What is OpenAI Euphony?

Euphony is a web-based interactive tool developed by OpenAI for visualizing and exploring structured chat data. It is specifically designed to handle Harmony chat data and Codex session logs, transforming raw JSON or JSONL files into a readable conversation view. Users can inspect metadata, render markdown, and share specific messages or conversations via links.

How do you load data into the Euphony visualization tool?

You can load data into Euphony in three ways: by pasting JSON or JSONL content directly from your clipboard, by choosing a local file from your computer, or by providing a public URL that serves JSON or JSONL data. Once loaded, the tool processes the raw data into an easy-to-browse interface for analysis and review.

Is OpenAI Euphony open source?

Yes, Euphony is an open-source project hosted on GitHub. It provides portable and modular web components that developers can use to visualize structured chat data and Codex sessions in their own browsers. Being open source allows the community to inspect the code, contribute to its development, or host their own instances of the visualization tool.

What features does Euphony offer for debugging AI conversations?

Euphony includes advanced features like JMESPath filtering to query specific metadata, a token visualizer for the o200k_harmony tokenizer, and a focus mode to hide specific message roles like system or tool outputs. It also supports custom labels for evaluation annotations and can render HTML or markdown formulas directly within the chat bubbles for better readability.

What is the Harmony data format used by Euphony?

Harmony is the data format and tokenization system that Euphony is designed to visualize. This format supports various message roles, including user, assistant, system, and developer, as well as complex content types like code blocks and tool calls. Euphony allows users to see how this data is serialized and tokenized using specific Harmony renderers and tokenizers.

OpenAI Launches Euphony to Visualize Complex Codex Agent Session Logs

Agentic Coding

Evaluation

GPT

Performance

Published Apr 21, 2026

OpenAI launched Euphony, an open-source web tool designed to visualize structured chat data and Codex session logs. Users can load data by pasting JSON, uploading local files, or providing public URLs to transform raw logs into a navigable view. It supports Harmony, the company's standard for structured multi-turn interactions.

As autonomous engineering agents handle complex multi-file tasks, raw text logs become impossible to parse manually. Euphony fills this observability gap with a dedicated UI for inspecting tool calls and system prompts. This follows the shift toward production-grade agent infrastructure that prioritizes reliability and developer debugging.

You can use Euphony to filter datasets using JMESPath or inspect model tokenization via the integrated o200k_harmony visualizer. The tool is available for free as a hosted web app or can be integrated into custom workflows via its open-source repository on GitHub.

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Frequently asked questions

What is OpenAI Euphony?: Euphony is a web-based interactive tool developed by OpenAI for visualizing and exploring structured chat data. It is specifically designed to handle Harmony chat data and Codex session logs, transforming raw JSON or JSONL files into a readable conversation view. Users can inspect metadata, render markdown, and share specific messages or conversations via links.
How do you load data into the Euphony visualization tool?: You can load data into Euphony in three ways: by pasting JSON or JSONL content directly from your clipboard, by choosing a local file from your computer, or by providing a public URL that serves JSON or JSONL data. Once loaded, the tool processes the raw data into an easy-to-browse interface for analysis and review.
Is OpenAI Euphony open source?: Yes, Euphony is an open-source project hosted on GitHub. It provides portable and modular web components that developers can use to visualize structured chat data and Codex sessions in their own browsers. Being open source allows the community to inspect the code, contribute to its development, or host their own instances of the visualization tool.
What features does Euphony offer for debugging AI conversations?: Euphony includes advanced features like JMESPath filtering to query specific metadata, a token visualizer for the o200k_harmony tokenizer, and a focus mode to hide specific message roles like system or tool outputs. It also supports custom labels for evaluation annotations and can render HTML or markdown formulas directly within the chat bubbles for better readability.
What is the Harmony data format used by Euphony?: Harmony is the data format and tokenization system that Euphony is designed to visualize. This format supports various message roles, including user, assistant, system, and developer, as well as complex content types like code blocks and tool calls. Euphony allows users to see how this data is serialized and tokenized using specific Harmony renderers and tokenizers.