---
title: "Put Your Own Logic Inside the Codex Agentic Loop"
url: https://daily.dev/posts/put-your-own-logic-inside-the-codex-agentic-loop-jowjgysff
source_url: https://towardsdatascience.com/put-your-own-logic-inside-the-codex-agentic-loop
type: article
source: "Towards Data Science"
published: 2026-08-24T18:26:40.864Z
updated: 2026-08-24T18:27:06.217Z
tags: ["python", "ai-agents", "prompt-engineering", "openai-codex"]
reading_time: 8
upvotes: 1
comments: 0
language: en
---

> ## Documentation Index
> Fetch the complete documentation index at: https://daily.dev/llms.txt
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# Put Your Own Logic Inside the Codex Agentic Loop

**[Towards Data Science](https://daily.dev/sources/tds)** · 8 min read · 1 upvotes · 0 comments

## Summary

A walkthrough of Codex hooks, a mechanism for attaching custom logic to lifecycle events like SessionStart, PreToolUse, PostToolUse, Stop, and SessionEnd during an agentic session. Hooks are configured with an event, a matcher, and a handler. A case study demonstrates using a Stop hook to enforce a quality gate on a deep-research task built with Codex, validating that a generated research brief contains enough sources and domain variety before the agent is allowed to finish, using a Python validation script and a hooks.json configuration.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://towardsdatascience.com/put-your-own-logic-inside-the-codex-agentic-loop>

## Questions this post answers

### How do I add a quality check that runs before Codex finishes a task?

Use a Stop hook, which runs after Codex prepares its final response but before it finishes. The hook receives the last_assistant_message as input, can run a validation script, and return a decision of block with a reason if checks fail, which sends feedback back to Codex to continue working within the same run rather than terminating it.

_Developers wiring quality gates into agent workflows can track Codex hook patterns like this on daily.dev._

### What are the different hook events available in Codex and when do they fire?

Codex emits five lifecycle events: SessionStart (session begins), PreToolUse (before a tool call), PostToolUse (after a tool finishes), Stop (when Codex is ready to finish its response), and SessionEnd (session ends). Each hook is configured with three components: the event, a matcher specifying conditions, and a handler defining the action to run.

_daily.dev helps developers building Codex agent workflows keep up with hook and lifecycle event patterns._

### Does Codex support matchers for the Stop event when configuring hooks?

No, Codex currently does not apply matchers to the Stop event, so a Stop hook configuration in hooks.json omits the matcher field entirely and simply defines the command to run whenever the Stop event fires.

_Teams customizing Codex hook configs can compare implementation quirks like this on daily.dev._

## Similar posts on daily.dev

- [How I use the same Git work log with Codex and ChatGPT](https://daily.dev/posts/how-i-use-the-same-git-work-log-with-codex-and-chatgpt-dncckvdht) · Flavio Copes · 0 upvotes · 0 comments

---

Tags: [#python](https://daily.dev/tags/python), [#ai-agents](https://daily.dev/tags/ai-agents), [#prompt-engineering](https://daily.dev/tags/prompt-engineering), [#openai-codex](https://daily.dev/tags/openai-codex)

[View this post on daily.dev](https://daily.dev/posts/put-your-own-logic-inside-the-codex-agentic-loop-jowjgysff)