If you teach on Canvas, you have an Ally score. It shows up as a little gauge next to every piece of content you upload — green, amber, or red. Your department might track it. Your admin definitely tracks it. But Ally gives you a number without really explaining what that number measures.
That matters because knowing what Ally checks lets you fix the things that actually move your score, instead of guessing your way through the feedback panel. Here is the full breakdown: all nine checks, what triggers each one, and how much weight it carries.
How the score works
Ally does not score your course as a single unit. It scores each piece of content individually on a 0–100% scale, then averages those scores across everything in the course. A Canvas page with proper headings and alt text might score 100%. An untagged PDF scores 0%.
The consequence is simple and brutal: one bad file can drag down an otherwise clean course. If you have 20 items scoring 100% and a single untagged PDF scoring 0%, your course average drops to roughly 95%. Upload five untagged PDFs and you are looking at 80% — amber territory — even though everything else is perfect.
This is why understanding the individual checks matters. Some checks apply to every piece of content. Others only apply to specific file types. Knowing which is which lets you prioritize.
The 9 checks
Ally evaluates your content against nine accessibility criteria. Not every check applies to every file — a Canvas page will not be checked for PowerPoint reading order, for example — but here is what each one looks for.
1. Images without alt text
Every <img> tag in your Canvas pages, and every image embedded in uploaded documents, needs a text description. Screen readers rely on this alt text to convey what the image shows. A decorative border can be marked as decorative (empty alt attribute), but a chart, diagram, or photograph of a historical document needs a real description.
What triggers it: Any image element missing the alt attribute, or with an empty alt on a non-decorative image. This includes images pasted directly into the Canvas rich text editor.
2. Untagged PDFs
This is the single biggest score killer in most courses. PDFs need internal structure tags — headings, paragraphs, lists, figures with alt text — so screen readers can navigate them. A “tagged” PDF has this structure baked in. An untagged PDF is effectively a flat image of text to assistive technology, even if it looks perfectly fine on screen.
What triggers it: Any PDF that lacks a tag tree. This includes most PDFs created by “printing to PDF” from Word, scanning documents, or exporting from applications that do not support tagged PDF output. An untagged PDF scores 0% automatically — there is no partial credit.
3. Broken heading hierarchy
Headings need to follow a logical order. If your page starts with an H1, the next heading should be H2, not H4. Skipping heading levels confuses screen reader users because they navigate pages by jumping between headings — a missing H2 makes it sound like content was removed.
What triggers it: Any heading level that skips one or more levels. Going from H1 straight to H3, or from H2 to H5. Going from H3 back up to H2 is fine — Ally only flags downward skips.
4. Low color contrast
Text needs enough contrast against its background to be readable by people with low vision or color blindness. WCAG 2.1 AA requires a contrast ratio of at least 4.5:1 for normal-sized text and 3:1 for large text (18px bold or 24px regular). Light gray text on a white background is the most common offender.
What triggers it: Any text element where the foreground-to-background contrast ratio falls below 4.5:1. This is checked in Canvas pages and HTML files. Ally analyzes the computed colors, so it catches issues even when the contrast looks “close enough” to the eye.
5. Tables without headers
Data tables need their first row (or column) marked as header cells using <th> tags, not just bold text in regular <td> cells. Without proper headers, a screen reader reads table data as a flat list of values with no indication of what each value represents.
What triggers it: Any HTML table where the first row uses <td> instead of <th> elements, or tables that lack a <thead> section entirely. This applies to tables in Canvas pages, HTML files, Word documents, and PDFs.
6. Vague link text
Links that say “click here,” “read more,” or “link” do not tell screen reader users where the link goes. Screen readers can pull up a list of all links on a page, and a list of five items that all say “click here” is useless. Link text should describe the destination: “download the syllabus (PDF)” instead of “click here.”
What triggers it: Links whose visible text is generic — “click here,” “here,” “read more,” “more,” “link,” or a raw URL used as display text. Ally maintains a list of common vague phrases and flags any match.
7. Missing iframe/embed titles
When you embed a YouTube video, a Google Form, or any external tool using an <iframe>, that element needs a title attribute. The title tells screen reader users what the embedded content is before they decide to interact with it — for example, “Lecture 4: Intro to Thermodynamics (YouTube video).”
What triggers it: Any <iframe> or <embed> element that is missing the title attribute, or where the title is empty. This is common with videos pasted into the Canvas editor using embed codes from YouTube or Vimeo.
8. PowerPoint accessibility
Ally checks .pptx files for three things: whether every slide has a title, whether images have alt text, and whether the reading order on each slide is logical. Reading order is the sequence a screen reader follows when reading the slide — it is set in PowerPoint’s Selection Pane and is often wrong by default, especially when you move elements around after creating them.
What triggers it: Missing slide titles, images without alt text descriptions, or a reading order that does not match the visual layout. PowerPoint files with multiple violations can score very low because each issue compounds across every slide in the deck.
9. Word document accessibility
Ally checks .docx files for proper use of heading styles (not just bold text resized to look like a heading), image alt text, and table structure. A Word document that uses “Normal” style for everything and relies on font size and bold to create visual hierarchy will fail the heading check entirely.
What triggers it: Documents that lack built-in heading styles, contain images without alt text, or include tables without designated header rows. Like PDFs and PowerPoints, Word documents are scored as individual content items, so a single badly structured .docx lowers your course average.
Which checks matter most
Not all nine checks carry equal weight in practice. Here is a rough ranking by how much each one typically affects your overall course score:
- Untagged PDFs — by far the biggest score killer. A single untagged PDF scores 0% and most courses have several. This is where the largest gains come from.
- Images without alt text — high frequency. Every content page, every document. These add up fast.
- Word and PowerPoint accessibility — these files are scored as complete items. A 40-slide deck with no slide titles will score very low and count as one item pulling down the average.
- Broken heading hierarchy — common in longer Canvas pages. Usually a quick fix once you see the structure.
- Tables without headers — less frequent but an easy fix in the Canvas editor.
- Low color contrast — easy to fix once identified. Change your text colors to meet the 4.5:1 ratio.
- Vague link text — the easiest win. Find every “click here” and rewrite it. Takes minutes.
- Missing iframe titles — simple one-line fix per embed. Low frequency in most courses.
The pattern is clear: fix your PDFs first, then your images, then your Office documents. Those three categories account for the vast majority of score impact. The remaining checks — contrast, link text, headings, tables, iframes — are easier and faster to fix, but they move the needle less.
What to do next
Now that you know what Ally is actually measuring, you can stop guessing and start prioritizing. Focus on the checks that carry the most weight, fix them in order, and watch your score climb.
For a step-by-step walkthrough, read How to Fix Your Ally Score in Canvas. It covers the exact workflow for addressing each of these checks, from the highest-impact fixes to the quick wins you can knock out in an afternoon.
Or, if you would rather automate the process, download FixAllyScore and let it handle the remediation for you. It runs on your machine, processes your files locally, and addresses all nine checks automatically.
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