Rendering Markdown in Phoenix Tool Outputs: Any Solutions?

Fernando O. · 2025-09-12T11:38:34.433Z

Hi everyone, We’re using Phoenix on our own servers, with traces sent via OpenTelemetry. We’d like to display the output of a tool call with Markdown formatting (lists, headings, etc.), but so far it only shows up as plain text. Is there any way to have Phoenix render Markdown in tool outputs? Or is this simply not supported yet in the open-source version? Thanks in advance!

5 comments

· Sorted by Oldest

RunLLM
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Phoenix supports Markdown rendering for text outputs, including tool outputs, in the UI. A Markdown/text toggle is available in relevant viewers, allowing you to switch between plain text and Markdown rendering for outputs that contain Markdown syntax. This feature is present in the open-source version and is not limited to proprietary or cloud editions. See the implementation and screenshots in <https://github.com/Arize-ai/phoenix/pull/2703|feat(ui): markdown highlighting> and related discussion in <https://github.com/Arize-ai/phoenix/issues/5112|issue #5112>. If you are not seeing Markdown rendering, ensure you are using a recent version of Phoenix and check for the Markdown toggle in the output viewer. If the toggle is missing or not working for tool outputs, it may be a UI bug or a limitation in how your traces are structured. Would you like more detail on how to enable or troubleshoot this feature? Sources: - <https://github.com/Arize-ai/phoenix/pull/2703|feat(ui): markdown highlighting> - <https://github.com/Arize-ai/phoenix/issues/5112|issue #5112>
💡 Hint: Mention RunLLM in the thread for followups.
Fernando O.
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I don't think those solutions work on spans of type tool. In fact, they are for type llm on roles "system" and "assistant". Our version is 11.2.2
Fernando O.
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I'm manually setting up spans with the corresponding attibutes like "openinference.span.kind": "TOOL". In the case of output, I'm just using "output.value" and "output.mime_type". But the only two values of the class OpenInferenceMimeTypeValues of openinference module are "text/plain" and "application/json", there is no "text/markdown" value (I'm also tried to force this value in case Phoenix can understand it).
Fernando O.
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Any update about it? I suspect that it is not possible right now, but I'm not completely sure.
Srilakshmi
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Hi Fernando, sorry for the delay on this. looking into this right now

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