[BUG] LoadArtifactsTool incorrectly classifies image/svg+xml as Gemini-supported, causing 400 INVALID_ARGUMENT #5693

🔴 Required Information

Describe the Bug:

_is_inline_mime_type_supported in LoadArtifactsTool returns True for image/svg+xml via the image/ prefix match at src/google/adk/tools/load_artifacts_tool.py:32-36, so SVG artifacts get forwarded to Gemini as inline image data. Gemini rejects every SVG MIME variant with 400 INVALID_ARGUMENT - Unsupported MIME type: image/svg+xml, instead of being text-converted like CSV / JSON / XML are since #4028.

Steps to Reproduce:

1. Install: pip install "google-adk" "google-genai>=1.72,<2"

2. Save any small SVG file as logo.svg.

3. Run this script:

   from google import genai
   from google.genai import types
   
   client = genai.Client(api_key="<YOUR_KEY>")
   with open("logo.svg", "rb") as f:
       part = types.Part.from_bytes(data=f.read(), mime_type="image/svg+xml")
   
   client.models.generate_content(
       model="gemini-2.5-flash",
       contents=["Describe this.", part],
   )

4. Observe the 400. The same code path is exercised inside ADK whenever LoadArtifactsTool encounters an artifact with mime_type='image/svg+xml': _is_inline_mime_type_supported returns True, _as_safe_part_for_llm returns the raw artifact, and the request reaches Gemini as inline image data.

Expected Behavior:

LoadArtifactsTool should recognise that image/svg+xml is not actually accepted by Gemini as inline image data, and route the artifact through the existing text-fallback path (the same one used for application/csv / application/json / application/xml since #4028). The SVG markup would then be delivered to the model as a text Part.

Observed Behavior:

The artifact is forwarded as inline image data and the Gemini API returns:

google.genai.errors.ClientError: 400 INVALID_ARGUMENT.
{'error': {'code': 400, 'message': 'Unsupported MIME type: image/svg+xml', 'status': 'INVALID_ARGUMENT'}}

The agent run aborts with this error instead of degrading gracefully.

Environment Details:

• ADK Library Version (pip show google-adk): main (fd8b4929 at time of testing)
• Desktop OS: macOS (Darwin 25.4.0)
• Python Version: 3.13 (also reproduces on 3.11)

Model Information:

• Are you using LiteLLM: No (reproduced against the native Gemini path; the SDK that fails is the google-genai client used by ADK)
• Which model is being used: gemini-2.5-flash

🟡 Optional Information

Regression:

Not a regression. The MIME validation in load_artifacts_tool.py was added in fdc98d5c (close #4028, 2026-01-15) to convert unsupported artifacts to text rather than crashing on them. SVG slipped through the image/ prefix check at that time and was never explicitly handled.

Additional Context:

Tested matrix against gemini-2.5-flash via google-genai==1.75.0 to confirm image/svg+xml is the only sub-case that needs special handling today:

So audio/* and video/* don't have the same gap; only the image/ prefix has the SVG sub-case.

Proposed fix:

Add an explicit denylist for subtypes that match a supported prefix but that Gemini still rejects, and route SVG through the existing text-fallback path. Same shape as the #4028 fix:

_GEMINI_UNSUPPORTED_INLINE_SUBTYPES = frozenset({'image/svg+xml'})

_TEXT_LIKE_MIME_TYPES = frozenset({
    'application/csv',
    'application/json',
    'application/xml',
    'image/svg+xml',  # XML-based; falls through here after the denylist above
})

def _is_inline_mime_type_supported(mime_type):
    normalized = _normalize_mime_type(mime_type)
    if not normalized:
        return False
    if normalized in _GEMINI_UNSUPPORTED_INLINE_SUBTYPES:
        return False
    return normalized.startswith(_GEMINI_SUPPORTED_INLINE_MIME_PREFIXES) or (
        normalized in _GEMINI_SUPPORTED_INLINE_MIME_TYPES
    )

PR with this fix plus a test_load_artifacts_converts_svg_to_text mirroring the existing CSV test: #5694.

Related:

• load_artifact for not natively supported types shouldn't explode with "Unsupported MIME Type" #4028 closed by fdc98d5c. Same shape of bug for application/csv. This issue is the missed sub-case under the image/ prefix.

Minimal Reproduction Code:

from google import genai
from google.genai import types

client = genai.Client(api_key="...")
with open("any.svg", "rb") as f:
    part = types.Part.from_bytes(data=f.read(), mime_type="image/svg+xml")

client.models.generate_content(
    model="gemini-2.5-flash",
    contents=["Describe this.", part],
)
# google.genai.errors.ClientError: 400 INVALID_ARGUMENT.
# 'Unsupported MIME type: image/svg+xml'

How often has this issue occurred?:

• Always (100%) when an artifact with mime_type='image/svg+xml' is loaded via LoadArtifactsTool and sent to a Gemini model.