How to Choose a Web Development Agency: 1,140 Case Studies

Most guides to choosing a web development agency tell you to check its tech stack, its process and its portfolio. Those show what an agency can build. They don't show what its builds did for the business, and most web development case studies don't either.

This guide shows what to check instead. Each step below comes from 1,140 web development case studies published by 128 agencies and indexed in OpenServed's directory. We counted what agencies report, what they leave out, and what a typical published result looks like, so every piece of advice here comes with evidence.

Data as of November 2026. The full numbers are in Web Development Statistics 2026.

The short answer

1. Know what a realistic result looks like. The median published case study reports a 60% increase in website traffic and a 99% increase in conversions or leads.
2. Decide what kind of build you need. A quarter of web development case studies are ecommerce builds, and they report sales. Other builds rarely report a result.
3. Ask what the build achieved, not only what was built. 36% of web development case studies contain no number at all, and 30% report a business result.
4. If you're migrating, ask what happens to your traffic. 8% of case studies are migrations or rebuilds, and only 10% of those report traffic.
5. Ask for speed and performance before and after, with dates. 7% report page speed, and none say how long the project took.
6. Decide who handles design and SEO. 61% of web development case studies also list web design, and those sold with SEO include a measured result 79% of the time, against 37% without.
7. Check that web development is a core service. 84 of the 128 agencies have five or fewer web development case studies.
8. Ask whether the client confirmed it. Only 4.6% of web development case studies are Client-verified.

1. Know what a realistic result looks like

The median web development case study reports a 60% increase in website traffic. Among the 226 case studies that state a traffic gain, half fall between 26% and 129%. About two in three report a gain under 100%. A rebuild usually starts from a site that already has visitors, so percentage gains are modest.

Business results grow more than traffic. The median reported increase is 99% for conversions or leads (90 case studies), 71% for revenue (115) and 43% for conversion rate (42).

Speed is where development shows most. The median reported cut in page load time is 49% (35 case studies, middle half 37% to 70%). The median drop in bounce rate is 14% (29).

These are the wins. Agencies publish the projects that went well, so a typical project is likely to land lower. One agency, Coalition Technologies, supplies 47 of the 226 traffic data points. Without it, the median traffic gain is 56%.

Four-digit percentages are rare. Only 16 case studies (1.4%) contain a claim of 1,000% or more.

What to do: ask an agency what result it expects from your build and what that estimate is based on. A range near these figures, tied to clients like you, is a good sign. Be wary of a guarantee, or of a traffic promise far above a doubling with no explanation.

2. Decide what kind of build you need

A quarter of web development case studies are ecommerce builds. 290 of the 1,140 (25%) are for online stores, on platforms such as Magento or Adobe Commerce, Shopify and WooCommerce, or for retail clients. They are measured differently from other builds.

Store builds report sales; other builds rarely report a result. 36% of ecommerce builds report revenue or sales and 10% report conversion rate, against 8% and 3% of other builds. 43% of ecommerce builds report a business result of any kind, against 26% of other builds.

Store builds report modest gains. The median reported revenue gain for ecommerce builds is 60% (73 case studies) and the median conversion rate gain 40% (24).

Other builds are measured in leads, when they are measured at all. For builds that aren't ecommerce, the median reported gain in conversions or leads is 126% (75 case studies). 38% of them contain no number at all.

Few case studies name the platform. 13% name a content management or ecommerce platform in their results. WordPress is named most often, in 61 case studies, followed by Magento or Adobe Commerce (46), Shopify (16) and WooCommerce (14).

What to do: before you talk to agencies, decide what the build has to achieve: sales and conversion rate for a store, leads for a service business, or something else for a portal or internal tool. Then shortlist agencies whose case studies show that result, on the platform you need.

3. Ask what the build achieved, not only what was built

36% of web development case studies contain no number at all. 410 of the 1,140 list only what was built, such as a new platform, an integration or a site launch. They show the work, not the result.

Only about one in ten shows traffic and what it turned into. 11% of case studies report traffic alongside revenue, leads, conversions or conversion rate. 16% report traffic with no business result, 20% a business result with no traffic, and 54% neither.

Larger clients are less likely to show a business result. A business result appears in 43% of small-business case studies and 44% of medium ones, but 34% of large and 33% of enterprise ones. Client size is recorded for 33% of these case studies.

Some industries rarely measure their builds. A business result appears in 39% of retail and ecommerce case studies and 34% of manufacturing ones, but 21% of education and nonprofit and 19% of software ones.

What to do: ask what each build in the portfolio achieved after launch, in sales, leads or conversion rate. If the agency's case studies list features and integrations with no results, ask what changed for the client's business.

4. If you're migrating, ask what happens to your traffic

Migrations are common, and they rarely report traffic. 96 web development case studies (8%) mention a migration, replatform or rebuild. Only 10 of them (10%) report what happened to traffic, though a migration is when a site is most likely to lose it.

Migrations rarely report any result. 19% of migration case studies report a business result and 8% report page speed.

What to do: if you're moving platforms or changing URLs, ask for a written plan for redirects, search traffic and analytics before work starts. Ask to see traffic before and after a past migration, and agree how soon after launch traffic will be checked.

5. Ask for speed and performance before and after, with dates

Web development case studies measure speed more than web design ones, but still rarely. 7% report a page speed result, against 3% of web design case studies. Accessibility appears in 2%, mobile in 6%, and uptime or security in 2%.

Speed results rarely come with a business result. Only 20% of the case studies that report a speed gain also report revenue, leads, conversions or conversion rate.

The starting point and the timing are usually missing. Only 5.4% give a before and an after number, 8% mention any time period and 2.2% say how long after launch the result was measured.

None say how long the project took, and none state the budget.

What to do: ask for page speed, Core Web Vitals and accessibility scores before and after launch, measured the same way, with dates. Get the expected timeline, the fee and what support is included after launch in writing, since our data has none of these.

6. Decide who handles design and SEO

Most web development comes with design. 701 of the 1,140 case studies (61%) also list web design. Those projects report a business result less often (25% against 38% for development without design) and are more likely to contain no number at all (41% against 28%). For how the two compare, see Web Design vs Web Development.

SEO decides whether a result is reported at all. 356 web development case studies (31%) also list SEO. 79% of those include a measured result, against 37% of those without SEO. Traffic appears in 54% against 14%, and a business result in 39% against 26%.

Reported gains are much higher with SEO. The median traffic gain is 76% with SEO (161 case studies) against 36% without (65). For conversions or leads it is 156% against 51%, and for revenue 107% against 41%.

Enterprises rarely buy SEO with development. SEO is listed in 70% of small-business web development case studies, 49% of medium, 40% of large and 8% of enterprise ones.

What to do: ask who designs the site and who protects its search traffic, whether they are in-house or partners, and how the work is split. If the agency only builds, make sure someone owns design and SEO before launch.

7. Check that web development is a core service

Many agencies list web development and have only a few case studies for it. 128 of the 330 agencies in our directory have published a web development case study. 84 of the 128 have five or fewer, and only 17 have 20 or more.

Web development is the main service for a minority. Of the 98 agencies that have ten or more case studies in total and list web development, 23 have it in at least half of them.

A few agencies publish much of the proof. Coalition Technologies, Wakefly and GCC Marketing account for 19% of the web development case studies.

What to do: count how many web development case studies an agency has, and how many are on the platform and for the kind of business you need. If it has a handful, ask who writes the code, whether developers are in-house, and to see builds launched in the last year.

8. Ask whether the client confirmed it

Only 4.6% of web development case studies are Client-verified. That is 53 of 1,140, from 38 agencies, about half the share for web design. On OpenServed, Client-verified means the client has confirmed the results. Everything else is as reported by the agency.

There are too few verified results to compare. No metric has more than 8 verified data points. Verified case studies are less likely to contain no number, 26% against 36% of agency-reported ones.

What to do: ask whether you can speak with the client behind a case study, and visit the live site. A reference call is a reasonable thing to ask for before you sign.

Questions to ask a web development agency

Each question below comes from one of the eight steps. A good answer is specific; a warning sign is a number with nothing behind it.

1. What result should we expect, and what is that based on? A good answer is a range tied to clients like you, near typical published gains. A warning sign is a guarantee, or traffic promised far above a doubling.
2. What kind of build is this, and what will it be measured on? A good answer is sales and conversion rate for a store, or leads for a lead site. A warning sign is no agreed measure before the build starts.
3. What did your past builds achieve? A good answer shows sales, leads or conversion rate after launch, with the client named. A warning sign is a list of features and integrations with no result.
4. If we're migrating, how will you protect our traffic? A good answer is a redirect plan and traffic shown before and after past migrations. A warning sign is no plan for redirects, or migrations with no traffic numbers.
5. How fast will the site be, and how will you prove it? A good answer gives speed scores before and after launch, with dates. A warning sign is "faster" with no number and no date.
6. Who handles design and SEO? A good answer names a team or partner for each, with a plan for search. A warning sign is development alone, with no answer on search traffic.
7. How much of your work is web development? A good answer is many development case studies, on the platform you need. A warning sign is a handful of builds among other services.
8. Can we speak with the client, or is the result verified? A good answer is a reference call or a client-verified case study. A warning sign is no named client and no reference.

Red flags when hiring a web development agency

• A portfolio with no results. 36% of web development case studies contain no number at all. A feature list is not proof that the build worked.
• A guaranteed result. Published traffic gains have a median of 60%. Nobody can promise where your site will land.
• A migration with no traffic plan. Only 10% of migration case studies report traffic. Ask what happened to it, and how the agency will protect yours.
• "Faster" with no number. Only 7% of case studies report page speed, and only 5.4% give a before and an after number.
• No one responsible for search. Web development without SEO includes a measured result only 37% of the time.
• Web development as a side service. 84 of the 128 agencies have five or fewer web development case studies.
• No reference. Only 4.6% of web development case studies are Client-verified.

One more thing to settle before you sign: get the fee, the timeline, the support after launch and who owns the code, hosting and accounts in writing. Our data has no pricing or project lengths, so we can't tell you what is fair, but you should know exactly what you are paying for.

Related guides

• How to choose a digital marketing agency, the general guide across every service.
• How to choose an SEO agency, if search traffic is part of the goal.
• How to choose a web design agency, if the look and feel of the site come first.

Find a web development agency

OpenServed's web development agency directory lists agencies by the case studies they have published, so you can check each of the steps above before you make contact. You can narrow it to your industry, such as ecommerce, manufacturing or healthcare, or to your size, such as small business or enterprise. Look for the Client-verified badge on results the client has confirmed.

About the data

The figures in this guide come from the 1,140 case studies in OpenServed's directory that list Web Development as a service, published by 128 agencies, as of November 2026. Results are as reported by each agency; only 53 have been confirmed by the client. Agencies publish their best work, so these numbers describe successful projects, not average ones. Medians use stats that state a percentage change, one per case study. Stats that name paid media, ads, email or social media are not counted as web development results; organic and SEO stats are kept, because a new site affects search traffic. A business result means revenue, leads, conversions or conversion rate. Load time and bounce rate are reported as reductions. Ecommerce builds are case studies for retail and ecommerce clients, or whose results mention an online store, a commerce platform, orders, transactions or checkout.