Paste your offer → scored subject-line pack
Paste your offer. Get 6–8 scored subject lines with length and spam-risk flags — then A/B in your ESP.
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Key Takeaways
- Ranked subject variants in seconds.
- Length + spam flags before you send.
- Honesty: not an open-rate guarantee or ESP.
Scored email subject packs for A/B
We do not send mail, warm domains, or guarantee inbox placement.
SubjectLab — definition
SubjectLab turns a pasted campaign brief into scored email subject-line variants with length and spam-risk flags so marketers can A/B without guessing in a blank ESP field.
What this is NOT
- Not an ESP, sender, or domain warmer.
- Not a promise of opens, clicks, or inbox placement.
- Not a substitute for ESP A/B and human review before send.
Controller / Processor — When packs mention privacy roles, we use GDPR Art.4 labels: Controller and Processor (decision-support only).
Good offer. Blank subject field.
Blank page
Each regulatory update can leave agent tools, data classes, and escalation paths out of sync.
One untested line
When the PDF lives apart from the agent runtime, blind spots show up in production.
Stacked spam words
Hand-editing checklists for every domain quietly drains engineering and compliance time.
Late A/B
Gaps often surface only after an audit, incident, or customer questionnaire.
Brief. Draft. Review.
Generator-style deliverables for agent governance — review with counsel before production.
Scored variants
Condition + action rules an agent runtime can evaluate.
Length score
Human-readable duties so owners see gaps before go-live.
Spam flags
Theme pointers for high-risk obligations — not conformity certification.
A/B checklist
Structured output you can wire into guardrails or middleware.
Everything you need for a subject pack
Built for platform and compliance teams who need enforceable checks without a learning curve.
6–8 scored variants
Condition + action rules an agent runtime can evaluate.
Length + spam flags
Human-readable duties so owners see gaps before go-live.
A/B checklist
Theme pointers for high-risk obligations — not conformity certification.
Copy-ready
Structured output you can wire into guardrails or middleware.
From brief to subject pack in 3 steps
Paste the brief
Paste company policy text and choose a domain (Finance, HR, Safety, General).
Generate
Create agent-callable checks plus a validation error list and framework themes.
Review
Export rules into your agent runtime; keep humans for exceptions and legal review.
Brief. Draft. Review.
Generator-style deliverables for agent governance — review with counsel before production.
Blank page
Each regulatory update can leave agent tools, data classes, and escalation paths out of sync.
Scored variants — Condition + action rules an agent runtime can evaluate.
Score · optional AI · human A/B
Deterministic length and spam-ish flags. Optional AI polish never claims open rates. You pick winners in your ESP — lab only, not an ESP.
Read the methodology →Subject lab — not an ESP
| # | SubjectLab | ESP / blank-box drafting |
|---|---|---|
| 1 | 6–8 ranked variants with flags | One untested line |
| 2 | Heuristic score + A/B checklist | Hope and send |
| 3 | Self-serve from $9/mo | Full ESP seat pricing |
| 4 | Decision-support only | May over-promise opens |
Methodology before you ship
AI draft · human review · decision-support only.
Read methodology →Open studioTry it on this page
or generate below.
Saved history
Built for people who A/B subjects
Capability cards describe what the studio scores. No fabricated open-rate claims.
A campaign brief becomes ranked subject lines.
Flags length_warn when lines run long for mobile.
Flags common spam-ish phrases — you still decide.
Simple plans that scale
All paid plans include
- Subject studio
- A/B checklist export
- Length + spam flags (decision-support)
- Email support on paid plans — no hidden add-ons for core studio use
- Limited AI drafts: 3/day · 15/mo (fair use)
- Studio demo (no extra LLM fee)
- AI included: 40 runs/day · 300/mo (fair use)
- No separate ChatGPT subscription required
- Priority support · 2 months free with yearly
Feature comparison
What each plan includes — quotas reflect the enforced fair use limits.
| Dimension | Free | Pro | Enterprise |
|---|---|---|---|
| Usage | |||
| AI runs | 3/day · 15/mo | 40/day · 300/mo | 200/day · 3,000/mo |
| Report export | Watermarked | Clean export | Clean export |
| Audit log | Not included | ✓ Included | ✓ Included |
| Product | |||
| 6–8 scored variants | ✓ Included | ✓ Included | ✓ Included |
| Length + spam flags | ✓ Included | ✓ Included | ✓ Included |
| A/B-ready checklist | ✓ Included | ✓ Included | ✓ Included |
| English-first drafts | ✓ Included | ✓ Included | ✓ Included |
| BYOK (your LLM key) | Not included | Not included | ✓ |
| SSO | Not included | Not included | Roadmap |
| Support & compliance | |||
| Support | Community | Priority | Custom SLA |
Already paid? Unlock Pro with your license
Licenses are issued manually after your payment is confirmed: we generate one per paid order and send it to the purchase email, typically within a few hours. Enter it below to activate Pro on this device — no account needed. Nothing yet? Write to lixingliangsy@163.com and reference your order email.
Your questions, answered
What does SubjectLab draft?
6–8 scored email subject variants with length and spam-risk flags — lab only, not an ESP.
Does this guarantee opens or inbox placement?
No. Scores are heuristics. You still A/B in your ESP and own deliverability.
Can I cancel anytime?
Yes. Self-serve plans cancel anytime; access continues until period end.
Do I need a credit card to start?
No. Start with email signup or Demo mode in the studio, then upgrade when ready.
Do I need my own ChatGPT / OpenAI subscription?
No for Free/Pro. AI runs are included in your plan (fair use) via our platform key. Enterprise can optionally bring your own OpenAI key (BYOK) — configure it at /settings (key stays server-side only).
What is Fair Use / what if I hit the AI limit?
Free includes 3 AI drafts/day and 15/month. Pro includes 40/day and 300/month. At the fair-use limit, Studio returns a labelled demo until reset — or use Enterprise BYOK for heavier volume.
Is checkout secure?
Payments are processed by Waffo Pancake (merchant of record).
What happens after I pay?
You receive access confirmation; fulfillment is tracked via webhook + order logs.
Quick answers
- 6–8 variants
- Length flags
- Spam-ish flags
- A/B-ready
- Pricing starts at $0 (Free).
More questions
What inputs?
Offer/brief, audience, goal, optional brand word.
Open-rate guarantee?
No. Heuristic scores only — not open-rate or inbox guarantees.
How many subjects?
Typically 6–8 ranked variants with flags — always review before send.
Demo or live?
Demo is labelled Rule-based; live polish needs a configured AI key.
Who is it for?
Indie marketers and founders who A/B subject lines before send.
Primary sources?
ESP subject-line length/spam guidance (Braze, Benchmark, GetResponse, Mailsoftly).
How it compares
| Dimension | Manual | SubjectLab |
|---|---|---|
| Speed | Hours to days | Minutes per run |
| Consistency | Varies by person | Same scoring pattern every run |
| Output | Free-form | Ranked subject pack + flags |
| Best for | Final sign-off | First-pass subject draft |
When not to use: Skip it when you need an ESP, warm-up, or legal CAN-SPAM counsel. This only scores subject drafts.
- Subject length and spam flags (2026) — From the SubjectLab blog.
- English-first email copy before locales — From the SubjectLab blog.
- Fleet launch notes — SubjectLab ships in the LX AI Micro-SaaS fleet.
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