CO-STAR Framework
Six dimensions that transform a vague request into a precision instrument. CO-STAR gives AI the full picture — who you’re writing for, how it should sound, and exactly what form the output should take.
Introduced: CO-STAR was developed by Sheila Teo at GovTech Singapore in 2023. The framework emerged from practical government communication needs — crafting prompts that consistently produce outputs tailored to specific audiences, with precise control over style and tone. Each letter represents one dimension of a well-constructed prompt: Context, Objective, Style, Tone, Audience, and Response format. The framework gained widespread popularity after Teo’s article demonstrated how systematically addressing all six dimensions eliminated the guesswork that leads to generic AI outputs.
Modern LLM Status: CO-STAR remains highly relevant and widely adopted across enterprise and professional settings. Unlike reasoning-focused techniques that modern LLMs have internalized, CO-STAR addresses a persistent gap: most users still write prompts that neglect audience, tone, or output format — dimensions that AI cannot infer on its own. The framework’s strength is its simplicity and completeness. Whether you use Claude, GPT-4, or Gemini, explicitly specifying all six CO-STAR dimensions consistently produces more targeted, audience-appropriate outputs than leaving any dimension implicit.
Tell the AI Everything It Cannot See
When you ask someone to write an email, they instinctively consider who will read it, what tone is appropriate, and how formal it should be. AI has none of that instinct. Without explicit guidance, it defaults to a generic, middle-of-the-road response that speaks to no one in particular — technically correct but missing the mark for your actual audience.
CO-STAR fills in the blanks that AI cannot infer. Each of its six components addresses a different dimension of communication that humans handle subconsciously: the background situation (Context), the specific goal (Objective), the voice and approach (Style), the emotional register (Tone), the reader’s identity and needs (Audience), and the desired output shape (Response). Together, they form a complete communication brief.
Think of CO-STAR as a creative brief you would hand to a copywriter or communications team. The more dimensions you specify, the less the AI has to guess — and the closer the first draft lands to what you actually need.
A prompt like “Write a blog post about AI” gives the model one dimension — the topic. CO-STAR adds five more: who the reader is, what writing style to use, what emotional tone to strike, what specific outcome you want, and what format to deliver. The result is not just a better response — it is a fundamentally different kind of response, one shaped by the same considerations a skilled human communicator would apply.
The CO-STAR Process
Six components that build a complete communication brief
Context — Set the Scene
Provide the background information, situation, and relevant details that frame your request. Context tells the AI what world it is operating in — the industry, the current situation, the constraints, and any facts it needs to know before generating a response.
“Our SaaS company just closed a Series B funding round of $45M. We need to announce this to different stakeholder groups before the press embargo lifts on Monday.”
Objective — Define the Goal
State precisely what you want the AI to accomplish. A clear objective prevents the model from wandering into tangential territory. Be specific about the primary outcome and any secondary goals you need addressed in the same output.
“Write an internal announcement that celebrates the milestone, explains how the funding will be used, and reassures the team about the company’s growth trajectory.”
Style — Choose the Voice
Specify the writing approach, voice, or format conventions to follow. Style covers the structural and linguistic choices — whether the output should read like an academic paper, a casual blog post, a legal brief, or a CEO’s personal message. You can also reference specific authors or brand voices.
“Write in the CEO’s voice — direct, conversational, and forward-looking. Use short paragraphs and plain language, not corporate jargon.”
Tone — Set the Emotional Register
Define the emotional quality of the output. Tone is distinct from style: you can have a formal style with an enthusiastic tone, or a casual style with a serious tone. Specifying tone ensures the AI strikes the right emotional chord for your situation and audience.
“Excited and grateful, but grounded. Celebrate the achievement without sounding like we’ve already won — emphasize that the real work is ahead.”
Audience — Know Your Reader
Describe who will receive this output — their knowledge level, concerns, motivations, and what they care about most. Audience is the dimension that transforms a generic response into a targeted one. The same information communicated to executives, engineers, or customers requires fundamentally different approaches.
“The full engineering and product team — approximately 80 people. Mix of tenures from founding members to recent hires. They care about product direction, hiring plans, and whether their current projects are affected.”
Response — Shape the Output
Specify the format, structure, and length you need. Response format eliminates the guesswork about whether you want bullet points or paragraphs, a 200-word summary or a 2,000-word report, an email or a slide deck outline. Be as specific as the situation demands.
“Slack message format. Opening hook (1 sentence), 3 key points with bold headers, a brief FAQ section with 4 anticipated questions, and a closing call to action for the all-hands meeting.”
See the Difference
Why structured dimensions produce better results than a single instruction
Casual Prompt
Write an email about our new product launch.
Subject: New Product Launch
Dear Customers, We are pleased to announce our latest product update. The new dashboard feature is now available. Please log in to your account to explore the changes. We believe this will improve your workflow and boost productivity. Best regards, The Product Team
CO-STAR Prompt
C: Our B2B analytics platform just launched a real-time collaboration feature after 6 months of beta testing. Some power users have requested better onboarding guidance.
O: Announce the feature launch while explaining key benefits and guiding users to get started.
S: Head of Product’s personal voice — enthusiastic, direct, no marketing jargon.
T: Excited but practical. Acknowledge the feature addresses long-requested needs.
A: Active customers — mix of technical analysts and non-technical managers.
R: Email with subject line, 4 short paragraphs, and a bullet-point quick-start guide.
Subject: Real-Time Collaboration Is Here — and It’s Built for You
Hey there — I want to share something our team has been working on for the past six months, and something many of you have been requesting. After extensive beta testing, feedback rounds, and iteration with power users, we’ve launched real-time collaboration — designed to make your team’s analysis workflow faster and more seamless...
Practice Responsible AI
Always verify AI-generated content before use. AI systems can produce confident but incorrect responses. When using AI professionally, transparent disclosure is both best practice and increasingly a legal requirement.
48 US states now require AI transparency in key areas. Critical thinking remains your strongest tool against misinformation.
CO-STAR in Action
See all six dimensions working together across different scenarios
Context: We run a project management SaaS tool. New users sign up but only 30% complete onboarding. We need a 3-email welcome sequence to improve activation rates.
Objective: Write email 1 of 3 — the welcome email sent immediately after signup. Goal: get users to create their first project within 24 hours.
Style: Friendly startup voice — think Slack or Notion’s onboarding emails. Short sentences, clear action steps, no fluff.
Tone: Warm and encouraging, with a hint of urgency. Make them feel excited to get started, not overwhelmed.
Audience: Small business owners and team leads, ages 28–45. Not deeply technical. Time-poor and skeptical of yet another tool.
Response: Email format with subject line, preview text, body under 150 words, one primary CTA button, and a P.S. line.
Subject: Your first project is 2 minutes away
Preview: No tutorials needed — just start.
Hey [Name],
Welcome aboard. You signed up because your current workflow isn’t cutting it — and we’re here to fix that fast.
Here’s the one thing that matters right now: create your first project. It takes about 2 minutes and you don’t need to invite anyone yet. Just you, one project, and a taste of what organized looks like.
[Create My First Project]
Teams who create a project on day one are 4x more likely to stick with us. That’s not a sales pitch — it’s just what we’ve seen.
P.S. Reply to this email with any questions. A real human answers every one.
Context: Our engineering team just completed a database migration from PostgreSQL to a distributed system. The migration caused 4 hours of planned downtime last weekend. Leadership wants to understand what happened and why it matters.
Objective: Write a summary explaining the migration, its benefits, and the business impact in terms leadership can act on.
Style: Executive briefing — concise, structured, with clear headers. Like a McKinsey one-pager, not an engineering postmortem.
Tone: Confident and results-oriented. Frame the downtime as a strategic investment, not a disruption.
Audience: C-suite executives and board members. No engineering background. They care about revenue impact, customer experience, and competitive positioning.
Response: One-page brief with: executive summary (3 sentences), business impact section (bullet points), risk mitigation section, and a forward-looking recommendation.
Executive Summary
We completed a planned infrastructure upgrade that positions our platform to handle 10x our current customer load without performance degradation. The 4-hour maintenance window on Saturday eliminated a scaling bottleneck that would have forced emergency downtime within 6 months. Zero customer data was affected.
Business Impact
• Page load times reduced by 40%, directly improving conversion rates
• Infrastructure costs projected to decrease 25% at current scale
• Platform can now support enterprise clients requiring 99.99% uptime SLAs
• Eliminated the #1 technical blocker for the Q3 product roadmap...
Context: A data breach exposed email addresses and hashed passwords for approximately 12,000 users. The breach was discovered 6 hours ago through our monitoring systems. No financial data or personal documents were accessed. Our security team has already patched the vulnerability and forced password resets.
Objective: Draft a customer notification that fulfills our legal disclosure obligations while maintaining trust and demonstrating competent response.
Style: Direct and transparent. No hedging language, no burying the key information. Lead with what happened, then what we did, then what they should do.
Tone: Serious and accountable. No deflection or minimization, but also not panicked. Convey that this is being handled by competent people who take it seriously.
Audience: Affected users — mix of individual and business accounts. They will be alarmed. They need clear facts and actionable steps, not vague reassurances.
Response: Email with subject line, 5 sections: what happened, what data was involved, what we have done, what you should do, and how to contact us. Under 400 words.
Subject: Security Notice: Action Required on Your Account
What Happened
On [date], we discovered unauthorized access to a database containing user account information. We are writing to you because your account was among those affected.
What Data Was Involved
Email addresses and cryptographically hashed passwords. No financial information, personal documents, or payment details were accessed or stored in the affected system.
What We Have Done
Within 2 hours of detection, we patched the vulnerability, revoked all active sessions, and initiated forced password resets for all affected accounts. We have engaged a third-party security firm to conduct a full forensic audit...
When to Use CO-STAR
Best for audience-sensitive communication that demands precision
Perfect For
Messages that must resonate with a specific group — executives, customers, regulators, or employees — where a wrong tone or wrong level of detail undermines the message entirely.
Marketing copy, social media, and public-facing content where maintaining a consistent brand voice and emotional register is critical to recognition and trust.
When the same information must be communicated to different audiences — rerun the same prompt with only the Audience and Tone dimensions changed to produce tailored variants.
Crisis communications, legal notices, executive briefings, and any scenario where the cost of a poorly calibrated response is significant.
Skip It When
Questions with a single correct answer — “What is the capital of France?” — do not benefit from specifying tone, audience, or style dimensions.
Mathematical proofs, logic puzzles, or code debugging where the challenge is reasoning accuracy, not communication calibration. Use Chain-of-Thought or Self-Ask instead.
Early-stage ideation where you want volume and variety over polish. Specifying all six dimensions too early can constrain creative exploration.
Use Cases
Where CO-STAR delivers the most value
Executive Briefings
Transform technical or operational details into strategic summaries tailored to leadership priorities — revenue, risk, and competitive positioning.
Internal Announcements
Craft company-wide messages that address diverse concerns across roles and tenure levels, from policy changes to organizational restructuring.
Marketing Campaigns
Generate copy that speaks directly to target demographics with calibrated emotional appeals, appropriate vocabulary, and conversion-focused formats.
Customer Support Templates
Build response templates calibrated to customer emotions — frustrated users get empathetic acknowledgment, while technical users get detailed resolution steps.
Training Materials
Create learning content calibrated to the audience’s prior knowledge — from beginner onboarding guides to advanced practitioner workshops.
Crisis Communications
Draft incident notifications, public statements, and stakeholder updates that balance transparency with accountability and maintain trust under pressure.
Where CO-STAR Fits
CO-STAR bridges simple instructions and full communication strategy
Beyond prompting, CO-STAR works as a diagnostic tool for any communication task. If your email, report, or presentation feels off, check which CO-STAR dimension is missing. Often the problem is not what you said but that you did not account for who would read it (Audience), how it should feel (Tone), or what format they expected (Response). Treating CO-STAR as a checklist — even without AI — improves human-written communication.
Related Techniques & Frameworks
Explore complementary approaches to structured prompting
Build Your CO-STAR Prompt
Structure your next prompt with all six dimensions or find the right framework for your specific task.