NousResearch/hermes-agent · error · ValueError

image input 'data' must be bytes

Error message

image input 'data' must be bytes

What it means

Error "image input 'data' must be bytes" thrown in NousResearch/hermes-agent.

Source

Thrown at agent/plugin_llm.py:538

        except (TypeError, ValueError):
            schema_text = str(json_schema)
        header = f"{header}\n\nJSON schema:\n{schema_text}"
    user_parts.append({"type": "text", "text": header})

    for block in inputs:
        norm = _normalize_input_block(block)
        if norm["type"] == "text":
            user_parts.append({"type": "text", "text": norm["text"]})
        elif norm["type"] == "image":
            if norm.get("url"):
                user_parts.append({
                    "type": "image_url",
                    "image_url": {"url": norm["url"]},
                })
            else:
                data = norm.get("data") or b""
                if not isinstance(data, (bytes, bytearray)):
                    raise ValueError("image input 'data' must be bytes")
                b64 = base64.b64encode(data).decode("ascii")
                mime = norm.get("mime_type") or "image/png"
                user_parts.append({
                    "type": "image_url",
                    "image_url": {"url": f"data:{mime};base64,{b64}"},
                })

    messages.append({"role": "user", "content": user_parts})
    return messages


# ---------------------------------------------------------------------------
# JSON parsing
# ---------------------------------------------------------------------------


_FENCE_RE = re.compile(r"```(?:json)?\s*(.+?)```", re.DOTALL | re.IGNORECASE)

View on GitHub (pinned to c896c09c42)

Solutions

1. Pass image 'data' as bytes, not a string or other type.
2. Encode the image correctly in the plugin before building the block.

When it happens

Trigger: Thrown at agent/plugin_llm.py:538 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of NousResearch/hermes-agent@c896c09c42 (2026-08-14). Data as JSON: /api/errors/ee9531b41891fa74. Report an issue: GitHub.