--- title: Building MIRA With Codex: Lessons Beyond the Code description: A developer shares three lessons learned while building MIRA (an agentic tool) using OpenAI Codex, going beyond the initial v1.0.0 experience. Key takeaways:... canonical: https://daily.dev/posts/building-mira-with-codex-lessons-beyond-the-code-oeopsx2zl twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Building MIRA With Codex: Lessons Beyond the Code | daily.dev og:description: A developer shares three lessons learned while building MIRA (an agentic tool) using OpenAI Codex, going beyond the initial v1.0.0 experience. Key takeaways:... og:url: https://daily.dev/posts/building-mira-with-codex-lessons-beyond-the-code-oeopsx2zl og:image: https://api.daily.dev/og/posts/OEopSx2Zl.png og:image:alt: Building MIRA With Codex: Lessons Beyond the Code og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Building MIRA With Codex: Lessons Beyond the Code **[Medium](https://daily.dev/sources/medium_js)** · 5 min read · 0 upvotes · 0 comments ## Summary A developer shares three lessons learned while building MIRA (an agentic tool) using OpenAI Codex, going beyond the initial v1.0.0 experience. Key takeaways: prompts alone don't enforce agent behavior — capability restrictions (hiding tools, denying writes) are the real safety boundary; architectural decisions need explicit documentation (ARCHITECTURE_DECISIONS.md) because both the developer and the AI forget the reasoning behind code; and testing only in your own environment misses the new-user installation journey and error-recovery paths that real users expose. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [10 Lessons for Agentic Coding](https://daily.dev/posts/10-lessons-for-agentic-coding-k6iro6jit) · Hacker News · 0 upvotes · 0 comments - [Harness engineering: leveraging Codex in an agent-first world](https://daily.dev/posts/harness-engineering-leveraging-codex-in-an-agent-first-world-py6m8jwm4) · OpenAI · 1 upvotes · 0 comments - [OpenAI Begins Article Series on Codex CLI Internals](https://daily.dev/posts/openai-begins-article-series-on-codex-cli-internals-dwhoatisz) · InfoQ · 1 upvotes · 0 comments - [How OpenAI Codex Works](https://daily.dev/posts/how-openai-codex-works-ianegzsz8) · ByteByteGo · 5 upvotes · 0 comments - [Codex is powerful but this one setting made it far more useful for real-world projects](https://daily.dev/posts/codex-is-powerful-but-this-one-setting-made-it-far-more-useful-for-real-world-projects-t8awcf1dn) · XDA Developers · 0 upvotes · 0 comments --- Tags: [#testing](https://daily.dev/tags/testing), [#architecture](https://daily.dev/tags/architecture), [#ai-coding](https://daily.dev/tags/ai-coding), [#codex](https://daily.dev/tags/codex) [View this post on daily.dev](https://daily.dev/posts/building-mira-with-codex-lessons-beyond-the-code-oeopsx2zl) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Building MIRA With Codex: Lessons Beyond the Code","url":"https://daily.dev/posts/building-mira-with-codex-lessons-beyond-the-code-oeopsx2zl","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/building-mira-with-codex-lessons-beyond-the-code-oeopsx2zl"},"datePublished":"2026-07-21T17:12:52.759Z","dateModified":"2026-07-21T17:18:08.208Z","description":"A developer shares three lessons learned while building MIRA (an agentic tool) using OpenAI Codex, going beyond the initial v1.0.0 experience. Key takeaways:...","image":"https://media.daily.dev/image/upload/s--CxzD6vbw--/f_auto/v1722860399/public/Placeholder%2005","thumbnailUrl":"https://media.daily.dev/image/upload/s--CxzD6vbw--/f_auto/v1722860399/public/Placeholder%2005","isAccessibleForFree":true,"articleSection":"Medium","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Medium","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/medium","url":"https://daily.dev/sources/medium_js"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/building-mira-with-codex-lessons-beyond-the-code-oeopsx2zl","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"testing,architecture,ai-coding,codex","timeRequired":"PT5M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Medium","item":"https://daily.dev/sources/medium_js"},{"@type":"ListItem","position":3,"name":"Building MIRA With Codex: Lessons Beyond the Code"}]} ```