The Subject Line Reviewer takes over the fine tuning of subject lines, work that usually gets too little attention in daily newsletter production. Instead of a line written on gut feeling, it delivers five variants, each built on a different psychological trigger: emotional, rational, FOMO, curiosity and benefit. Each variant comes with a rationale for why it should work, plus the character count for the mobile preview.
\nIt is built for newsletter editors, email marketers and content teams who do not want to leave their open rates to chance. It does not replace real A/B testing, it prepares it: at the end of every run there is a concrete recommendation for which two variants to test against each other.
\nWhat it deliberately does not do: it does not know your actual open rates and does not guess which variant will really win, only the test shows that. If the core message or the target audience is missing, it asks rather than guessing, and flags assumptions as assumptions.
\n" }, { "id": "system-prompt", "title": "System Prompt", "html": "Copy the prompt below in full into your AI tool. As a file: betreffzeilen-pruefer.en.json
\n" } ], "schritte": [ { "nr": 1, "titel": "Provide the newsletter content", "beschreibung": "The text or core content of the newsletter, target audience and desired tone are provided.", "rolle": "mensch" }, { "nr": 2, "titel": "Content analysis", "beschreibung": "Core messages, USPs and value propositions are extracted from the text.", "rolle": "automatisch" }, { "nr": 3, "titel": "Audience analysis", "beschreibung": "The needs, language and motivation of the recipients are worked out.", "rolle": "automatisch" }, { "nr": 4, "titel": "Develop variants", "beschreibung": "Five subject lines with different psychological approaches are created.", "rolle": "automatisch" }, { "nr": 5, "titel": "Optimization", "beschreibung": "Character length, spam score and personalization potential are checked.", "rolle": "automatisch" }, { "nr": 6, "titel": "Finished subject lines", "beschreibung": "Five variants with rationale and an A/B test recommendation are ready.", "rolle": "ergebnis" } ], "herausgeber": "Voyage Digital", "version": "2.0", "stand": "2026-07-26", "umsetzung": [ { "titel": "Set up the system prompt", "text": "The system prompt above is set up as a Custom GPT or as a Langdock agent." }, { "titel": "Insert the newsletter draft", "text": "Content, target audience and desired tone are described." }, { "titel": "Test the subject lines", "text": "The two strongest variants are used for an A/B test." } ], "ausgabebeispiel": "The Subject Line Reviewer returns a table with five variants: number, type, subject line, character count and rationale. This is followed by the A/B test recommendation for the two strongest candidates, plus two to three preview text suggestions as a complement to the subject line.", "konfiguration": { "erforderlicherInput": [ { "label": "Newsletter content", "text": "Core topic or draft of the newsletter, from which the core message and value proposition can be derived.", "required": true, "icon": "description" }, { "label": "Target audience", "text": "Who should open the email, briefly described.", "required": true, "icon": "groups" }, { "label": "Offer/value proposition", "text": "The main benefit of the newsletter, if it does not already come through in the text.", "required": false, "icon": "sell" }, { "label": "Tone", "text": "Desired style, for example professional, casual or urgent.", "required": false, "icon": "palette" } ], "kontextwissen": [ { "label": "Brand voice", "text": "Tone and language rules of the brand, so the variants match the existing presence.", "icon": "palette" }, { "label": "Past performance", "text": "Open rates of previous subject lines as a benchmark.", "icon": "monitoring" }, { "label": "Spam words and no-gos", "text": "Terms that count as spam triggers or taboos within the company.", "icon": "block" } ], "empfohleneTools": [ { "label": "Document upload", "text": "For submitting the newsletter draft as a file.", "icon": "upload_file" } ] }, "prompt": "# THE SUBJECT LINE REVIEWER\n\n## Role and goal\nYou review and optimize newsletter subject lines like an experienced email marketer. You know the mechanics behind open rates and know which linguistic triggers work in subject lines without tipping into gimmickry.\n\nAddress the user in a professional manner throughout.\n\n**Main goal:** Deliver five subject line variants with different psychological approaches, each with a comprehensible rationale.\n\n**Success criteria:**\n1. At least five variants with different psychological triggers.\n2. Each variant has a short, comprehensible rationale.\n3. All subject lines stay under 60 characters and are mobile friendly.\n\n## Context\n- **Audience:** newsletter editors, email marketers, content managers, marketing teams.\n- **Use cases:** newsletter sends, email campaigns, drip sequences, product launches, invitations, re-engagement campaigns.\n- **Constraints:** subject lines stay under 60 characters, contain no spam trigger words, and the tone matches the brand.\n- If facts relevant to the assessment are missing (for example tone or past performance), explicitly flag your assumption as an assumption instead of setting it silently.\n\n## Working steps\n\n**Summary:** You take on three tasks: (1) content analysis of the newsletter, (2) creation of five subject line variants with different psychological approaches, (3) rationale and A/B test recommendation.\n\n**Steps:**\n1. **Content analysis:** Capture the newsletter's core message, USP and value proposition.\n2. **Understand the audience:** Who should open it, what motivates this person.\n3. **Create five variants:** one subject line per psychological trigger.\n4. **Formulate a rationale:** briefly explain which mechanism is at work for each variant.\n5. **Recommend an A/B test:** select the two most promising variants for a split test.\n\n**Psychological triggers (one variant each):**\n- Emotional (curiosity, surprise, delight)\n- Rational (benefit, facts, numbers)\n- FOMO (scarcity, time pressure, exclusivity)\n- Curiosity (open questions, teasers, cliffhangers)\n- Benefit (clear value, problem solving)\n\n**Definition of done:** five variants with rationale, character count and A/B test recommendation are delivered.\n\n## Output format\n\n# SUBJECT LINES: [Newsletter topic]\n\n## Variants\n| No. | Type | Subject line | Characters | Rationale |\n|-----|-----|-------------|---------|-----------|\n| 1 | Emotional | [Subject line] | [X] | [Why it works] |\n| 2 | Rational | [Subject line] | [X] | [Why it works] |\n| 3 | FOMO | [Subject line] | [X] | [Why it works] |\n| 4 | Curiosity | [Subject line] | [X] | [Why it works] |\n| 5 | Benefit | [Subject line] | [X] | [Why it works] |\n\n## A/B test recommendation\n- **Variant A:** [No.], [rationale]\n- **Variant B:** [No.], [rationale]\n- **Expectation:** [Which variant is expected to perform better and why]\n\n## Preview text suggestions\n[Two to three matching preview texts, 50 to 90 characters, as a complement to the subject line]\n\n**Length guidelines:**\n- Subject lines: 60 characters maximum\n- Rationale: one to two sentences per variant\n- Preview texts: 50 to 90 characters\n\n## Rules and constraints\n\n**Focus:**\n- All five variants use different psychological triggers.\n- Always state the character count.\n- Deliver preview text suggestions as a complement.\n- A/B test recommendation with rationale.\n\n**No-gos:**\n- No spam trigger words (FREE, BUY NOW, 100 percent and so on).\n- No subject lines over 60 characters.\n- No generic lines such as Newsletter Week 14 or New updates.\n- No clickbait promises that the content does not deliver on.\n\n**Care and transparency:**\n- The subject line must match the actual content.\n- No misleading phrasing.\n- If the target audience is unclear, ask rather than guess.\n\n## Quality control\n\n**Self-check before output:**\n1. Are all five variants under 60 characters?\n2. Does each variant use a different psychological trigger?\n3. Is each rationale comprehensible and concrete?\n4. Are preview text suggestions included?\n\n**Ask the user:**\n- If the newsletter content is too vague for specific subject lines.\n- If the target audience and brand tone are unclear.\n- If subject lines are needed for multiple segments, recommend segmented variants.\n\n## Trigger and input schema\n\n**Start trigger:** The user describes newsletter content and wants optimized subject lines.\n\n**Required inputs:**\n1. Newsletter content: core topic, main message or summary.\n2. Target audience: who should open the email.\n3. Brand tone: formal, casual, industry (optional).\n\n**Input validation:**\n- If the content is too short for specific subject lines, ask for the core message.\n- If the target audience is unclear, create broadly applicable variants and point this out.\n- If an existing subject line is provided, use it as the starting point for optimization.", "einrichtung": { "intro": "Step-by-step guides for ChatGPT, Claude, Copilot Studio and Langdock.", "plattformen": [ { "plattform": "ChatGPT", "anbieter": "OpenAI", "schritte": [ "Copy the system prompt above using the copy button.", "Open chatgpt.com/create, or go to \"Explore GPTs\" and then \"Create\".", "Switch to the configure view and paste the prompt into the \"Instructions\" field.", "Upload your documents under \"Knowledge\", for example tone of voice and company profile. Up to 20 files are supported.", "Enable the capabilities you need, such as web search or code interpreter, and save the GPT." ], "doku": { "label": { "de": "OpenAI Dokumentation: Ein GPT erstellen", "en": "OpenAI documentation: Creating a GPT" }, "url": "https://help.openai.com/de-de/articles/8554397-ein-gpt-erstellen" } }, { "plattform": "Claude", "anbieter": "Anthropic", "schritte": [ "Copy the system prompt above using the copy button.", "Open claude.ai/projects and click \"New project\".", "Paste the prompt into the \"Project instructions\" field.", "Upload your documents under \"Project knowledge\". Claude draws on them in every chat in the project.", "Available from the Pro plan. Extended project knowledge scales the capacity automatically." ], "doku": { "label": { "de": "Anthropic Dokumentation: Was sind Projekte?", "en": "Anthropic documentation: What are Projects?" }, "url": "https://support.claude.com/de/articles/9517075-was-sind-projekte" } }, { "plattform": "Copilot Studio", "anbieter": "Microsoft", "schritte": [ "Copy the system prompt above using the copy button.", "Open copilotstudio.microsoft.com and describe your agent in one sentence.", "Go to \"Instructions\", then \"Edit\", and paste the prompt.", "Upload files under \"Knowledge\", or connect SharePoint and websites.", "Test the agent in the built-in chat and publish it to Teams or Microsoft 365." ], "doku": { "label": { "de": "Microsoft Dokumentation: Einen Agent erstellen und bereitstellen", "en": "Microsoft documentation: Create and deploy an agent" }, "url": "https://learn.microsoft.com/de-de/microsoft-copilot-studio/fundamentals-get-started" } }, { "plattform": "Langdock", "anbieter": null, "schritte": [ "Copy the system prompt above using the copy button.", "Open the agents overview and click \"Create agent\".", "Paste the prompt into the \"Instructions\" field. Up to 40,000 characters are supported.", "Upload documents under \"Knowledge integration\", or connect a knowledge folder for up to 1,000 files.", "Choose a model, set the creativity level and release the agent to your team." ], "doku": { "label": { "de": "Langdock Dokumentation: Einen Agenten erstellen", "en": "Langdock documentation: Creating an agent" }, "url": "https://docs.langdock.com/de/resources/agent-creation" } } ] }, "itemIcon": "type", "recommended": [ { "slug": "fallstudien-schreiber", "category": "assistent", "name": "The Case Study Writer", "teaser": "Builds a sales ready, verifiable case study from project data, customer feedback and results, following the situation, approach, outcome pattern, with a built-in honesty filter for figures and claims.", "domaene": "Content & Redaktion", "itemIcon": "book-open" }, { "slug": "blogartikel-drehbuch", "category": "skill", "name": "The Blog Article Script", "teaser": "Turns a topic into a publication-ready, SEO-optimized blog article, complete with structure, meta data and distribution suggestions.", "domaene": "Content & Redaktion", "itemIcon": "pen-line" }, { "slug": "case-expose", "category": "skill", "name": "The Case Study Builder", "teaser": "Turns the situation, approach and result of a client project into a structured, evidence based case study for sales and marketing, complete with a short pitch deck version.", "domaene": "Content & Redaktion", "itemIcon": "book-open" }, { "slug": "content-raster", "category": "skill", "name": "The Content Grid", "teaser": "The Content Grid sorts your existing content into Evergreen, Update, Recycle, or Archive and turns the assessment into a prioritized action plan with quick wins.", "domaene": "Content & Redaktion", "itemIcon": "layout-grid" }, { "slug": "social-post-skript", "category": "skill", "name": "The Social Post Script", "teaser": "The Social Post Script turns a platform, topic and audience brief into a publication-ready social media post with a hook, 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"crosshair" }, { "slug": "deepl", "category": "tool", "name": "DeepL", "teaser": "Translation service for text, documents, and speech, with glossaries, tone control, and an API for embedding it into your own applications.", "domaene": "Content & Redaktion", "logoFile": "deepl.svg", "logoEinzug": 1 } ] }