diff --git a/src/__tests__/cli.test.ts b/src/__tests__/cli.test.ts
index 0d0e520..1ab5cd1 100644
--- a/src/__tests__/cli.test.ts
+++ b/src/__tests__/cli.test.ts
@@ -62,6 +62,11 @@ describe('parseArgs', () => {
   it('throws when --fail-on is given without a value', () => {
     expect(() => parseArgs(['old.json', 'new.json', '--fail-on'])).toThrow(/Invalid --fail-on/);
   });
+
+  it('parses --runtime-only as true (default false)', () => {
+    expect(parseArgs(['old.json', 'new.json']).runtimeOnly).toBe(false);
+    expect(parseArgs(['old.json', 'new.json', '--runtime-only']).runtimeOnly).toBe(true);
+  });
 });
 
 describe('gateFailures', () => {
diff --git a/src/__tests__/parser.test.ts b/src/__tests__/parser.test.ts
index 1ccfe0f..a2c8b8d 100644
--- a/src/__tests__/parser.test.ts
+++ b/src/__tests__/parser.test.ts
@@ -75,6 +75,23 @@ describe('parse (CycloneDX)', () => {
     expect(sbom.components[1].hashes).toBeUndefined();
   });
 
+  it('extracts the component scope (dev/test vs runtime) (issue #56)', () => {
+    const sbom = parse({
+      bomFormat: 'CycloneDX',
+      specVersion: '1.4',
+      components: [
+        { name: 'runtime-pkg', version: '1.0.0', scope: 'required' },
+        { name: 'dev-pkg', version: '1.0.0', scope: 'optional' },
+        { name: 'excluded-pkg', version: '1.0.0', scope: 'excluded' },
+        { name: 'no-scope-pkg', version: '1.0.0' },
+      ],
+    });
+    expect(sbom.components[0].scope).toBe('required');
+    expect(sbom.components[1].scope).toBe('optional');
+    expect(sbom.components[2].scope).toBe('excluded');
+    expect(sbom.components[3].scope).toBeUndefined();
+  });
+
   it('parses vulnerabilities', () => {
     const sbom = parse(cyclonedxFixture);
     expect(sbom.vulnerabilities).toHaveLength(1);
diff --git a/src/cli.ts b/src/cli.ts
index d49b17b..fdc30c7 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -49,18 +49,26 @@ Arguments:
 
 Options:
   --format <fmt>   Output format: text (default), json, or markdown
+  --fail-on <sev>  Fail (exit 3) when a new CVE at/above this severity appears:
+                   none (default), low, medium, high, critical, any
+  --runtime-only   Only consider runtime components (scope=required); dev/test
+                   (scope=optional/excluded) dependencies are filtered out of
+                   the diff and the --fail-on gate
   -h, --help       Show this help and exit
   -v, --version    Print the installed version and exit
 
 Examples:
   sbom-diff old.json new.json
   sbom-diff old.json new.json --format json
-  sbom-diff old.json new.json --format markdown`;
+  sbom-diff old.json new.json --format markdown
+  sbom-diff old.json new.json --runtime-only --fail-on high`;
 
 export interface ParsedArgs {
   positional: string[];
   format: ReportFormat;
   failOn: FailOn;
+  /** true when --runtime-only was requested (filter dev/test deps) */
+  runtimeOnly: boolean;
   /** true when -h/--help was requested */
   help: boolean;
   /** true when -v/--version was requested */
@@ -72,8 +80,8 @@ export interface ParsedArgs {
  * the CI/CD gate policy.
  *
  * Supports `--format text`, `--format=text`, `--fail-on high`, `--fail-on=high`,
- * and flags appearing in any position relative to the positional file paths.
- * Defaults to `text` format and a `none` gate policy.
+ * `--runtime-only`, and flags appearing in any position relative to the
+ * positional file paths. Defaults to `text` format and a `none` gate policy.
  *
  * `-h`/`--help` and `-v`/`--version` short-circuit parsing so they always
  * work — even alongside otherwise-invalid arguments — and never throw.
@@ -82,15 +90,16 @@ export interface ParsedArgs {
  */
 export function parseArgs(argv: string[]): ParsedArgs {
   if (argv.some(a => a === '-h' || a === '--help')) {
-    return { positional: [], format: 'text', failOn: 'none', help: true, version: false };
+    return { positional: [], format: 'text', failOn: 'none', runtimeOnly: false, help: true, version: false };
   }
   if (argv.some(a => a === '-v' || a === '-V' || a === '--version')) {
-    return { positional: [], format: 'text', failOn: 'none', help: false, version: true };
+    return { positional: [], format: 'text', failOn: 'none', runtimeOnly: false, help: false, version: true };
   }
 
   const positional: string[] = [];
   let format: ReportFormat = 'text';
   let failOn: FailOn = 'none';
+  let runtimeOnly = false;
 
   for (let i = 0; i < argv.length; i++) {
     const arg = argv[i];
@@ -102,6 +111,8 @@ export function parseArgs(argv: string[]): ParsedArgs {
       failOn = assertFailOn(argv[++i]);
     } else if (arg.startsWith('--fail-on=')) {
       failOn = assertFailOn(arg.slice('--fail-on='.length));
+    } else if (arg === '--runtime-only') {
+      runtimeOnly = true;
     } else if (arg.startsWith('-')) {
       throw new Error(`Unknown option: ${arg}\n${USAGE}`);
     } else {
@@ -109,7 +120,7 @@ export function parseArgs(argv: string[]): ParsedArgs {
     }
   }
 
-  return { positional, format, failOn, help: false, version: false };
+  return { positional, format, failOn, runtimeOnly, help: false, version: false };
 }
 
 /**
@@ -237,7 +248,7 @@ export async function loadSbom(path: string, label: string): Promise<SBOM> {
 }
 
 async function main(): Promise<void> {
-  const { positional, format, failOn, help, version } = parseArgs(process.argv.slice(2));
+  const { positional, format, failOn, runtimeOnly, help, version } = parseArgs(process.argv.slice(2));
 
   if (help) {
     console.log(HELP);
@@ -261,11 +272,17 @@ async function main(): Promise<void> {
     loadSbom(newPath, 'new'),
   ]);
 
-  const report = diff(oldSBOM, newSBOM);
+  // With --runtime-only, drop dev/test (scope=optional/excluded) components so
+  // the diff and the --fail-on gate consider only production dependencies.
+  // A component without a scope is runtime by CycloneDX's default, so it stays.
+  const aFinal = runtimeOnly ? filterRuntimeOnly(oldSBOM) : oldSBOM;
+  const bFinal = runtimeOnly ? filterRuntimeOnly(newSBOM) : newSBOM;
+
+  const report = diff(aFinal, bFinal);
 
   console.log(renderReport(report, format));
 
-  const warning = gateWarning(oldSBOM, newSBOM, failOn);
+  const warning = gateWarning(aFinal, bFinal, failOn);
   if (warning) console.error(warning);
 
   const failures = gateFailures(report, failOn);
@@ -278,6 +295,19 @@ async function main(): Promise<void> {
   }
 }
 
+/**
+ * Return a copy of the SBOM with only runtime components (those whose scope is
+ * "required" or unset). Dev/test/build dependencies (scope "optional" or
+ * "excluded") are filtered out. Vulnerabilities are kept as-is — they reference
+ * components by ref, and filtering them would misattribute blast radius.
+ */
+function filterRuntimeOnly(sbom: SBOM): SBOM {
+  return {
+    ...sbom,
+    components: sbom.components.filter(c => c.scope === undefined || c.scope === 'required'),
+  };
+}
+
 // Only run when invoked directly (not when imported by tests).
 const invokedPath = process.argv[1];
 if (invokedPath && import.meta.url === pathToFileURL(invokedPath).href) {
diff --git a/src/parser.ts b/src/parser.ts
index 0b5accd..8c77996 100644
--- a/src/parser.ts
+++ b/src/parser.ts
@@ -39,6 +39,7 @@ export function parseCycloneDX(obj: Record<string, unknown>): SBOM {
     license: extractCycloneDXLicense(c),
     ecosystem: extractEcosystemFromPurl(typeof c.purl === 'string' ? c.purl : ''),
     supplier: extractCycloneDXSupplier(c),
+    scope: extractCycloneDXScope(c),
     hashes: extractCycloneDXHashes(c),
   }));
 
@@ -239,9 +240,21 @@ function extractSPDXLicense(pkg: Record<string, unknown>): string | undefined {
 }
 
 function extractCycloneDXSupplier(c: Record<string, unknown>): string | undefined {
-  const supplier = c.supplier as Record<string, unknown> | undefined;
-  if (!supplier) return undefined;
-  return typeof supplier.name === 'string' ? supplier.name : undefined;
+  const supplier = c.supplier;
+  if (typeof supplier !== 'object' || supplier === null) return undefined;
+  return typeof (supplier as Record<string, unknown>).name === 'string' ? (supplier as Record<string, unknown>).name as string : undefined;
+}
+
+/**
+ * Extract the CycloneDX component scope ("required" / "optional" / "excluded").
+ * Returns undefined when absent, which is the meaning of "no scope" in CDX:
+ * scope defaults to "required" when omitted, but we keep it undefined so the
+ * reporter can show "default" rather than a misleading explicit value.
+ */
+function extractCycloneDXScope(c: Record<string, unknown>): 'required' | 'optional' | 'excluded' | undefined {
+  const scope = c.scope;
+  if (scope === 'required' || scope === 'optional' || scope === 'excluded') return scope;
+  return undefined;
 }
 
 function extractCycloneDXAffects(v: Record<string, unknown>): string[] {
diff --git a/src/types.ts b/src/types.ts
index 51b634f..9efec6f 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -21,6 +21,12 @@ export interface Component {
   ecosystem?: string;
   /** Supplier / organization */
   supplier?: string;
+  /**
+   * CycloneDX component scope: "required" (runtime), "optional"
+   * (dev/test/build), or "excluded". Lets gates/reports distinguish
+   * production dependencies from dev/test ones (issue #56).
+   */
+  scope?: 'required' | 'optional' | 'excluded';
   /** Hash values keyed by algorithm (sha256, sha1, md5) */
   hashes?: Record<string, string>;
 }