Lambda function using AWS SAM. In addition, it created specs and design for the function as well.

Architecture

At a high level, the architecture is intentionally simple:

• AWS Lambda (Python) for business logic
• AWS SAM for infrastructure as code
• Event-driven invocation (local testing or scheduled execution)

Reference Architecture Diagram

How Kiro and I Built the Lambda

I started by providing Kiro a prompt.

I explained in detail to Kira the intent of what the Lambda should do and why!

Here is the exact prompt I used:

Kiro responded by:

• Evaluating the existing workspace
• Suggesting a clean project structure
• Generating a Python-based Lambda handler
• Creating a SAM template aligned with best practices

What stood out immediately was that Kiro did not blindly generate code.

It reasoned about:

• Business rules
• Decision paths
• Environment-based configuration
• Security and clarity

The entire experience felt like pair programming with a senior engineer.

Business Logic in Action

The Card Account Status Check Lambda evaluates multiple conditions and produces a clear decision outcome:

• Approved
• Declined
• Review

Kiro created a detailed specs in the form of requirements file. An example shown below:

These specs clearly outline the requirements used by Kiro to build the business function.

Here is an example of AWS SAM template generated by Kiro:

Here is the sample function code generated by Kiro:

Testing the Lambda Locally

Thanks to Kiro as it generated a SAM template. Using SAM, I can test this Lambda function locally by passing multiple test events and Yes, those test JSON was also created by Kiro!

Multiple JSON test files created by Kiro allowed me to test below scenarios:

• Active account
• Frozen account
• Fraud-blocked account
• Delinquent account
• Expired card

Example of test case run locally using AWS SAM.

Once fully built, Kiro provided me final status message of the build process confirming and summarizing what all have been built.

The full function build, including test file generation, was completed in about 60 minutes through peer-style prompt refinement with Kiro.

Conclusion

In this article, I demonstrated how the Kiro IDE can be used to build a real-world Credit Card Account Status Check Lambda—not as a proof of concept, but as a practical, enterprise-aligned implementation.

What stood out most was the quality of collaboration:

• Kiro reasoned about business intent
• Generated clean, explainable code
• Adapted as requirements evolved
• Responded like a true peer programmer

Generative AI isn’t replacing good coding, design or testing practices; it’s enhancing them. And with tools like Kiro, building business functions can feel like working alongside an experienced software engineer who understands your workspace.

As agentic AI tools continue to mature, capabilities like specs driven development, context-aware reasoning, and explainable outputs will become essential especially in regulated domains like banking.

I believe this is just the beginning, and tools like Kiro will continue to redefine how we design & build cloud-native systems.

Thanks for reading, and stay tuned for more hands-on AWS and Kiro content!

Watch the video here:

Thanks,

𝒢𝒾𝓇𝒾𝓈𝒽 ℬ𝒽𝒶𝓉𝒾𝒶
𝘈𝘞𝘚 𝘊𝘦𝘳𝘵𝘪𝘧𝘪𝘦𝘥 𝘚𝘰𝘭𝘶𝘵𝘪𝘰𝘯 𝘈𝘳𝘤𝘩𝘪𝘵𝘦𝘤𝘵
𝘈𝘞𝘚 𝘊𝘦𝘳𝘵𝘪𝘧𝘪𝘦𝘥 𝘋𝘦𝘷𝘦𝘭𝘰𝘱𝘦𝘳 𝘈𝘴𝘴𝘰𝘤𝘪𝘢𝘵𝘦
𝘈𝘞𝘚 𝘊𝘦𝘳𝘵𝘪𝘧𝘪𝘦𝘥 𝘎𝘦𝘯𝘈𝘐 𝘗𝘳𝘢𝘤𝘵𝘪𝘵𝘪𝘰𝘯𝘦𝘳
𝘈𝘞𝘚 𝘊𝘭𝘰𝘶𝘥 𝘛𝘦𝘤𝘩𝘯𝘰𝘭𝘰𝘨𝘺 𝘌𝘯𝘵𝘩𝘶𝘴𝘪𝘢𝘴𝘵