BoundaryML/baml · error · Error

Pdf is not a URL

Error message

Pdf is not a URL

What it means

TypeScript client state guard: asUrl() was called on a BamlPdf whose internal type is 'base64', not 'url'. BamlPdf is a tagged union of the two representations; the accessor for the wrong tag throws rather than return base64 payload bytes where a URL is expected.

Source

Thrown at engine/language_client_typescript/typescript_src/pdf.ts:69

    const response = await fetch(url);
    const blob = await response.blob();
    return BamlPdf.fromBlob(blob);
  }

  /**
   * Check if the pdf is stored as a URL
   */
  isUrl(): boolean {
    return this.type === "url";
  }

  /**
   * Get the URL of the pdf if it's stored as a URL
   * @throws Error if the pdf is not stored as a URL
   */
  asUrl(): string {
    if (!this.isUrl()) {
      throw new Error("Pdf is not a URL");
    }
    return this.content;
  }

  /**
   * Get the base64 data and media type if the pdf is stored as base64
   * @returns [base64Data, mediaType]
   * @throws Error if the pdf is not stored as base64
   */
  asBase64(): [string, string] {
    if (this.type !== "base64") {
      throw new Error("Pdf is not base64");
    }
    return [this.content, this.mediaType || ""];
  }

  /**
   * Convert the pdf to a JSON representation

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Guard with pdf.isUrl() before calling asUrl()
2. Construct the Pdf from a URL (Pdf.fromUrl(...)) when URL access is required
3. Branch on storage type and handle the base64 case with asBase64()

Example fix

// before
const url = pdf.asUrl(); // throws for base64 pdf
// after
if (pdf.isUrl()) {
  const url = pdf.asUrl();
} else {
  const [b64, mediaType] = pdf.asBase64();
}

if (!pdf.isUrl()) { /* handle base64 branch */ }

const isUrlPdf = (p) => p.isUrl();

try { const url = pdf.asUrl(); }
catch { const [b64, mt] = pdf.asBase64(); }

When it happens

Trigger: Calling pdf.asUrl() on a Pdf constructed from base64 (fromBase64) or another non-URL source, where isUrl() is false.

Common situations: Displaying or sharing PDF links while the document was inlined as base64 (common when passing file bytes to LLMs); mixing URL-loaded and byte-loaded documents in the same code path.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

• BAML internal error (AWSBedrock): Pdf file should have been
• Audio is not a URL
• Image is not a URL
• Pdf is not base64
• BAML internal error (AWSBedrock): file should have been reso

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/1a8c7fece6c640a8. Report an issue: GitHub.