Email on Acid vs Inbox Monster (2026): which should you pick?
As of Nov 13, 2026, Email on Acid grades higher than Inbox Monster: 1.8 against 1.4 out of 4.0.
Checked Nov 13, 2026 · graded Nov 13, 2026 by ToolGPA
Email on Acid grades higher on the free plan and platforms. They get the same grade on value for money, features and ease of use.
Price, platforms and features side by side. The table says where each price was read and when.
Email on Acid
Email previews and pre-send QA, now moving to Mailgun Inspect
Inbox Monster
Email rendering previews and inbox placement testing
Which one is for you
Pick Email on Acid if
- Fits if you check each campaign across many email clients
- Works for agencies that need unlimited users on one account
Look elsewhere if
- Pricey if you add it up, at $99 a month for 1,000 previews
- Skip it if you want accessibility or spam checks on the cheap plan, as they start at Premium, $199
- Watch out: the pricing page says customers move to Mailgun Inspect from June 2026 and old tests are not carried over
- Watch out: it does not send email, so you need a separate sending service
- Watch out: the trial length is not stated
Pick Inbox Monster if
- Fits if a design team checks every campaign on many devices and clients
- Works for enterprises that already budget for yearly software contracts
Look elsewhere if
- Skip it if you want to pay monthly, as every price is a yearly figure
- Pricey if you are one person, with the cheapest suite at $3,750 a year
- Too light for placement testing on the creative plans, which need the $15,000 deliverability suite
- Watch out: live device previews, translation and single sign-on need the Enterprise creative tier
- Watch out: there is no free plan or trial listed
How we grade them
| 1.8GPAEmail on AcidWeak | 1.4GPAInbox MonsterWeak | |
|---|---|---|
| Value for money | DBasic is $99 a month for 1,000 previews, above the category's dearer quarter ($49). The checks most people want sit on Premium at $199. | DCreative Essential starts at $3,750 a year, about $312 a month, against a dearest tenth that starts at $129 a month. The deliverability suite is $15,000. |
| Free plan and trial | DA free trial is offered, but the page states no length. | FNo free plan and no trial is listed on the pricing page. |
| Features | CPreviews, accessibility, link and image checks and spam analysis. It does not send email. | CPreviews on 120+ devices, QA checks, placement, DMARC monitoring and SMS testing, but each is its own suite with its own price. |
| Ease of use | CNo rating on record. Paste or send the email and read the results, with a migration to Mailgun Inspect under way. | CNo rating on record. Buying goes through sales, and rendering and placement tools need setup per account. |
| Platforms and integrations | BWeb, with an API and unlimited users on every plan and one listed integration. | CWeb only, with no integrations listed on the vendor pages. |
| Best for | previewing an email in many clients before a send | email design teams with a yearly budget |
The GPA is the average of the five grades: an A is 4 points, an F is none. The full reasons are on each tool's page: Email on Acid and Inbox Monster. How we grade
Price against what you get
Email on Acid starts at $99 a month and scores 2.3 out of 4 on features, ease of use and platforms. Inbox Monster starts at $312.50 a month when paid by the year and scores 2.0.
Email on Acid scores higher and starts $213.50 a month lower. Of the other email verification and deliverability tools on the chart, 8 score higher than Email on Acid for less, and 26 score higher than Inbox Monster for less.
Features, ease of use and platforms, averaged
What paid plans start at, a month (each step along is roughly double) →
- The best score at each price
- Has a free plan
- No free plan
Where they differ
- Inbox Monster also covers dMARC.
At a glance
| Email on Acid | Inbox Monster | |
|---|---|---|
| Pricing | Free trial | Paid |
| Starts at | $99 per month | $3,750 per year and up (creative suite) |
| Free plan | None | None |
| Free trial | Free trial offered; its length is not stated on the page | None listed |
| Web | ||
| Made by | Email on Acid | Inbox Monster |
| Price read from | emailonacid.com | inboxmonster.com |
| Checked | Nov 13, 2026 | Nov 13, 2026 |
Worth knowing
Email on Acid
- The pricing page says current customers will move to Mailgun Inspect from June 2026, and that old previews and tests are not carried over.
- Annual-plan customers migrate at the end of their current term.
- Basic has no accessibility, spam or link checks; those start at Premium.
- It does not send email; the FAQ says you need a separate sending service.
Inbox Monster
- Every price is a yearly starting figure, from $3,750 a year; there is no monthly or self-serve checkout.
- Creative, deliverability and SMS are sold as separate suites, each priced on its own.
- Live device previews, translation and single sign-on need the Enterprise creative tier.
- The deliverability suite lists professional services packages as an optional extra.
Key features
Email on Acid
- Client and device previews
- Each screenshot of a client or device counts as one preview, so a test across 50 clients uses 50 previews.
- Accessibility checks
- Premium tests are based on the W3C Web Content Accessibility Guidelines, which the vendor ties to the European Accessibility Act.
- Link and image validation
- Premium checks links and images in a message. The FAQ says these checks, unlike previews, are unlimited.
- Spam content analysis
- Premium includes content spam checks and HTML code analysis, judged on the message itself and not on your sending reputation.
- API access and unlimited users
- Every plan includes API access, and none of the plans limit how many people on a team can use the account.
Inbox Monster
- Email client previews
- The creative suite renders emails in more than 120 modern clients and devices, including dark mode, with team proofing.
- QA diagnostics
- Checks cover links, accessibility and click-through terms, and the Enterprise tier adds translation and approval workflows.
- Inbox placement and reputation
- The deliverability suite reports weighted inbox placement, spam-trap tests, reputation analysis and blocklist monitoring.
- DMARC monitoring and alerts
- The deliverability suite includes DMARC monitoring, real-time alerts and shareable custom reports for the team.
- SMS delivery testing
- A separate suite shows where text messages land by carrier, with link diagnostics and journey testing.
Plans
Email on Acid
Basic$99
per month for 1,000 previews
Unlimited users, 100+ preview clients and devices, API access; extra previews cost $0.15 each.
Premium$199
per month for 2,000 previews
Adds accessibility tests, HTML code analysis, link and image validation and spam content checks.
ContractCustom
Custom preview allotment with the Premium feature set and phone and chat support; sold through sales.
Inbox Monster
Creative Essential$3,750
per year and up, for 15,000 previews
120+ device renderings, QA and collaboration tools, AI summary previews, accessibility analysis and click map.
Creative Advanced$6,500
per year and up, for 30,000 previews
Same features as Essential with a higher preview allowance.
Creative Enterprise$10,000
per year and up, custom previews
Adds live device previews, translation, approvals, single sign-on, subaccounts and procurement support.
Deliverability suite$15,000
per year and up
Weighted inbox placement, reputation analysis, spam-trap testing, blocklist and DMARC monitoring, alerts and ESP integrations.
SMS suite$6,000
per year and up
Deliverability by carrier, virtualized previews, journey testing, link diagnostics and reputation checks.
Common questions
Which is cheaper, Email on Acid or Inbox Monster?
As of Nov 13, 2026, Email on Acid is cheaper to start with: $99 a month, against $312.50 a month when paid by the year for Inbox Monster. Email on Acid starts at $99 per month, and Inbox Monster starts at $3,750 per year and up (creative suite).
Which has a free plan, Email on Acid or Inbox Monster?
As of Nov 13, 2026, neither Email on Acid nor Inbox Monster has a free plan. Email on Acid has a free trial.
More comparisons
How this page was made
- The verdict at the top follows a fixed rule. When both tools are in the same category and either is in our top three for it, the verdict follows that ranking: the higher-placed tool is our pick. The top three weigh who each tool suits as well as its grades, so a pick can go against the GPA. Otherwise the page does not pick one and says which grades higher: the higher GPA first; on a tie, the one with a free plan, then the one that starts cheaper in dollars a month, counted the same way for both; if they are still level, what the choice depends on.
- The grades are our own, from each tool’s review or report card. The GPA is their average.
- Prices, plans and platforms come from each tool’s listing. The table above says where each price was read and when.
- The differences and the answers to the questions are worked out from those listings.