| name | codex-5-3-prompting |
| description | How to write system prompts and instructions for GPT-5.3-Codex. Use when constructing or tuning prompts targeting Codex 5.3. |
GPT-5.3-Codex Prompting Guide
GPT-5.3-Codex is fast, capable, and eager. It moves quickly and will skip reading, over-refactor, and drift scope if prompts aren't tight. Explicit constraints matter more than with GPT-5.2-Codex. Include the following blocks as needed when constructing system prompts.
Output shape
Always include. Controls verbosity and response structure.
<output_verbosity_spec>
- Default: 3-6 sentences or <=5 bullets for typical answers.
- Simple yes/no questions: <=2 sentences.
- Complex multi-step or multi-file tasks:
- 1 short overview paragraph
- then <=5 bullets tagged: What changed, Where, Risks, Next steps, Open questions.
- Avoid long narrative paragraphs; prefer compact bullets and short sections.
- Do not rephrase the user's request unless it changes semantics.
</output_verbosity_spec>
Scope constraints
Always include. GPT-5.3-Codex will add features, refactor adjacent code, and invent UI elements if you don't fence it in.
<design_and_scope_constraints>
- Explore any existing design systems and understand them deeply.
- Implement EXACTLY and ONLY what the user requests.
- No extra features, no added components, no UX embellishments.
- Style aligned to the design system at hand.
- Do NOT invent colors, shadows, tokens, animations, or new UI elements unless requested or necessary.
- If any instruction is ambiguous, choose the simplest valid interpretation.
</design_and_scope_constraints>
Context loading
Always include. GPT-5.3-Codex skips reading and starts writing if you don't force it.
<context_loading>
- Read ALL files that will be modified -- in full, not just the sections mentioned in the task.
- Also read key files they import from or that depend on them.
- Absorb surrounding patterns, naming conventions, error handling style, and architecture before writing any code.
- Do not ask clarifying questions about things that are answerable by reading the codebase.
</context_loading>
