Synchronization conversation and codecs CLI session logs are not readable by default. This is a problem when your agent does something unexpected.
what is it: Euphony is an open-source browser tool from OpenAI that renders Harmony JSON/JSONL files and codecs session logs as structured, interactive conversation timelines.
The problem: AI agents running on Harmony Format data generate deeply nested JSON with role tokens, channel markers, and interleaved tool calls. Codex CLI writes a rollout JSONL file to disk after each session. Neither format is designed for human inspection. Debugging agent behavior means scrolling through hundreds of lines of raw structured data with no visual hierarchy.
Solution: Euphony loads this data from a URL, local file, or clipboard paste and presents it as a readable timeline. Filter by role, recipient, or content type using JMESPath. Inspect the message metadata. Edit the browser. Translate using your own OpenAI API key. All processing remains client-side in default front-end mode.
What makes it different?: It ships as an embeddable web component, so you can drop an interactive viewer with a single custom element in React, Vue, Svelte, or plain HTML. No need to create viewers from scratch. The optional FastAPI backend adds Harmony tokenization rendering, which shows exactly how the interaction will be tokenized before reaching the model.
Key Features:
Load from the clipboard, a local file, or a public HTTPS URL.
Filtering by JMESPath role, recipient, and content type
Metadata inspection panel for annotated datasets
Browser editing, focus mode, and grid view
Embeddable Web Components, Apache 2.0 License
Who is it for?: AI engineers working with gpt-oss models, Codex CLI, or Harmony format datasets for training, evaluation, or agent pipelines.
Agent debugging requires proper tooling for a while. Euphony is a small but real step towards this.