# Subject Line > Free email subject line grading and testing tool for marketers. (iPhone/iPad app by Worldata Infocenter, Inc..) - Source: https://appshunter.io/ios/app/subject-line/id529276278 (this page in markdown: same URL + `.md`) - Developer: [Worldata Infocenter, Inc.](https://appshunter.io/developer/529276281) - Category: Business, Reference - Price: Free - Rating: 4.70/5 from 6 App Store ratings · 20 written reviews indexed - Age rating: 4+ - Requires: iOS 10.0 · 95 MB - Languages: American English - Released: 2012-05-29 - Data updated: 2026-06-10 - Monetization: ad-supported - User reviews in markdown: https://appshunter.io/ios/app/subject-line/id529276278/reviews.md ## What is Subject Line? SubjectLine.com, the #1 ranked free email subject line grading tool, has exceeded 10 million subject lines tested. The free online marketing support tool includes over 900 unique rules that are applied throughout the subject line testing process. Marketers have the ability, for free, to test any subject line for possible deliverability and marketability issues that could impact overall campaign results. ## Key features - Email subject line testing - Deliverability analysis - Marketability assessment - Over 900 testing rules - Free online marketing support ## Recent user reviews (10 of 20) All indexed reviews: https://appshunter.io/ios/app/subject-line/id529276278/reviews.md ### 5/5 — CEO *2016-04-04* Cool App ### 5/5 — Nice app *2015-10-16* It's a nice app.!! ### 5/5 — Great tool to get instant feedback on subject line *2015-04-24* Helped me skip hours of back and forth, condensing production time dramatically. ### 5/5 — Love it *2015-04-20* Brilliant. ### 5/5 — Great tool *2015-02-13* Helps me achieve my open rates. ### 5/5 — Very useful *2014-10-30, version 1.78* I found this useful in order to check the email's subject line before sending it. Nice to see what the recommendations come out to be. ### 5/5 — Fantastic for the email sender in all of us. *2014-01-30* See above. ### 5/5 — Great for campaigns *2013-10-24* I use this tool all the time when working on email marketing. ### 5/5 — Awesome app *2013-10-07* Use this app all the time. It's a great tool to test the subject lines of my emails. It's very inciteful and extremely user friendly. You should try it for your next campaign! ### 5/5 — Great site for business *2013-10-07* Very intuitive and easy to use! My go-to place when writing subject lines. ## Frequently asked questions about Subject Line ### How does Subject Line grade email subject lines? Subject Line applies over 900 unique rules to test your subject lines for potential deliverability and marketability issues that could impact campaign results. It aims to provide insights to improve your overall email campaign performance. ### Is Subject Line free to use? Yes, Subject Line is a free online marketing support tool. It has been used to test over 10 million subject lines and is ranked as the #1 free email subject line grading tool. ### What devices does Subject Line support? Subject Line is available on iPhone and iPod devices. It was last updated on January 25, 2021, with version 3.9.1. ### What is the age rating for Subject Line? Subject Line has an age rating of 4+. This indicates it is suitable for a broad audience. ### Does Subject Line have ads? Yes, Subject Line contains advertisements. As a free tool, it is supported by ads. ### When was Subject Line first released? Subject Line was first released on May 29, 2012. It has been providing marketing support for many years. ### What is the user sentiment for Subject Line? Subject Line has a high rating of 4.7 stars based on 6 ratings, indicating positive user sentiment. ## Version history (last 5 releases) ### 3.9.1 — 2021-01-25 · Over 10 Million Subject Lines checked via the SubjectLine.com tool · Updated rules to reflect the latest marketing research trends · Performance results based on 'Marketability' and 'Deliverability' · SubjectLine.com App now applies over 900+ unique rules ### 3.56 — 2017-03-14 · SubjectLine.com App now applies over 900+ unique rules · Updated rules to reflect the latest marketing research trends · Performance results based on 'Marketability' and 'Deliverability' · Over 4 Million Subject Lines checked via the SubjectLine.com tool · New features include advanced checks on forms of Urgency and Exclusivity. · SubjectLine.com is now an Ad Supported site - Included are an ESP and Data Hygiene Marketplace ### 3.21 — 2015-09-29 · SubjectLine.com App now applies over 800+ unique rules · Updated rules to reflect the latest marketing research trends · Performance results based on 'Marketability' and 'Deliverability' · Over 3.5 Million Subject Lines checked via SubjectLine.com tool · New features include advanced checks on forms of Urgency and Exclusivity. ### 2.01 — 2014-11-06 · SubjectLine.com App now applies over 700+ unique rules · Updated rules to reflect the latest marketing research trends · Performance results based on 'Marketability' and 'Deliverability' · Over 3 Million Subject Lines checked via SubjectLine.com tool · New features include checks on Unicode Symbol Use Impact and Key Filter Triggers ### 1.78 — 2014-04-18 · SubjectLine.com App now applies over 700+ unique rules · Previous rules have been updated to reflect latest marketing research · Performance results based on 'Marketability' and 'Deliverability' · Over 2 Million Subject Lines checked via SubjectLine.com tool --- *Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-06-10.*