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Crawling, indexing, search intent and the pillars of SEO: what you need to understand to know how a website ranks in search engines and whether SEO suits you.

SEO (Search Engine Optimisation) is the set of techniques that help the pages of a website rank well in a search engine when someone looks for what you offer. When it works, those visits arrive without paying per click and don't depend on a daily budget.

This guide covers what's worth understanding before you start: how a search engine works, what crawling and indexing are, the pillars of SEO, how it differs from SEM and how to tell whether it's working. It's written for people who are starting out, whether you run a business or have been asked to make decisions about the website.

Contents:

When you search on Google, the results page mixes paid ads with organic results: websites, locations on a map, videos, images. SEO works on the organic ones. The aim is for your website or content to show up in a good position without paying for each visit.

The order is decided by the search engine's algorithm, a set of rules and signals that isn't public and changes over time. Google, Bing and Yandex each have their own. Working on SEO means understanding what they reward and making your website meet it. That's why it's also called organic ranking or web positioning.

A bit of history

The first directories and search engines, such as Yahoo! and AltaVista, appeared in the 1990s, and website owners realised that ranking higher brought in more customers. Google was founded in 1998 and quickly became the reference search engine.

Early algorithms were simple and could be manipulated with techniques like keyword stuffing, which means repeating a keyword to excess. Over time, search engines have refined their systems and moved from counting words to judging whether content is useful for the person searching. Those techniques no longer work and can do harm.

How a search engine works: crawling, indexing and rankings

Between publishing a page and seeing it in a search, there are three stages:

Crawling. A search engine robot discovers the URL (through a link, the sitemap, or because you've added the site to Google Search Console) and reads its code.
Indexing. The search engine analyses the content, interprets it (including anything generated with JavaScript) and decides whether to store it in its index.
Ranking. When someone searches, the search engine queries its index and orders the results by relevance and quality.

If a search engine can't find a URL, it can't crawl it. And if it doesn't crawl or index it, no amount of ranking work will help. That's why SEO starts before anyone talks about positions.

What can block crawling or indexing

robots.txt. Tells the robot which URLs not to crawl. Blocking crawling is not the same as removing a URL from the index.
Robots tag with noindex. Asks for the page not to be indexed. The robot has to be able to crawl the page to read it, so it isn't combined with a block in robots.txt.
Canonical tag. Points to the main URL when several are very similar. It's a hint, not an order.
Server and security. Security rules that block robots, or incorrect response codes (404, 5xx errors), can cut off crawling without anyone having decided it.
Search Console's URL removal tool. Hides a page temporarily. To remove it for good you need noindex, a 404 or a 410.

Crawled doesn't mean indexed

Google crawls more pages than it indexes. In Search Console you'll see this as “Crawled – currently not indexed” or “Discovered – currently not indexed”. The usual causes are thin or repeated content, near-identical pages and URLs that the site barely links to.

What about AI search?

AI assistants and AI summaries also need pages they can read, understand and consider trustworthy, so the fundamentals are the same. To see where SEO is heading, read our piece on current SEO trends. And if the goal is to appear in AI answers, we cover it with our AI SEO service.

What is search intent

Behind every search there is a need. Google tries to work it out and shows the type of page that best meets it. That's why a page that doesn't match the intent won't rank, however well optimised it is. Keywords are the terms users use to express that need.

They fall into four types:

Informational. The user wants to learn something. For example, “what is a sitemap”. Guides and articles fit.
Navigational. They're looking for a specific website or brand. For example, “La Teva Web contact”.
Commercial. They're comparing options before deciding. For example, “best SEO plugins for WordPress”. Comparisons and well-argued service pages fit.
Transactional. They want to act: hire, buy, request a quote. For example, “corporate website quote”. Service pages, categories and product pages fit.

A single keyword can mix intents. Before deciding which type of page to create, look at what Google shows for that search: the pages already ranking tell you what users expect. Within a main intent there are also smaller questions the page should answer along the way; these are micro-intents.

What SEO is for and why it matters

The goal of SEO is to improve a website's positions in search results so it receives more visits from people already looking for what you offer. It isn't interruption traffic, like an ad. It arrives with a specific need, which makes it especially valuable for winning customers.

That doesn't mean it's free. Visits carry no cost per click, but the work does cost something: strategy, content, technical work and monitoring. What makes it worthwhile is how it builds up:

A well-ranked page keeps receiving visits months after it's published, with no extra spend per visit.
The cost per customer tends to fall over time, unlike advertising, which stops when the budget runs out.
Many of the changes SEO calls for (more speed, better structure, clearer content) improve the website for everyone, not just the search engine.

How much SEO weighs depends on the business. An online-only shop lives on the traffic it wins on its website. A travel agency or a restaurant combines it with a physical location and word of mouth. In both cases, showing up when the customer is researching is an opportunity that a competitor will take if you don't.

SEO vs SEM

SEM is paid advertising on search engines, for example with Google Ads. Both channels appear on the same results page, but they work differently:

CriterionSEOSEM

Cost	Investment in work; no payment per click	Paid per click or per impression
Time to first results	Months	From day one
Duration	Results last as long as the website is maintained	Stop when spending stops
Control	Depends on the search engine and competition; a position can't be guaranteed	Control over budget, targeting and message
Best suited to	Sustained demand and medium-term growth	Launches, one-off campaigns and testing demand

They aren't mutually exclusive. SEM gives fast data on which searches convert, and that information helps prioritise SEO. In the long run, SEO reduces dependence on advertising. We handle the paid channel through our SEM agency service.

The pillars of SEO

SEO work falls into three areas that have to move together. If one fails, it limits the others: excellent content on a website the search engine can't crawl won't perform.

Technical SEO. Everything that depends on code and infrastructure: URL structure and internal linking, crawling and indexing, structured data, the mobile version and loading speed. It includes Core Web Vitals, the metrics that measure loading and interaction experience, such as INP.
Content. The text, images and video that answer what the user is looking for. This is where you decide which pages to create, with what intent and at what level of detail.
Authority and links. The links a website receives from other relevant sites, plus brand mentions and reputation. It's the signal that other sources trust you.

The first two count as on-site SEO, because they're carried out on your own website. The third counts as off-site, because it happens elsewhere.

Types of SEO

Local SEO. For businesses with customers nearby. It works on the Google Business Profile listing, reviews and consistent contact details, as well as the website.
International SEO. For websites serving several countries or languages. It needs a clear URL structure and the hreflang tag to tell the search engine which version to show each user.
Ecommerce SEO. Focused on categories and product pages, and on avoiding the duplication that filters create.
White hat and black hat. The first follows search engine guidelines. The second tries to manipulate them (bought links, hidden content, spam) and can end in a manual action or a sharp loss of visibility.

You can read more about these concepts in our SEO dictionary.

How an SEO project works

A well-planned project follows three steps:

Strategy. You analyse the context (sector and competitors), the demand (keyword research) and the state of the website (SEO audit). That determines what to prioritise.
Implementation. You carry out the technical, content and authority work the analysis has uncovered. Not everything is done at once: you start with what has the most impact.
Measurement and adjustment. You review what has changed in crawling, rankings and conversions, and correct course.

The starting point can be an existing website or one still in development. In the second case, the initial analysis shows whether the channel is worth pursuing before anything is designed.

The term “an SEO” also refers to the person who does this work: “an SEO audited the website and says it's poorly optimised”. If you'd rather delegate it, we do it through our SEO agency service.

How long SEO takes and how it's measured

As a guide, significant movement usually appears between three and six months in. It depends on the age of the domain, how competitive the sector is and the starting point. A new website in a highly competitive sector will take longer than an established one with specific technical problems.

The metrics worth following:

Impressions and clicks in Search Console, and which searches you appear for.
Positions of the keywords you've prioritised.
Indexed pages, to catch the ones the search engine is discarding.
Organic traffic, segmented by page type.
Conversions: forms, calls, bookings or sales that come from the organic channel.

Visits are a means, not the goal. A website with less traffic but more enquiries is doing better than one with more visits that doesn't convert. The indicators also evolve as the way people search changes; we cover this when measuring visibility in our SEO trends piece.

SEO tools

Tools are grouped by function:

Official search engine data: Google Search Console and Bing Webmaster Tools, both free and essential.
Web analytics: Google Analytics or an equivalent, to link traffic to conversions.
Keywords and competition: Ahrefs, Semrush or the Google Ads Keyword Planner.
Technical audits: Screaming Frog, which simulates a search engine crawl, and the audit tools in Ahrefs or Semrush.
Speed and experience: PageSpeed Insights, Lighthouse and the Core Web Vitals report in Search Console.
External links: Ahrefs, Semrush and the links report in Search Console.

Is SEO necessary?

It depends. Every project has a different market and demand. SEO is a good channel when people already search for what you sell, when customers research before deciding or when the catalogue is large. It adds little if there are no searches, for example with a product so new that nobody is looking for it yet, or if the business lives almost entirely on direct referrals.

A quick check: run the searches your customer would run and see what comes up. Then look up the search volume with a keyword tool. If there's demand and the current results can be improved, there's an opportunity. If there's no demand, you'll need to look for related topics or turn to other channels, such as advertising or social media.

Frequently asked questions

How long does SEO take to deliver results?

Between three and six months to see significant movement, depending on competition and the state of the website. Technical fixes show up sooner than rankings for new content.

How much does SEO cost?

It depends on the scope: the size of the website, how competitive the sector is and how many pages need work. There is usually an initial audit and strategy, followed by a monthly fee for the work. The quote is set after reviewing the website and the sector; you can request one here.

Can I do SEO myself?

The basics, yes: writing useful content, looking after titles and descriptions and following Search Console. The technical audit, keyword strategy and competing in contested sectors need more time and experience.

Does SEO work the same on every search engine?

The fundamentals are shared: crawling, indexing and useful content. Google handles most searches, so it's usually the priority, but Bing and other search engines follow similar principles.

Once a page ranks, is there nothing more to do?

There is. Competitors improve, algorithms change and users' searches evolve. A position is kept through regular reviews of content, technical work and links.

Keep reading

Current SEO trends: where search is heading and how to adapt.
AI SEO (GEO): how to build a brand's presence in AI answers.
INP and Core Web Vitals: the interaction metric Google measures.
SEO dictionary: every concept in one place.

If you already have a website and want to know where it stands, our SEO agency can review its crawling, indexing and content. Let's talk.

About the author

Bruno Díaz — Marketing Manager

Professional with a long career as a communication and digital marketing consultant, specializing in SEO, SEM and web projects. As Marketing Manager of the agency, I coordinate a great team of digital marketing technicians of which I am very proud.