What do on-page SEO tools check?

On-page SEO tools check the content, HTML elements and technical signals that help search engines understand and assess an individual webpage. They typically review keyword relevance, title tags, meta descriptions, headings, page structure, internal links, images, structured data and crawlability, then highlight issues that may limit visibility or create a poor user experience.

Keyword targeting and topical relevance

Most tools compare the page content with a target keyword or topic. They check whether the main subject is clear, whether important terms appear naturally in prominent areas and whether the content covers the information a visitor is likely to expect. This commonly includes reviewing the page title, introduction, headings, body copy, image alternatives and URL.

A useful tool should not encourage indiscriminate repetition of keywords. Excessive or unnatural use can make content difficult to read and may indicate that the page is being written for a formula rather than for its audience. Keyword checks are best treated as prompts to confirm relevance and coverage, not as instructions to insert a phrase wherever possible.

Page titles and meta descriptions

On-page tools check whether the title tag exists, is unique and accurately describes the page. They may also identify titles that are too short, excessively long, vague, duplicated across pages or missing the main subject. The title is an important relevance and search-result signal, so it should describe the page clearly rather than simply list keywords.

Meta descriptions are checked for presence, uniqueness, clarity and relevance. They do not directly determine rankings in the same way as the page content, but a well-written description can help searchers understand the result before visiting. Tools may flag descriptions that are duplicated, empty or unlikely to communicate the page’s purpose. Search engines can choose to display different text when another passage better matches a search.

Headings and content structure

Tools review the heading hierarchy to establish whether the page has a clear structure. They can identify missing headings, repeated headings, headings with no supporting content and heading levels used inconsistently. A clear main heading should describe the page, while subsequent headings should divide the content into logical sections.

Content checks may include readability, length, thin or sparse content, repeated wording and the use of related terms. These checks are useful for finding pages that do not fully answer their intended query, but automated assessments cannot determine quality reliably on their own. A shorter page may be appropriate for a specific task, while a longer page may still be unhelpful if it does not answer the reader’s needs.

URLs and canonical signals

An on-page audit can check whether the URL is present, accessible, descriptive and consistent with the page topic. It may flag unnecessarily complex URLs, excessive parameters, avoidable duplication or characters that make the address difficult to interpret.

Many tools also inspect the canonical tag. This tells search engines which version of substantially similar pages should be treated as the preferred URL. A missing, conflicting or incorrectly self-referencing canonical can create uncertainty, particularly where a site uses filters, tracking parameters, print versions or replicated content. Canonical tags are recommendations rather than a guarantee, so they should agree with internal links, redirects and the site’s wider architecture.

Internal and external links

Link checks identify broken links, redirects, pages with no internal links pointing to them and pages that contain unusually few or many links. They can also show whether important pages are reachable through a logical internal linking structure.

Internal links help users and crawlers discover related content and provide context through descriptive anchor text. Links should therefore be useful and specific, rather than relying repeatedly on generic wording. Tools may also inspect external links and their attributes, although the appropriate treatment depends on the relationship with the linked website and the purpose of the link.

Images and other media

Image checks commonly cover missing or unhelpful alternative text, oversized files, unsuitable formats, missing dimensions and slow-loading media. Alternative text should describe the image’s purpose for people who cannot see it; it should not be used to insert keywords. Decorative images generally need empty alternative text so assistive technology can ignore them.

Image dimensions and file sizes can affect page performance and layout stability. A tool may identify opportunities to compress images, use responsive versions or defer non-critical media. These recommendations should be tested against visual quality and accessibility requirements rather than applied automatically to every image.

Technical accessibility and crawlability

On-page SEO tools often check whether search engines can access and interpret the page. Typical checks include:

• HTTP status and redirect behaviour
• Robots directives, including the robots meta tag and, where relevant, the X-Robots-Tag response
• Whether important content is available in the rendered page
• Mobile presentation and viewport configuration
• Secure connections and mixed-content issues
• Structured data syntax and eligibility for relevant search features
• Page loading signals and other performance-related issues
• Duplicate or near-duplicate page content

These checks help distinguish a content problem from a technical delivery problem. For example, a well-optimised page cannot perform as intended if it returns an error, is blocked from crawling or is marked as unsuitable for indexing. A tool can identify the signal, but resolving it may require access to the CMS, server configuration, templates or development workflow.

Structured data and search appearance

Where structured data is used, tools can check whether the markup is valid, whether required properties are present and whether the selected type matches the visible content. Structured data can help search engines interpret entities such as products, organisations, articles, events or frequently asked questions, but it does not guarantee enhanced search-result features.

Markup must describe content that is genuinely present on the page. Adding inaccurate or hidden information can create quality and compliance issues. Validation should therefore be followed by a manual review of the page and the organisation’s wider implementation.

How to interpret an on-page SEO report

Reports usually separate errors, warnings and recommendations. An error often indicates a missing or blocking element, such as a broken page, inaccessible content or absent metadata. A warning may identify a potential weakness, such as a duplicated title or a page with limited internal links. A recommendation is generally an opportunity to improve clarity, relevance or performance rather than a strict requirement.

Prioritise findings according to their likely effect and the number of pages affected. Resolve access, indexing and template-level issues before spending time refining individual wording. Next, improve pages that are important to the business and already receive search demand or internal traffic. Finally, review lower-impact recommendations in context rather than trying to achieve a perfect tool score.

Automated checks are a starting point, not a substitute for judgement. Review the page as a user would: confirm that it answers the intended query, supports the next step, works on mobile devices, loads reliably and remains accessible. Search Console data, analytics, crawl reports and manual testing should be considered alongside the on-page score.

When used in this way, on-page SEO tools provide a repeatable quality check across individual pages and templates. They make omissions easier to find, give teams a consistent optimisation process and help separate practical improvements from recommendations that do not apply to the page.