The SEO Agency Checklist: How to Diagnose Site Health, Run Technical Audits, and Drive Performance Growth

You’ve hired an SEO agency, or you’re about to. The pitch deck was slick, the case studies were impressive, and the promise of “more traffic” felt like music to your ears. But here’s the uncomfortable truth: not all SEO agencies deliver the same results, and the difference between a partner who moves the needle and one who just moves your budget often comes down to one thing—technical rigor.

Search engines don’t care about your brand story if your site takes eight seconds to load, serves duplicate content across fifty URLs, or blocks Googlebot with a misconfigured `robots.txt`. This is where technical SEO and site health become the foundation of any sustainable growth strategy. In this guide, we’ll walk through a practical checklist for vetting an SEO agency’s technical capabilities, running your own site audit, and understanding the risks that come with shortcuts like black-hat links or poorly implemented redirects.

Step 1: Start with Crawlability and Budget

Before any keyword research or content strategy can work, search engines need to find your pages. Crawl budget—the number of URLs a search engine like Google will crawl on your site within a given timeframe—is a finite resource. If your site has thousands of orphaned pages, infinite filter parameters, or a bloated sitemap, you’re wasting that budget on junk instead of your high-value content.

What to check with your agency:

• Does your `robots.txt` file accidentally disallow important resources like CSS or JavaScript? A single misplaced `Disallow: /` can hide your entire site.
• Is your XML sitemap up to date, and does it only include canonical URLs? Avoid listing paginated pages or session IDs.
• Are you monitoring crawl stats in Google Search Console? A sudden drop in crawled pages often signals a technical issue like a server error or a directive change.

A competent agency will audit your crawl budget as part of their initial technical SEO audit. If they skip this step, they’re likely missing half the picture.

Step 2: Audit Core Web Vitals and Site Performance

Core Web Vitals—Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS)—are now ranking signals. But more importantly, they’re user experience signals. A slow site doesn’t just hurt your rankings; it hurts conversions. Imagine a potential customer landing on your product page, only to watch a hero image load for four seconds while the “Add to Cart” button shifts down the page. They leave. You lose the sale.

Practical audit steps:

1. Run your site through Google’s PageSpeed Insights or Lighthouse. Focus on mobile scores first—most traffic comes from mobile devices.
2. Identify the biggest contributors to poor LCP: oversized images, slow server response times, or render-blocking JavaScript.
3. For CLS, check if ad slots, images, or embeds lack explicit width and height attributes. Even a single layout shift can tank your score.
4. For FID/INP (Interaction to Next Paint), look for long tasks caused by heavy JavaScript frameworks or third-party scripts.

Poor Core Web Vitals are often a symptom of deeper technical debt. An agency that offers to “fix” them with a quick plugin or a CDN without understanding the root cause is selling a band-aid, not a solution.

Step 3: Tackle Duplicate Content and Canonicalization

Duplicate content isn’t a penalty in the traditional sense, but it dilutes your ranking potential. If two pages have the same or very similar content, search engines don’t know which one to prioritize. The result? Neither ranks well.

The canonical tag (`rel="canonical"`) is your tool for telling search engines which version is the master copy. But it’s often misused. Common mistakes include:

• Setting canonical tags to URLs that return 404 errors.
• Using canonical tags on paginated series (e.g., category pages) instead of implementing `rel="next"` and `rel="prev"`.
• Forgetting to self-reference canonicals, meaning Page A points to Page B, but Page B doesn’t point back.

A thorough technical SEO audit will identify all instances of duplicate content—whether from URL parameters, printer-friendly versions, or HTTP/HTTPS mixed content—and recommend a clear canonicalization strategy. If your agency tells you “duplicate content isn’t a problem,” ask them to show you the data.

Table: Common Technical SEO Issues and Their Impact

Step 4: Evaluate On-Page Optimization and Intent Mapping

On-page optimization goes beyond stuffing keywords into title tags. Modern SEO requires mapping content to search intent: what is the user actually trying to accomplish? A query like “best running shoes” implies comparison and purchase intent, while “how to tie running shoes” is informational. Serving a product page for the latter will fail, no matter how well-optimized the meta description is.

What a strong agency does:

• Conducts keyword research with intent segmentation, separating transactional, informational, and navigational queries.
• Creates content clusters that link related topics together, building topical authority.
• Optimizes for featured snippets by structuring content with clear headings, bullet points, and direct answers.

If your agency hands you a list of high-volume keywords without discussing intent or user journey, they’re operating on outdated tactics.

Step 5: Build a Link Profile That Lasts

Link building remains a critical ranking factor, but the era of black-hat link schemes—private blog networks (PBNs), paid links, automated directory submissions—is over. Search engines have gotten better at detecting unnatural patterns. A single link from a spammy domain can trigger a manual action, and recovery is painful.

Risk-aware link building checklist:

• Never buy links from link farms or PBNs. The short-term traffic gain isn’t worth the long-term penalty risk.
• Focus on editorial links from reputable sites in your industry. This requires genuine outreach and valuable content.
• Audit your backlink profile regularly using tools like Ahrefs or Majestic. Look for sudden spikes in low-quality links, which could indicate negative SEO from competitors.
• Understand metrics like Domain Authority (DA) and Trust Flow (TF) as relative indicators, not absolute guarantees. A high DA site with zero topical relevance won’t help your niche.

An agency that promises “100 high-DA backlinks in 30 days” is either lying or using black-hat methods. Sustainable link building is slow, deliberate, and transparent.

Step 6: Connect Technical SEO with Accessibility

There’s a growing overlap between technical SEO and web accessibility. Properly implemented aria-labels, descriptive image alt text, and semantic HTML structure help both search engines and users with disabilities understand your content. For example, an `aria-label` on a navigation button tells screen readers what the button does, and Google uses that same signal to understand page context.

Key areas to check:

• Image alt text: Every meaningful image should have descriptive alt text. Decorative images can use `alt=""` to be ignored by screen readers.
• Heading hierarchy: Use a single `H1` per page, followed by logical `H2`, `H3` structure. Skipping levels confuses both users and crawlers.
• Keyboard navigation: Ensure all interactive elements are reachable via keyboard. If a dropdown menu can’t be opened with the Tab key, it’s an accessibility failure.

For a deeper dive, see our guides on accessibility and SEO overlap and WCAG content best practices.

Step 7: Monitor, Report, and Iterate

Technical SEO is not a one-time fix. Sites change—new pages are added, plugins update, redirects break. A reliable agency provides ongoing monitoring and transparent reporting.

What to expect in a monthly report:

• Crawl stats from Google Search Console (pages crawled, errors, index coverage).
• Core Web Vitals performance trends.
• Changes in organic traffic and keyword rankings, segmented by page or content cluster.
• Link profile changes (new links gained, lost links, toxic links flagged).

If your report only shows vanity metrics like “total sessions” without technical context, push for more detail. The real value of an agency is in the diagnosis, not just the dashboard.

Final Checklist: What to Demand from Your SEO Agency

• Did they run a full technical SEO audit within the first 30 days?
• Have they identified crawl budget issues and optimized your XML sitemap and `robots.txt`?
• Are Core Web Vitals part of their regular performance review?
• Do they have a clear canonicalization and duplicate content strategy?
• Is link building focused on editorial quality, not volume?
• Are they integrating accessibility best practices into on-page optimization?
• Do they provide transparent, actionable reports with technical metrics?

If the answer to any of these is “no,” it’s time to ask harder questions—or find a new partner. Technical SEO is the bedrock of everything else. Build it right, and the growth will follow.

---

For more on site navigation and image optimization, read our guides on site navigation SEO and image alt text best practices.