AG-UI Event Lab

Event stream debugger

Make agent streams predictable.

Paste raw AG-UI SSE, JSONL or JSON. Catch missing event fields, broken run and message sequences, tool-call lifecycle mistakes, malformed JSON Patch operations and deprecated event types before they reach your frontend.

AG-UI SSE / JSONL

Validation report

Why this tool exists

A valid event can still form an invalid stream.

AG-UI is an open, event-based protocol that connects agent backends to user-facing applications. It can travel over Server-Sent Events, WebSockets or other transports. The protocol defines events for runs, text messages, tool calls, shared state, activities, reasoning and custom data.

Field validation alone cannot tell whether a frontend can consume a stream safely. A text delta may reference a message that never started. Tool arguments may arrive after the tool call ended. A run may finish with identifiers different from those used at start. This validator keeps lifecycle state across the complete pasted stream.

Checks included

  • Raw SSE data: blocks, JSON Lines, JSON arrays and single events.
  • Current AG-UI event names and required field types.
  • Run start, terminal event and thread/run identifier matching.
  • Text message, tool call, step and reasoning start/end sequences.
  • RFC 6902 operation, path, value and from checks for state/activity patches.
  • Warnings for legacy THINKING_* events deprecated before 1.0.
  • An ordered event timeline for fast debugging.

This is an independent structural linter. It does not execute tools, apply state, verify transport headers or replace testing against your actual AG-UI client SDK.

Practical workflow

Debug producer output before frontend state mutates.

  1. Capture the stream. Copy SSE response text or log one JSON event per line.
  2. Check event fields. Fix unknown event names, missing IDs and invalid deltas.
  3. Follow the lifecycle. Match every start/content/end sequence and one terminal run event.
  4. Review patches. Test JSON Patch operations against representative client state.
  5. Replay in your SDK. Confirm client-specific transforms such as chunk expansion.

Focused references

Fix the stream, not just the symptom.

AG-UI event validator guide

Understand accepted input formats and the difference between event schema and stream semantics.

Read the guide →

AG-UI SSE parser

Learn how data blocks, blank-line boundaries and JSON payloads become ordered events.

Open the parser guide →

AG-UI stream errors

Debug messages, tool calls, run IDs, patches and deprecated thinking events.

Browse errors →

FAQ

Before you ship.

Which formats can I paste?

Raw SSE with JSON in data lines, JSONL, a JSON array or one JSON event.

Does this use the official SDK?

The field rules track the public TypeScript core schemas. The browser checker is an independent implementation and clearly separates its additional lifecycle diagnostics.

Why are THINKING events warnings?

The official SDK marks THINKING_* events deprecated and recommends REASONING_* replacements before version 1.0.

Is valid JSON Patch guaranteed to apply?

No. The checker validates operation shape and pointer syntax. Application still depends on your current state document.

Is this affiliated with AG-UI or CopilotKit?

No. AG-UI Event Lab is an independent developer utility based on public documentation.