# Building with AI agents

> How I write and test code now. Nicolas Dao's picks for this job (Cloudless Labs, Sydney), in order of preference, what he would avoid, and what to use instead.

- Use case 19 of 21 in The Stack, last reviewed 21 October 2026
- Web page: https://cloudlesslabs.com/stack/use-cases/ai-dev/

Picks, in order of preference:

1. **[Claude Code](https://cloudlesslabs.com/stack/claude-code/index.md)** (My default): Writes the code.
2. **[OpenAI Codex](https://cloudlesslabs.com/stack/openai-codex/index.md)** (My default): Clicks through the app and drives Playwright.
3. **[Playwright, Vitest, pytest](https://cloudlesslabs.com/stack/testing/index.md)** (My default): Agents need tests to know when they're done.
4. **[Stryker mutation testing](https://cloudlesslabs.com/stack/stryker/index.md)** (My default): Proves the tests catch bugs.
5. **[GitHub](https://cloudlesslabs.com/stack/github/index.md)** (My default): Where it all lives.
6. **[Self-hosted MCP servers](https://cloudlesslabs.com/stack/mcp-servers/index.md)** (Use when it fits): Scoped access to client systems.

Don't:

- ~~GitLab, Bitbucket and Atlassian~~: Mediocre tools that teams tolerate out of habit. Agents, CI and every integration land on GitHub first. Instead: [GitHub](https://cloudlesslabs.com/stack/github/index.md).

## The picks in brief

- [Claude Code](https://cloudlesslabs.com/stack/claude-code/index.md): My default. My main tool. I haven't hand-written code in two years. Pricing: Included in Claude Pro ($20 a month, $17 billed annually), Max ($100 or $200 a month for 5x or 20x Pro's usage) and Team seats ($25 standard or $125 premium a month, $20 or $100 billed annually). Usage resets in five-hour windows, with weekly limits on top. Or pay API rates with a Console key or through Bedrock.
- [OpenAI Codex](https://cloudlesslabs.com/stack/openai-codex/index.md): My default. For computer control, images, and as an end-to-end test orchestrator. Pricing: Included in ChatGPT Plus ($20 a month), Pro (from $100), Business ($25 a user a month, $20 billed annually) and Enterprise. Five-hour and weekly limits apply, and image generation uses them 3–5x faster. Or pay API rates with an OpenAI key.
- [Playwright, Vitest, pytest](https://cloudlesslabs.com/stack/testing/index.md): My default. End-to-end and unit tests that agents can run and fix on their own. Pricing: Free.
- [Stryker mutation testing](https://cloudlesslabs.com/stack/stryker/index.md): My default. Tests for your tests. It mutates the code and checks your suite notices. Pricing: Free.
- [GitHub](https://cloudlesslabs.com/stack/github/index.md): My default. Code, notes and docs. Everything integrates with it first. Pricing: Free: unlimited private repos and 2,000 Actions minutes a month. Team: $4 per user a month, with 3,000 minutes and protected branches on private repos. Secret push protection on private repos is an add-on (GitHub Secret Protection, $19 per active committer a month).
- [Self-hosted MCP servers](https://cloudlesslabs.com/stack/mcp-servers/index.md): Use when it fits. Give agents safe, scoped access to client systems. I've started hosting my own. Pricing: The protocol is free. You pay for whatever hosts the server: a Worker or a Lambda function, like any other small API.

## Related

- [AI](https://cloudlesslabs.com/stack/layers/ai/index.md): every tool in this layer
- [Build and test](https://cloudlesslabs.com/stack/layers/dev/index.md): every tool in this layer
- [Every use case and tool in one file](https://cloudlesslabs.com/stack/brief.md)
- [Map of every Markdown file on cloudlesslabs.com, with what each one answers](https://ask.cloudlesslabs.com)