a21glossary for TYPO3

Organizations that need a glossary usually have an SEO problem

Explaining technical terms on a website sounds like a service feature. In reality, a21glossary solves a concrete technical problem: TYPO3 pages with content that requires explanation rank better when terms are internally linked, indexable as standalone pages, and instantly accessible via tooltips. The extension automatically generates links from a central term database throughout the content, without editors having to set each link manually.

For companies with specialist portals, knowledge platforms, or products that require explanation, a21glossary creates exactly the internal linking structure that Google interprets as topical authority. Instead of hiding 50 terms in an FAQ, 50 independent, indexable pages with Schema markup potential are created.

Typical use cases

Specialist portals with more than 100 terms. Industry associations, universities, and trade publishers maintain glossaries with hundreds of entries. a21glossary automatically links each term at its first mention in body text. For one client with 340 glossary entries, internal linking density increased by 28%, measurable through Google Search Console.

Product pages with technical vocabulary. Machine manufacturers, chemical companies, and medical device makers use specialized language that buyers and decision-makers do not always understand. A tooltip with 2-3 sentences of explanation keeps readers on the page instead of sending them to Google. Time on page increases, bounce rate decreases.

Multilingual knowledge platforms. Combined with TYPO3’s language handling, glossaries can be maintained per language. German terms link to German explanations, English to English. This works cleanly as long as the language configuration in TYPO3 is set up correctly.

Technical architecture

a21glossary works as a content post-processor. After TYPO3 renders a page, the extension scans the HTML output for defined terms and replaces them with linked variants. The terms themselves are stored in a dedicated database table and managed through a backend module.

The extension registers via a Content Object Post User Func hook in the TypoScript rendering process. This means it only intervenes after TYPO3 has fully rendered the content. As a result, it works independently of the content element type - whether Textmedia, News, or Custom Content Elements.

Tooltip display uses a small JavaScript snippet and CSS, both customizable. In modern TYPO3 setups, replacing the default JavaScript with a CSS-only solution is recommended to avoid impacting Core Web Vitals. Using the title attribute and a :hover selector, simple tooltips can be realized without a single line of JavaScript.

The glossary entries themselves are configurable via TypoScript: which pages should be scanned, how often a term may be linked per page (recommended: once), and which HTML areas are excluded (navigation, footer, other glossary entries).

Common problems and solutions

Performance degradation with large glossaries. From approximately 500 terms onward, the post-processing step can become noticeable, especially on text-heavy pages. The solution: activate caching. TYPO3’s page cache stores the result after the first rendering. Only when the cache is cleared does reprocessing occur. Additionally, reducing the term list to the actually used vocabulary helps - 200 precise terms outperform 800 including variants.

Incorrect links in headings and existing links. By default, a21glossary links everywhere, including within H2 tags or existing hyperlinks. This leads to nested links that are HTML-invalid. The TypoScript configuration allows excluding tags: excludeTags = h1,h2,h3,a,script. This setting belongs in every initial installation.

Conflicts with RealURL and routing. In older TYPO3 versions (before v9), issues arose when glossary detail pages were routed via RealURL. With TYPO3 v10+ and native Site Routing, this problem no longer exists. Anyone still using RealURL should migrate regardless.

Migration and version compatibility

a21glossary was originally developed for TYPO3 v4.x and updated over the years. The last actively maintained version in the TER supports TYPO3 v10 and v11. For TYPO3 v12, a community fork on GitHub ports the extension to the new TCA structure and changed hook system. For TYPO3 v13, no official version is available at this time.

Migration from v11 to v12 requires three adjustments: first, switching from $GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS'] to the new Event Dispatcher system; second, updating TCA definitions (wizard configuration); and third, adapting the TypoScript setup to the new Site Configuration.

Those planning for TYPO3 v13 face a decision: continue developing the community fork or switch to an alternative solution. One alternative is implementing the glossary functionality directly as a Custom Content Element with DataProcessor. The effort is approximately 2-3 developer days, the result is future-proof and independent of third-party maintenance. Gosign has performed this migration for multiple projects and can realistically estimate the actual effort based on an analysis of the existing glossary data.