Introducing Tenon Sentinel

The accessibility product market is flush with new overlays, each making newer, bolder, more bogus claims than the last, all while basically providing poor “fixes” and a UI widget that does nothing more than what users with disabilities already have on their computers.

So in July I sat down with a full list of Tenon’s 213 accessibility tests and made a list to answer: Which of these tests can be turned into a real fix? The answer: 74.

I then turned the result of that research into a script that can be injected on a customer’s site and, in practice, fixes 46% of automatically discoverable accessibility issues! That discovery lead to my exploration into what an ethical overlay would look like.

Meet Tenon Sentinel

The goal of Tenon Sentinel is to implement rapid, high-impact, and sustainable improvements to customer websites faster than any existing method and to provide key strategies for legal defense by addressing a number of the core arguments made by plaintiffs during lawsuit filings. Tenon Sentinel isn’t an overlay. It is a service that delivers real value by establishing the building blocks of a robust accessibility program.

Tenon Sentinel has the following core components:

  • Spline.js: Our automated repair script
  • A11y-POC: Our Accessibility Point-of-Contact service
  • Site Monitoring Service which includes both automated and manual testing
  • Accessibility Help Desk which allows our customers direct access to our bench of accessibility expert


Spline.js is a tool that automatically fixes over 800 distinct failure conditions on the customer’s website. The extent to which things get fixed depends largely on how bad the site is. In practice, we’re able to fix an average of 46% of accessibility issues with Spline.

These fixes include repairs to:

  • Tables
  • Images
  • Forms
  • Frames
  • Navigation
  • Document Structure
  • Media

Screen recording demonstrating hundreds of repairs on

As demonstrated in the gif above, Spline’s fixes are enabled on page load, with no need for the end user to trigger the fixes manually.  The fixes deployed by Spline are configurable by the customer. This has an immediate positive effect on the website without altering the site’s design or operation.

Real, verifiable repairs. Backed by data, not empty promises

To verify Spline’s effectiveness, I did a before & after by testing the homepages of 6379 sites that are existing overlay customers. The outcome for that before & after is listed below. 

The left & middle columns of the table show raw issue counts discovered before vs. after applying Spline.  The right column, however, shows the impact of the fixes.  As I stated above, Spline can fix 74 of errors discovered by Tenon’s 213 accessibility tests. However, in the real world, this results in an average of 46% of discovered issues being repaired.

Spline’s effectiveness, verified
  “Overlay A” After Spline Pct Fixed, After Spline
Min 2 1 1%
Max 2026 1239 100%
Mean 151 70 46%
Median 111 47 47%
Mode 4 23 50%


A11y-POC is a Point-of-Contact service that allows Tenon’s staff to be our customers’ front line in helping users who have accessibility challenges. This service satisfies one of the most common complaints in accessibility lawsuits. The POC presents a link on the customer’s site. A user can click that link that presents a form. The user can enter a message describing their concern which, on submission, gets sent to Tenon.

Tenon’s accessibility experts assess the issue(s) reported and investigate the cause of the issue. Tenon staff then liaise with the customer to inform them of what the problem is and how to fix the problem. Tenon staff also forward the information to our customer so that they can assist the end user in completing the task (i.e. a purchase) that the user had a problem with.

Screenshot of the A11y-POC lightbox. Appearance can be customized to match the customer's site.

The user interface for the POC also presents an accessibility statement for the customer as well as helpful links and tips for AT users, fulfilling yet another common complaint in accessibility lawsuits. If our customer does not have an accessibility statement, Tenon will help to create one.

Site Monitoring

Our Site Monitoring service has two components: Automatic and manual testing.

Automatic Monitoring

While the Spline.js script is excellent at fixing a large number of accessibility issues, there are others that can’t be fixed because they’re either too complex or would necessitate changes to design or operation. This is where ongoing automatic monitoring comes in. On a regularly scheduled basis, we test the customer’s site using Tenon. The results of this testing will be sent to the customer each month and will include reports like:

  • All new issues discovered this month
  • All issues repaired from the prior month
  • Duplicate issues discovered this month
  • A full list of issues.

The customer will also get an Executive Summary report in an accessible PDF document for sharing with stakeholders and executives.

Screenshot of TPM's Project Reports page, showing a summary of the month's data and links to download the content of the reports.

Manual testing

During each 12-month period, Tenon staff will do exhaustive manual testing of 10 components on the customer site. This manual testing is done with the same rigorous methodology of the audits we’ve done for customers like Intuit, Adobe, Bed Bath & Beyond, US Olympic Committee, and dozens of others. We will work with the customer to determine which components will be tested. Customers can schedule/ request these one-time tests at any time during the period.

Accessibility Help Desk

The final component of Tenon Sentinel is the Accessibility Help Desk. Tenon Sentinel customers will get access to Tenon’s bench of elite accessibility experts and will have the ability to ask any accessibility-related questions that they may have.


Give us a shout!


Call: +1 443.489.6549


Start your free trial of Tenon today!