diff --git a/tools/cli/internal/openapi/oasdiff.go b/tools/cli/internal/openapi/oasdiff.go
new file mode 100644
index 000000000..be42623f7
--- /dev/null
+++ b/tools/cli/internal/openapi/oasdiff.go
@@ -0,0 +1,74 @@
+package openapi
+
+import (
+	"fmt"
+	"mongodb/openapi/tools/cli/internal/openapi/errors"
+	"os"
+
+	"github.com/tufin/oasdiff/diff"
+	"github.com/tufin/oasdiff/load"
+)
+
+type OasDiff struct {
+	base     *load.SpecInfo
+	external *load.SpecInfo
+	config   *diff.Config
+	specDiff *diff.Diff
+	parser   Parser
+}
+
+func NewOasDiff(base *load.SpecInfo) *OasDiff {
+	return &OasDiff{
+		base:   base,
+		parser: NewOpenAPI3(),
+	}
+}
+
+func (o *OasDiff) MergeOpenAPISpecs(paths []string) (*load.SpecInfo, error) {
+	for _, p := range paths {
+		spec, err := o.parser.CreateOpenAPISpecFromPath(p)
+		if err != nil {
+			return nil, err
+		}
+
+		o.config = &diff.Config{
+			IncludePathParams: true,
+		}
+
+		specDiff, err := diff.Get(o.config, o.base.Spec, spec.Spec)
+		if err != nil {
+			_, _ = fmt.Fprintf(os.Stderr, "error in calculating the diff of the specs: %s", err)
+			return nil, err
+		}
+
+		o.specDiff = specDiff
+		o.external = spec
+		err = o.mergeSpecIntoBase()
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return o.base, nil
+}
+
+func (o OasDiff) mergeSpecIntoBase() error {
+	return o.mergePaths()
+}
+
+func (o OasDiff) mergePaths() error {
+	pathsToMerge := o.external.Spec.Paths
+	basePaths := o.base.Spec.Paths
+	for k, v := range pathsToMerge {
+		if _, ok := basePaths[k]; !ok {
+			basePaths[k] = v
+		} else {
+			return errors.PathConflictError{
+				Entry: k,
+			}
+		}
+	}
+
+	o.base.Spec.Paths = basePaths
+	return nil
+}
diff --git a/tools/cli/internal/openapi/openapi3.go b/tools/cli/internal/openapi/openapi3.go
new file mode 100644
index 000000000..840dbfc5c
--- /dev/null
+++ b/tools/cli/internal/openapi/openapi3.go
@@ -0,0 +1,31 @@
+package openapi
+
+import (
+	"github.com/getkin/kin-openapi/openapi3"
+	"github.com/tufin/oasdiff/load"
+)
+
+type OpenAPI3 struct {
+	IsExternalRefsAllowed    bool
+	CircularReferenceCounter int
+}
+
+func NewOpenAPI3() *OpenAPI3 {
+	return &OpenAPI3{
+		IsExternalRefsAllowed:    true,
+		CircularReferenceCounter: 10,
+	}
+}
+
+func (o *OpenAPI3) CreateOpenAPISpecFromPath(path string) (*load.SpecInfo, error) {
+	loader := openapi3.NewLoader()
+	loader.IsExternalRefsAllowed = true
+	openapi3.CircularReferenceCounter = 10
+
+	spec, err := load.LoadSpecInfo(loader, load.NewSource(path))
+	if err != nil {
+		return nil, err
+	}
+
+	return spec, nil
+}