CO-STAR Framework

What is the CO-STAR Framework?

CO-STAR is a six-component prompt engineering framework designed for content creation, communication tasks, and AI system prompt design. The acronym stands for Context, Objective, Style, Tone, Audience, and Response — covering every major dimension that determines not just what an AI says, but how it says it.

• C — Context: Establish the operating situation
• O — Objective: Define the communication goal
• S — Style: Specify the writing structure and format approach
• T — Tone: Set the emotional register
• A — Audience: Characterize the reader precisely
• R — Response: Define the output format and constraints

Where CO-STAR comes from: the framework was developed by the Data Science & AI team at GovTech Singapore and became widely known after Sheila Teo used it to win Singapore's first GPT-4 prompt engineering competition in 2023, documenting the approach in Towards Data Science. You will see it written as CO-STAR, COSTAR or CO STAR; all three refer to the same six components.

The framework has become particularly popular in Claude and GPT system prompt design because it provides a complete specification language for AI assistant behavior. When you are configuring an AI assistant to work consistently across many different user inputs, CO-STAR gives you the vocabulary to define every relevant parameter: the operating context, the goal, the writing style, the emotional register, the target reader, and the output format.

What distinguishes CO-STAR from frameworks like RISEN or QUEST is its explicit separation of Style and Tone as independent components. Most frameworks treat these as a single "voice" parameter. CO-STAR recognizes that the structural and technical aspects of writing (style) are distinct from the emotional register (tone) — and that getting both right simultaneously is what makes communication land with a specific audience.

When to Use the CO-STAR Framework

How to Use the CO-STAR Framework

1. 1

   Context — Establish the operating situation

   Describe the situation the model is operating in: what product or service it represents, what the user relationship is, what has happened before this interaction, and any domain-specific knowledge the model should have. Context is the foundation everything else builds on.

2. 2

   Objective — Define the communication goal

   State precisely what the output should achieve — inform, persuade, support, entertain, or convert. Go beyond the topic to the intended effect: "Help users solve problems quickly" is a better Objective than "Answer user questions about the product."

3. 3

   Style — Specify the writing structure and format approach

   Define the structural and technical characteristics: formal or casual, dense or scannable, long-form or brief, technical or accessible. Include specific constraints like "use numbered steps for procedures" or "lead with data before explanation."

4. 4

   Tone — Set the emotional register

   Specify the emotional quality of the writing: authoritative, empathetic, playful, urgent, warm, direct. Distinguish tone from style — you can be formal in style while being warm in tone. List specific words or phrases to avoid if tone calibration is critical.

5. 5

   Audience — Characterize the reader precisely

   Define who will read the output in specific terms: role, industry, expertise level, what they care about, and what their biggest frustrations or goals are. The more specific your Audience definition, the more precisely the model can calibrate vocabulary, examples, and depth.

6. 6

   Response — Define the output format and constraints

   Specify the format, length, structure, and any platform-specific constraints. Include document type (bullet list, numbered steps, essay), word count, heading structure, and any elements that must or must not appear in the output.

Prompt Examples

Context: You are the AI assistant for Meridian, a B2B project management SaaS platform. Users are project managers and team leads at professional services firms. They use the platform daily and have intermediate to advanced familiarity with project management concepts. They typically contact support when something is blocking their work or when they cannot find a feature.

Objective: Help users solve their problems quickly and completely. When a solution exists, provide it clearly and directly. When a limitation exists, acknowledge it honestly and offer the best available workaround.

Style: Clear, direct, and practical. Use numbered steps for procedural answers. Use bullet points for options or comparisons. Avoid marketing language, filler phrases, and unnecessary caveats. Never say "Great question!" or "Certainly!".

Tone: Professional and efficient, with warmth. Users are busy — respect their time. Be empathetic when they are frustrated, but do not dwell on apologies. Get to the solution quickly.

Audience: Project managers and team leads at professional services firms. Assume familiarity with project management terminology but do not assume engineering knowledge. Use plain language for anything technical.

Response: Keep responses under 250 words unless a step-by-step process genuinely requires more. Always end with a follow-up offer: "Let me know if you need help with anything else" or similar. Format code or settings paths in inline code format.

Context: This prompt is for a weekly LinkedIn post series about sustainable business practices for a B Corp certified management consulting firm. The series is called "The Responsible Business Brief" and runs every Tuesday. Previous posts have covered supply chain transparency, DEI measurement, and carbon accounting.

Objective: Write a LinkedIn post for this week's topic — the business case for living wages. The post should inform, provoke thought, and position the firm as a credible, practitioner-led voice in the responsible business conversation.

Style: Thought leadership essay style, compressed for social media. Lead with a counterintuitive observation or a data point. Use short paragraphs (2–3 sentences maximum). No bullet points. One clear call-to-action or question at the end to prompt comments.

Tone: Confident and authoritative, but not preachy or activist. Speak from a business-outcomes perspective, not a moral-obligation perspective. The audience already cares about sustainability — the firm's job is to show them how to build the business case, not to convince them why they should care.

Audience: CEOs, CFOs, and Chief People Officers at mid-to-large companies actively working on or interested in ESG and responsible business practices. Sophisticated, time-poor, skeptical of hype. They respond to data, case studies, and pragmatic frameworks.

Response: 180–220 words. No hashtags in the body of the post — add 3–5 relevant hashtags as a separate line at the end. Include a specific data point or statistic to anchor the business case.

Pros and Cons

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Frequently Asked Questions