AG-UI DevTools

Inspect, validate, and replay AG-UI and LangGraph Platform agent streams. No SDK, no code change, no data leaves your browser.

Debug agent streams on the wire, not in your app AG-UI is an event protocol over server-sent events, and LangGraph Platform streams its runs the same way. When an agent run misbehaves, the Network panel shows you an opaque text/event-stream and console.log shows you what your app thinks happened. AG-UI DevTools shows you the wire: every event in order, grouped into runs, with the protocol violations named and located. Why the existing options do not work • Chrome's Network panel gives you raw data: lines. No decoding, no run grouping, no state reconstruction, no validation. • In-app inspectors ship inside your bundle, are tied to one framework, and cannot help an Angular, Vue, or vanilla AG-UI app at all. • Editor extensions need a runtime in dev mode, so they go dark exactly where bugs are hardest to reproduce. This is a wire-level tool. It attaches to the protocol instead of the framework. What it does • Captures agent streams from fetch, XMLHttpRequest, and EventSource • Decodes SSE framing and groups events into runs and threads • Reads LangGraph Platform runs too — every frame keeps its LangGraph event name, subgraphs fold into child runs, and the panel shows the AG-UI events each frame implies, so one timeline covers both • Validates protocol invariants and names each violation at the event that caused it • Reconstructs messages, tool-call trees, and state with full RFC 6902 patch history • Measures time to first token, run duration, and streaming stalls — in the run table and on the timeline • Inspects generative UI — A2UI and json-render surfaces as component trees, flagging types the app's catalog lacks • Records and replays — export a capture as .agui.jsonl and reopen it anywhere • Turns a run into a test — any capture exports as a TypeScript fixture module, and a LangGraph run as a ready-to-run Threadplane spec that replays it through @threadplane/langgraph's MockAgentTransport • Names the CopilotKit runtime and the agents it reports, read from the /info response the page already fetches • Flags an enabled tab in the toolbar once it speaks AG-UI or LangGraph Platform Privacy, stated as fact This tool sits where prompts and completions flow, so its posture is not a matter of trust: • No network egress. Ever. No remote host permissions, no fetch from the service worker or the panel, no telemetry, no update pings, no crash reporting. • Opt in per origin. The extension ships inert. Only localhost, 127.0.0.1, and 0.0.0.0 are registered up front; every other origin takes an explicit click. • Nothing on disk by default. Capture lives in memory with a chrome.storage.session mirror that Chrome clears when the browser closes. • Headers are never captured except content-type. Authorization headers and cookies are never read, never stored, never exported. • Redaction on export for bug-report bundles: text, reasoning, tool arguments, tool results and state values are replaced in the events that carry them — field by field on a LangGraph capture; see the privacy policy for the exceptions — while structure, types, ordering, sizes and timings survive, which is what a protocol bug report actually needs. • One switch changes what a page does, and it is off. Developer mode is per origin, off by default, and offered only where capture is enabled. With it on, the panel can hand an app built to accept one — a Threadplane development build, 0.3.0 or later — a script for its next agent run: events the app plays through its own code. It is data, never code the extension runs, and on any other app it does nothing. Every claim above is checkable by reading the built manifest.json, and the repository's build verification asserts them on every commit. Open source MIT licensed. Source, issues, and the full specification: https://github.com/blove/ag-ui-chrome-extension