Free instruction builder
Custom GPT Instructions & System Prompt Generator
Good Custom GPT instructions define the assistant’s role, objective, workflow, boundaries, and output format in language that can be tested. This browser-based builder turns a short use case into a structured instruction template you can review, edit, and copy without sending the form data to a server.
Last updated: July 19, 2026 · No sign-up · Runs in your browser
Describe the assistant
Generated instruction template
Review every section, remove unnecessary rules, and test with normal, ambiguous, and adversarial requests before relying on the template.
How to write reliable Custom GPT instructions
The builder separates persistent behavior from the user’s changing requests. It creates explicit sections for role, objective, audience, workflow, constraints, tone, and output format, then adds a clarification rule so the assistant does not silently invent missing requirements.
- 1. Define one primary job.State the recurring outcome instead of listing every possible task.
- 2. Make the workflow observable.Describe how the assistant should clarify, analyze, verify, and present work.
- 3. Separate behavior from knowledge.Instructions govern behavior; files and connected sources provide changing facts.
- 4. Test boundaries explicitly.Use cases with missing data, conflicting requests, and external side effects.
Primary references
- OpenAI: Creating a GPT — instructions define behavior, functions, and behaviors to avoid.
- OpenAI: Key guidelines for Custom GPT instructions — break complex workflows into explicit steps and trigger/instruction pairs.
Frequently asked questions
What should Custom GPT instructions include?
Include the assistant’s role, primary objective, intended audience, workflow, boundaries, preferred tone, output format, and what to do when information is missing. Keep tool permissions and uploaded knowledge separate from behavioral instructions.
Are Custom GPT instructions the same as a user prompt?
No. Instructions define persistent behavior and boundaries, while a user prompt supplies the current task or input. A good instruction set remains useful across many different user requests.
Does this generator send my text to an AI model?
No. The template is assembled locally in the browser with deterministic rules. Review the generated text before pasting it into any product or model.
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