How to Write Alt Text for Equation Images

First ask whether an image is necessary

If the equation can be published as structured text or MathML, prefer that. An image is appropriate when preserving a specific visual layout, exporting from a tool, or supporting a destination that cannot render structured mathematics.

Keep the editable equation source even when the delivered version is SVG or PNG.

Write alt text for a short equation

For a short standalone expression, state the equation in a readable order:

<img src="energy.svg" alt="E equals m c squared">

Include signs, grouping, exponents, and fractions. Do not describe colors, fonts, or the fact that it is an image unless those visual properties carry meaning.

Handle a complex derivation

A long proof or multi-line derivation usually exceeds a useful alt attribute. Use a concise alt value that identifies the content, then provide the full expression or explanation in visible nearby text.

<img src="derivation.svg" alt="Derivation of the quadratic formula; full steps follow">
<div class="equation-description">…complete readable derivation…</div>

This approach helps all readers and avoids an unmanageably long announcement.

Avoid duplicate announcements

If the exact equation is already present as accessible text next to the image, the image may be decorative and use an empty alt attribute. Confirm that hiding it does not remove unique annotations, highlighting, or spatial relationships.

A graph or geometric diagram is not equivalent to its equation alone. Describe the trend, axes, important points, and conclusion that the visual communicates.

Use consistent spoken terminology

Read symbols in the order required to reconstruct the expression. Say “less than or equal to,” “open parenthesis,” or “the quantity” when grouping could be ambiguous. Define unusual variables and conventions in the surrounding explanation.

Test the alternative

Navigate to the image with a screen reader and listen without looking at the graphic. Ask whether a reader can understand the same mathematical claim and whether the description is concise enough to follow. Also verify that the visible long description appears in the correct reading order.

Common mistakes

• alt="equation" or alt="math image".
• Copying raw LaTeX into alt text without considering how it will be spoken.
• Omitting a denominator boundary or radical scope.
• Repeating a full visible paragraph in the alt attribute.
• Treating a chart or diagram as if a formula alone described it.

Release checklist

Confirm that the image remains sharp when zoomed, has sufficient contrast, and is not the only source of essential information. Store the original LaTeX or MathML with the asset so the alternative can be corrected when the equation changes.

Test the accessible representation

For accessible equation images alt text, keep the visual equation and its semantic or textual alternative synchronized. Read the alternative without looking at the equation: it should preserve the relation, grouping, bounds, scripts, and variable names rather than listing isolated symbols.

Verification sequence

1. Navigate to the equation using only the keyboard.
2. Inspect the accessible name or MathML tree.
3. Listen with at least one screen-reader and browser combination available to the publishing team.
4. Recheck after conversion to PDF, image, presentation, or another content system.

When an image is unavoidable

Retain the editable source, provide a concise alternative for simple expressions, and add a longer adjacent explanation for equations whose structure cannot be expressed clearly in a short alt attribute.