Hooks do wonders here. The payload contains a lot of information about the pending action the agent wants to make. Combine that with the most recent n events from the agent’s session history and you have a rich enough context to pass to another agent to validate the action through the SDK.

This way the validation uses the same subscription you’re logged in to, whether you’re using Claude Code, Codex, or Copilot. The validation agent responds with a json format that you can easily parse and return, allowing you to let the action through or block it with direction and guidance. I’m genuinely impressed by how well this works considering how simple it is.

You can find my approach here: https://github.com/nizos/probity

I created it to address this exact issue. It is a vendor-neutral ESLint-style policy engine and currently supports Claude Code, Codex, and Copilot.

It uses the agents hooks payloads and session history to enforce the policies. Allowing it to be setup to block commits if a file has been modified since the checks were last run, disallow content or commands using string or regex matching, and enforce TDD without the need of any extra reporter setup and it works with any language.

Feedback welcome: https://github.com/nizos/probity

TDD Guard was built when Claude Code was the only one to offer hooks. Plugins didn't exist and the models were weaker, so the validation context and instructions took more work to get right. This is why it ended up requiring test reporters for different languages.

I have started a new project that does the same TDD enforcement, also through hooks, but without reporters. It works with any test runner, and it is vendor-agnostic, it works with Claude Code, Codex, and GitHub Copilot. The validator also sees recent session history which helps it handle cases like refactoring better.

The TDD instructions are still pretty basic compared to TDD Guard's, which have been dogfooded for a year. One thing I noticed while testing across agents is that some follow TDD a lot better than others, Codex struggled the most with the basic instructions.

Feedback welcome:

https://github.com/nizos/conduct

https://github.com/nizos/tdd-guard

When it comes to agentic coding. I created an open source tool that enforces those practices. The agent gets blocked by a hook if it tries to do anything that violates those principles. I think it helps a lot if I may say so myself.

https://github.com/nizos/tdd-guard

Edit: I realize now that I misunderstood your comment. I was quick to respond.

[ { "key": "shift+enter", "command": "workbench.action.terminal.sendSequence", "args": { "text": "\u001b\n" }, "when": "terminalFocus" }, ]

It will allow you to get new lines without any strange output.

I deliberately picked a vendor-agnostic name. Adding support for other clients mainly means extending IClient:

https://github.com/nizos/tdd-guard/blob/main/src%2Fcontracts...

https://github.com/nizos/tdd-guard/tree/main/src%2Fvalidatio...

I'll take a closer look into adding this support. I'd also welcome a contribution if that's something you would be interested in!

The question is, do other agent platforms support hooks or similar functionality?

Go support was recently added, and TDD-Guard also works with these frameworks:

JavaScript/TypeScript: Vitest and Jest Python: Pytest PHP: PHPUnit Go: Native go test

Adding a new language or framework just means creating a reporter that outputs test results in a format that TDD-Guard can consume.

I'm not familiar with Opencode. Is there something particular that interests you in it?

I believe that using guardrails with agentic coding is far more effective than simply using instructions. This plugin demonstrates it using Test-Driven Development.

TDD-Guard can now be used with Go. Other supported languages are: JS/TS, Python, PHP, with dotnet in the works. Next are Ruby and Rust. I'd love community help adding support for more test frameworks and programming languages.

Here's feedback from an early user:

> This plugin is absolutely phenomenal and has become an indispensable part of my toolkit.

> It might sound strange, but I'm moving significantly faster on both new features and refactoring tasks now. The way it works in tandem with my strict ESLint setup is brilliant!I It iterates through issues and consistently produces clean, working code. It's not an exaggeration to say you've completely changed how I think about TDD and AI in my coding process due to this plugin.

Happy to answer questions!