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DIGITECH guide · 5 min read

What to Know When Looking for a Mobile SEO Agency

Most of your visitors arrive holding a phone, and Google indexes the mobile version of your pages. A mobile SEO agency makes sure that version is the complete, fast one. This guide explains what the work involves and how to judge the people offering it.

Written by

Priya Natarajan

Technical SEO Lead

Engineer turned SEO · Site architecture, Core Web Vitals and structured data for multi-location groups

Editorially reviewed by

Elias Morgan

Editorial Director

Former healthcare trade editor · Checks every guide against its cited sources before publication

Published · Updated · Reviewed February 25, 2025

In brief

  1. Google uses the mobile version of a page for indexing and ranking. What the smartphone crawler sees is what gets indexed.
  2. Responsive design on a single URL is Google’s recommended configuration. It removes an entire class of duplication problems.
  3. Speed is measured, not felt. Core Web Vitals have published thresholds you can hold an agency to.
  4. Content parity matters as much as speed. Text, links, images and structured data missing from the mobile HTML are effectively missing.
  5. No agency can guarantee rankings or a speed figure before an audit. Ask for a plan and a measurement method instead.

Part 01

What a mobile SEO agency actually does

The job is to make the mobile experience of your site the primary one, in the eyes of visitors and crawlers alike. In practice that means auditing what Googlebot’s smartphone crawler sees, fixing layout and performance problems, and confirming that nothing important is missing on small screens.

Definition

Mobile-first indexing

Google’s practice of using the smartphone version of a page’s content for indexing and ranking. Google announced in late 2023 that the switch was complete for all sites, so there is no separate desktop index to fall back on.

A credible agency separates three workstreams: layout (how pages adapt to the screen), performance (how fast pages load and respond), and parity (whether mobile pages carry the same content, links, metadata and structured data as desktop). Each has its own tests and its own fixes, and a proposal that blurs them is usually selling a theme change.

Part 02

Responsive design and the one-URL rule

There are three ways to serve a site to phones. Google supports all three but recommends responsive design, where one URL serves the same HTML and the stylesheet adapts the layout.

Three mobile configurationsSchematic
Recommended by Google

Responsive design

One URL, one HTML document. CSS adapts the layout to the screen. Simplest to crawl, share and measure.

Supported

Dynamic serving

One URL, but the server sends different HTML by user agent. Needs the Vary header and testing on both.

Supported, legacy

Separate URLs

A second site such as m.example.com, tied together with alternate and canonical tags. Easy to get wrong.

Responsive design keeps one URL and one set of HTML for every device. Dynamic serving and separate URLs are supported, but each adds a layer that has to be configured and tested correctly, and each is a common source of indexing mistakes.

If an agency proposes a separate mobile site today, ask why. For nearly every business the right answer is a responsive build that carries the same content at every screen size. The exceptions are rare and should come with a specific technical reason.

Caution

Hidden is not the same as missing

Accordions and tabs are fine; Google indexes content inside them. Content that is removed from the mobile HTML entirely is a different matter: it is not indexed. Ask the agency to show you the mobile source, not just the screen.

Part 03

Mobile speed and content parity

Speed is where mobile SEO claims get loudest and least precise. Hold them to published numbers. Google’s Core Web Vitals define three metrics, each with a “good” threshold measured at the 75th percentile of real visits to a page.

Core Web Vitals thresholdsSchematic, not to scale
LCPLargest Contentful Paint
Good
2.5 s or less
Needs work
2.5 s to 4 s
Poor
over 4 s
INPInteraction to Next Paint
Good
200 ms or less
Needs work
200 to 500 ms
Poor
over 500 ms
CLSCumulative Layout Shift
Good
0.1 or less
Needs work
0.1 to 0.25
Poor
over 0.25
Good thresholds as published by Google. Field data from real visitors decides whether a page passes, not a single lab run on a fast laptop.

The three metrics and their usual mobile culprits

MetricMeasuresGoodTypical mobile culprit
LCPTime until the largest visible element has loaded2.5 seconds or lessOversized hero images, slow server response
INPResponsiveness to taps and keypresses across the visit200 milliseconds or lessHeavy scripts blocking the main thread
CLSVisual stability while the page loads0.1 or lessImages without dimensions, late-loading embeds

Parity is the quieter half. Compare the mobile and desktop HTML for headings, body text, internal links, image alt text, structured data and meta tags. A page that is fast but missing half of its links on mobile has traded one problem for another.

Part 04

How to choose a mobile SEO agency

The questions below are not trick questions. A capable agency will have ready answers and will be pleased you asked. Tick them off during the first conversation.

Questions worth asking

0 of 5 ticked

Claims to question

  • A guaranteed PageSpeed score
  • Guaranteed page-one rankings on mobile
  • Mobile is handled automatically by the theme
  • One framework or plugin will fix it

What to ask for instead

  • A Core Web Vitals plan with field-data targets and stated assumptions
  • A ranked list of indexing, speed and parity issues with owners and dates
  • An audit of the theme’s actual mobile output, including the scripts it loads
  • Reasoning about your templates and third-party scripts, not a product name

Part 05

Measuring the work

Set the baseline before any change is made: Core Web Vitals field data per template, mobile indexing coverage in Search Console, and the conversion rate of mobile sessions. Then change one thing at a time where you can, and measure again on the same basis.

A measurement loopProcess diagram
Repeat on a fixed cadence
01BaselineSame measures, same percentile
02ChangeOne thing at a time
03MeasureField data, 28-day window
04ReportIncluding what did not move
Baseline, change, measure, report. The cadence matters less than keeping the same measures and the same percentile throughout, so that months can be compared honestly.

Expect honest reporting to include things that did not move. Field data is aggregated over a trailing 28-day window, rankings fluctuate, and seasonality affects mobile traffic more than desktop. An agency that reports a flat month plainly is more trustworthy than one that never has one.

Mobile is one lens on the same foundations described in the overview guide, Understanding the Different Types of SEO. If the audit turns up crawl or indexing problems that are not specific to mobile, that is where technical SEO takes over.

Questions readers ask

Is mobile SEO different from regular SEO?

It is a lens on the same work. The foundations, crawlability, content and authority, are identical. Mobile SEO makes sure the smartphone version of the site carries them, because that version is what Google indexes.

Do we need a separate mobile website?

Almost never. Responsive design on one URL is Google's recommended approach, and it avoids the duplication and canonical problems that separate mobile URLs create.

What counts as good mobile page speed?

Google publishes Core Web Vitals thresholds: LCP of 2.5 seconds or less, INP of 200 milliseconds or less, and CLS of 0.1 or less, measured at the 75th percentile of real visits. Those are the numbers to aim for. A single lab score is not the same thing.

Can an agency guarantee rankings or a speed score?

No. Google states that no one can guarantee rankings, and real-world speed depends on devices and networks the agency does not control. Ask for a plan with targets and the assumptions behind them instead.

How does this guide relate to the other SEO guides?

This guide sits under the overview, [Understanding the Different Types of SEO](/seo/), which explains how mobile fits alongside technical, local and the other specialisations.

Sources

  1. Mobile-first indexing best practices — Google Search Central
  2. Get started with mobile-friendliness — Google Search Central
  3. Mobile-first indexing has landed — Google Search Central Blog, October 2023
  4. Understanding Core Web Vitals and Google search results — Google Search Central
  5. Web Vitals — web.dev
  6. Understanding page experience in Google Search results — Google Search Central
  7. Do you need an SEO? — Google Search Central
  8. Understanding the Different Types of SEO — DIGITECH, overview guide
  9. Technical SEO Agency — DIGITECH, published site

About this guide

Written by

Priya Natarajan

Technical SEO Lead

Engineer turned SEO · Site architecture, Core Web Vitals and structured data for multi-location groups

Read full bio

Priya leads technical SEO and works alongside the web design team. She came to search from software engineering and handles site architecture, performance and structured data for multi-location healthcare groups and law firms. She writes the checklists the team actually uses.

View profile & articles →

Editorially reviewed by

Elias Morgan

Editorial Director

Former healthcare trade editor · Checks every guide against its cited sources before publication

Read full bio

Elias runs editorial review for everything DIGITECH publishes. He reads each draft against the sources it cites, checks the claims a client could be held to, and signs off on the review date that appears on the page. Before DIGITECH he edited a healthcare trade publication for eight years.

View profile & articles →

Published · Updated