diff --git a/README.md b/README.md
index 072abd3..6cdbe9c 100644
--- a/README.md
+++ b/README.md
@@ -47,7 +47,7 @@ jobs:
 | `duplicate-threshold`  | Threshold for warning about packages with multiple versions                    | No       | `1`                                       |
 | `base-packages`        | Glob pattern for base branch pack files (e.g., `"./base-packs/*.tgz"`)         | No       | None                                      |
 | `source-packages`      | Glob pattern for source branch pack files (e.g., `"./source-packs/*.tgz"`)     | No       | None                                      |
-| `pack-size-threshold`  | Threshold (in bytes) for warning about significant increase in total pack size | No       | `50000`                                   |
+| `pack-size-threshold`  | Threshold (in bytes) for warning about significant increase in total pack size. Set to `-1` to always report size changes. | No       | `50000`                                   |
 | `detect-replacements`  | Detect modules which have community suggested alternatives                     | No       | `true`                                    |
 | `working-directory`    | Working directory to scan for package lock file                                | No       | None                                      |
 
@@ -90,11 +90,26 @@ The action accepts glob patterns to locate package tarballs for comparison:
 
 - **`base-packages`** - Glob pattern for base branch pack files (e.g., `"./base-packs/*.tgz"`)
 - **`source-packages`** - Glob pattern for source branch pack files (e.g., `"./source-packs/*.tgz"`)
-- **`pack-size-threshold`** - Threshold in bytes for warning about significant pack size increases
+- **`pack-size-threshold`** - Threshold in bytes for warning about significant pack size increases. Set to `-1` to always report bundle size changes.
 
 > [!NOTE]
 > Package bundle analysis only runs when both `base-packages` and `source-packages` are provided. If these inputs are not set, this feature is skipped entirely.
 
+When the bundle size does not change between base and source, no message is posted. Set `pack-size-threshold` to `-1` to always report, including a confirmation when there is no change.
+
+### Always Report Bundle Size Changes
+
+To always report bundle size changes, set `pack-size-threshold` to `-1`. All changed packages are shown in a single table. When only decreases occur, the report is marked with 🎉:
+
+```yaml
+- name: Create Diff
+  uses: e18e/action-dependency-diff@v1
+  with:
+    base-packages: './base-packs/*.tgz'
+    source-packages: './source-packs/*.tgz'
+    pack-size-threshold: -1
+```
+
 You can see an example of how to set this up in the [bundle difference workflow](./recipes/bundle-diff.yml).
 
 ## Module Replacements
diff --git a/action.yml b/action.yml
index 9c4c9b4..658e4a9 100644
--- a/action.yml
+++ b/action.yml
@@ -33,7 +33,7 @@ inputs:
     description: 'Glob pattern for source branch pack files (e.g., "./source-packs/*.tgz")'
     required: false
   pack-size-threshold:
-    description: 'Threshold (in bytes) for warning about significant increase in total pack size'
+    description: 'Threshold (in bytes) for warning about significant increase in total pack size. Set to -1 to always report size changes.'
     required: false
     default: '50000'
   duplicate-threshold:
diff --git a/src/checks/bundle-size.ts b/src/checks/bundle-size.ts
index 8400e4e..476c3c5 100644
--- a/src/checks/bundle-size.ts
+++ b/src/checks/bundle-size.ts
@@ -1,6 +1,10 @@
 import {formatBytes} from '../common.js';
 import {comparePackSizes, type PackInfo} from '../packs.js';
 
+function formatBytesSigned(bytes: number): string {
+  return `${bytes > 0 ? '+' : ''}${formatBytes(bytes)}`;
+}
+
 export async function scanForBundleSize(
   messages: string[],
   basePacks: PackInfo[],
@@ -11,8 +15,63 @@ export async function scanForBundleSize(
     return;
   }
   const comparison = comparePackSizes(basePacks, sourcePacks, threshold);
+
+  if (threshold === -1) {
+    const changedPacks = comparison.packChanges.filter(
+      (change) => change.exceedsThreshold
+    );
+
+    if (changedPacks.length === 0) {
+      messages.push(`## 📦 Package Bundle Size\n\nNo bundle size changes.`);
+      return;
+    }
+
+    if (changedPacks.length > 0) {
+      const hasDecreases = changedPacks.some((c) => c.sizeChange < 0);
+      const hasIncreases = changedPacks.some((c) => c.sizeChange > 0);
+
+      const heading =
+        hasDecreases && hasIncreases
+          ? '## 📦 Package Bundle Size Changes'
+          : hasDecreases
+            ? '## 🎉 Package Size Decrease'
+            : '## ⚠️ Package Size Increase';
+
+      const packRows = changedPacks
+        .map((change) => {
+          const baseSize = change.baseSize
+            ? formatBytes(change.baseSize)
+            : 'New';
+          const sourceSize = change.sourceSize
+            ? formatBytes(change.sourceSize)
+            : 'Removed';
+          const sizeChange = formatBytesSigned(change.sizeChange);
+          return `| ${change.name} | ${baseSize} | ${sourceSize} | ${sizeChange} |`;
+        })
+        .join('\n');
+
+      messages.push(
+        `${heading}
+
+| 📦 Package | 📏 Base Size | 📏 Source Size | 📊 Size Change |
+| --- | --- | --- | --- |
+${packRows}`
+      );
+    }
+
+    return;
+  }
+
+  const totalSizeChange = comparison.packChanges
+    .filter((change) => change.sizeChange > 0)
+    .reduce((sum, change) => sum + change.sizeChange, 0);
+
+  if (totalSizeChange < threshold) {
+    return;
+  }
+
   const packWarnings = comparison.packChanges.filter(
-    (change) => change.exceedsThreshold && change.sizeChange > 0
+    (change) => change.sizeChange > 0
   );
 
   if (packWarnings.length > 0) {
@@ -22,7 +81,7 @@ export async function scanForBundleSize(
         const sourceSize = change.sourceSize
           ? formatBytes(change.sourceSize)
           : 'Removed';
-        const sizeChange = formatBytes(change.sizeChange);
+        const sizeChange = formatBytesSigned(change.sizeChange);
         return `| ${change.name} | ${baseSize} | ${sourceSize} | ${sizeChange} |`;
       })
       .join('\n');
diff --git a/src/packs.ts b/src/packs.ts
index 06d05cb..5955e37 100644
--- a/src/packs.ts
+++ b/src/packs.ts
@@ -175,7 +175,8 @@ export function comparePackSizes(
     const sourceSize = sourcePack?.size ?? null;
 
     const sizeChange = (sourceSize ?? 0) - (baseSize ?? 0);
-    const exceedsThreshold = sizeChange >= threshold;
+    const exceedsThreshold =
+      threshold === -1 ? sizeChange !== 0 : sizeChange >= threshold;
 
     packChanges.push({
       name: packName,
diff --git a/test/checks/__snapshots__/bundle-size_test.ts.snap b/test/checks/__snapshots__/bundle-size_test.ts.snap
new file mode 100644
index 0000000..f44ec1f
--- /dev/null
+++ b/test/checks/__snapshots__/bundle-size_test.ts.snap
@@ -0,0 +1,64 @@
+// Vitest Snapshot v1, https://vitest.dev/guide/snapshot.html
+
+exports[`scanForBundleSize > should celebrate size decrease when threshold is -1 1`] = `
+[
+  "## 🎉 Package Size Decrease
+
+| 📦 Package | 📏 Base Size | 📏 Source Size | 📊 Size Change |
+| --- | --- | --- | --- |
+| my-package | 200 kB | 100 kB | -100 kB |",
+]
+`;
+
+exports[`scanForBundleSize > should report no bundle size change with threshold=-1 when diff is 0 1`] = `
+[
+  "## 📦 Package Bundle Size
+
+No bundle size changes.",
+]
+`;
+
+exports[`scanForBundleSize > should show both decreases and increases when threshold is -1 1`] = `
+[
+  "## 📦 Package Bundle Size Changes
+
+| 📦 Package | 📏 Base Size | 📏 Source Size | 📊 Size Change |
+| --- | --- | --- | --- |
+| pkg-b | 50 kB | 150 kB | +100 kB |
+| pkg-a | 200 kB | 100 kB | -100 kB |",
+]
+`;
+
+exports[`scanForBundleSize > should show only increases when threshold is -1 and no decreases 1`] = `
+[
+  "## ⚠️ Package Size Increase
+
+| 📦 Package | 📏 Base Size | 📏 Source Size | 📊 Size Change |
+| --- | --- | --- | --- |
+| my-package | 100 kB | 200 kB | +100 kB |",
+]
+`;
+
+exports[`scanForBundleSize > should warn about an increase even when a decrease in another package cancels it out in total 1`] = `
+[
+  "## ⚠️ Package Size Increase
+
+These packages exceed the size increase threshold of 50 kB:
+
+| 📦 Package | 📏 Base Size | 📏 Source Size | 📈 Size Change |
+| --- | --- | --- | --- |
+| pkg-b | 50 kB | 150 kB | +100 kB |",
+]
+`;
+
+exports[`scanForBundleSize > should warn about size increase exceeding threshold 1`] = `
+[
+  "## ⚠️ Package Size Increase
+
+These packages exceed the size increase threshold of 50 kB:
+
+| 📦 Package | 📏 Base Size | 📏 Source Size | 📈 Size Change |
+| --- | --- | --- | --- |
+| my-package | 100 kB | 200 kB | +100 kB |",
+]
+`;
diff --git a/test/checks/bundle-size_test.ts b/test/checks/bundle-size_test.ts
new file mode 100644
index 0000000..d94f5e6
--- /dev/null
+++ b/test/checks/bundle-size_test.ts
@@ -0,0 +1,167 @@
+import {describe, expect, it} from 'vitest';
+import {scanForBundleSize} from '../../src/checks/bundle-size.js';
+import type {PackInfo} from '../../src/packs.js';
+
+function makePack(packageName: string, size: number): PackInfo {
+  return {
+    name: `${packageName}-1.0.0.tgz`,
+    packageName,
+    path: `/tmp/${packageName}-1.0.0.tgz`,
+    size
+  };
+}
+
+describe('scanForBundleSize', () => {
+  it('should do nothing when no packs are provided', async () => {
+    const messages: string[] = [];
+    await scanForBundleSize(messages, [], [], 50000);
+    expect(messages).toHaveLength(0);
+  });
+
+  it('should report no bundle size change when diff is 0', async () => {
+    const messages: string[] = [];
+    const basePacks = [makePack('my-package', 100000)];
+    const sourcePacks = [makePack('my-package', 100000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, 50000);
+
+    expect(messages).toHaveLength(0);
+  });
+
+  it('should report no bundle size change with threshold=-1 when diff is 0', async () => {
+    const messages: string[] = [];
+    const basePacks = [makePack('my-package', 100000)];
+    const sourcePacks = [makePack('my-package', 100000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, -1);
+
+    expect(messages).toHaveLength(1);
+    expect(messages[0]).toContain('No bundle size changes');
+    expect(messages).toMatchSnapshot();
+  });
+
+  it('should not report anything when diff is 0 and threshold is not -1', async () => {
+    const messages: string[] = [];
+    const basePacks = [makePack('my-package', 100000)];
+    const sourcePacks = [makePack('my-package', 100000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, 50000);
+
+    expect(messages).toHaveLength(0);
+  });
+
+  it('should never warn about a pure size decrease, no matter how large', async () => {
+    const messages: string[] = [];
+    // sizeChange is signed: (sourceSize - baseSize) = negative for a shrink
+    // A massive decrease should never cross a positive threshold
+    const basePacks = [makePack('my-package', 1000000)];
+    const sourcePacks = [makePack('my-package', 1)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, 50000);
+
+    expect(messages).toHaveLength(0);
+  });
+
+  it('should warn even when net total change is negative due to a large decrease masking an increase', async () => {
+    const messages: string[] = [];
+    // pkg-a shrinks by 500 KB, pkg-b grows by 100 KB → net = -400 KB
+    // Without filtering to increases only, -400 KB < 50 KB threshold → silent (wrong)
+    const basePacks = [makePack('pkg-a', 500000), makePack('pkg-b', 50000)];
+    const sourcePacks = [makePack('pkg-a', 0), makePack('pkg-b', 150000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, 50000);
+
+    expect(messages).toHaveLength(1);
+    expect(messages[0]).toContain('pkg-b');
+    expect(messages[0]).not.toContain('pkg-a');
+  });
+
+  it('should sum multiple increases when checking against the threshold', async () => {
+    const messages: string[] = [];
+    // Each increase is 30 KB (below the 50 KB threshold individually)
+    // but combined they are 60 KB (above threshold) → should warn
+    const basePacks = [makePack('pkg-a', 100000), makePack('pkg-b', 100000)];
+    const sourcePacks = [makePack('pkg-a', 130000), makePack('pkg-b', 130000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, 50000);
+
+    expect(messages).toHaveLength(1);
+    expect(messages[0]).toContain('pkg-a');
+    expect(messages[0]).toContain('pkg-b');
+  });
+
+  it('should warn about size increase exceeding threshold', async () => {
+    const messages: string[] = [];
+    const basePacks = [makePack('my-package', 100000)];
+    const sourcePacks = [makePack('my-package', 200000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, 50000);
+
+    expect(messages).toMatchSnapshot();
+  });
+
+  it('should not warn about size increase below threshold', async () => {
+    const messages: string[] = [];
+    const basePacks = [makePack('my-package', 100000)];
+    const sourcePacks = [makePack('my-package', 120000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, 50000);
+
+    expect(messages).toHaveLength(0);
+  });
+
+  it('should warn about an increase even when a decrease in another package cancels it out in total', async () => {
+    const messages: string[] = [];
+    // pkg-a shrinks by 100 KB, pkg-b grows by 100 KB → net = 0, but pkg-b exceeds threshold
+    const basePacks = [makePack('pkg-a', 200000), makePack('pkg-b', 50000)];
+    const sourcePacks = [makePack('pkg-a', 100000), makePack('pkg-b', 150000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, 50000);
+
+    expect(messages).toHaveLength(1);
+    expect(messages[0]).toContain('pkg-b');
+    expect(messages[0]).not.toContain('pkg-a');
+    expect(messages).toMatchSnapshot();
+  });
+
+  it('should not report no-change when changes exist but are below threshold', async () => {
+    const messages: string[] = [];
+    const basePacks = [makePack('my-package', 100000)];
+    const sourcePacks = [makePack('my-package', 120000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, 50000);
+
+    expect(messages).toHaveLength(0);
+  });
+
+  it('should celebrate size decrease when threshold is -1', async () => {
+    const messages: string[] = [];
+    const basePacks = [makePack('my-package', 200000)];
+    const sourcePacks = [makePack('my-package', 100000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, -1);
+
+    expect(messages).toMatchSnapshot();
+  });
+
+  it('should show both decreases and increases when threshold is -1', async () => {
+    const messages: string[] = [];
+    const basePacks = [makePack('pkg-a', 200000), makePack('pkg-b', 50000)];
+    const sourcePacks = [makePack('pkg-a', 100000), makePack('pkg-b', 150000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, -1);
+
+    expect(messages).toHaveLength(1);
+    expect(messages).toMatchSnapshot();
+  });
+
+  it('should show only increases when threshold is -1 and no decreases', async () => {
+    const messages: string[] = [];
+    const basePacks = [makePack('my-package', 100000)];
+    const sourcePacks = [makePack('my-package', 200000)];
+
+    await scanForBundleSize(messages, basePacks, sourcePacks, -1);
+
+    expect(messages).toMatchSnapshot();
+  });
+});