mozilla/pdf.js · warning · Error

No ML.

Error message

No ML.

What it means

Thrown by StampEditor.mlGuessAltText when this._uiManager.mlManager is null/undefined. The ML manager is an optional, host-provided integration (e.g., Firefox's built-in model); when it is not registered, alt-text guessing is unavailable and the method aborts rather than silently returning garbage.

Source

Thrown at src/display/editor/stamp.js:165

      });
      try {
        // The alt-text dialog isn't opened but we still want to guess the alt
        // text.
        this.mlGuessAltText();
      } catch {}
    }

    this.div.focus();
  }

  async mlGuessAltText(imageData = null, updateAltTextData = true) {
    if (this.hasAltTextData()) {
      return null;
    }

    const { mlManager } = this._uiManager;
    if (!mlManager) {
      throw new Error("No ML.");
    }
    if (!(await mlManager.isEnabledFor("altText"))) {
      throw new Error("ML isn't enabled for alt text.");
    }
    const { data, width, height } =
      imageData ||
      this.copyCanvas(null, null, /* createImageData = */ true).imageData;
    const response = await mlManager.guess({
      name: "altText",
      request: {
        data,
        width,
        height,
        channels: data.length / (width * height),
      },
    });
    if (!response) {
      throw new Error("No response from the AI service.");

View on GitHub (pinned to 5903d58d58)

Solutions

1. Check for mlManager availability before calling: if (!editor._uiManager.mlManager) return null.
2. Register an mlManager implementation on the UI manager if you want the feature.
3. Feature-detect and hide the 'Guess alt text' UI when no mlManager is present.

Example fix

// before
const alt = await stampEditor.mlGuessAltText(imageData);

// after
if (!stampEditor._uiManager.mlManager) {
  // alt-text ML is not available in this build/host
  return null;
}
const alt = await stampEditor.mlGuessAltText(imageData);

function canGuessAltText(editor) {
  return !!editor._uiManager?.mlManager;
}
if (canGuessAltText(stampEditor)) {
  return stampEditor.mlGuessAltText(imageData);
}

const hasMlManager = (e): boolean => !!e?._uiManager?.mlManager;

null

When it happens

Trigger: Calling mlGuessAltText in a generic/embedding context where no mlManager was passed to the editor UI manager; calling it before the host wired up the ML integration.

Common situations: Using pdfjs-dist outside Firefox and trying to use alt-text guessing; calling the API in tests without stubbing mlManager; feature gated off by the host application.

Related errors

• ML isn't enabled for alt text.
• XFA: Cannot save new annotations.
• extractPages: partial pageIndices cannot be combined with in
• extractPages: invalid page index.
• extractPages: overlapping pageIndices.

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/8f503899282d1b10. Report an issue: GitHub.