# `ClaudeAgentSDK.Streaming.EventParser`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/streaming/event_parser.ex#L1)

Parses streaming events from Claude CLI's `--include-partial-messages` output.

Handles all Server-Sent Events (SSE) types from the Anthropic Messages API:
- `message_start` - Message initialization with metadata
- `content_block_start` - Content block (text/tool_use/thinking) starts
- `content_block_delta` - Incremental content updates (THE CORE STREAMING EVENT)
  - `text_delta` - Character-by-character text streaming
  - `input_json_delta` - Tool input JSON being built
  - `thinking_delta` - Extended thinking content (Sonnet 4.5+)
- `content_block_stop` - Content block complete
- `message_delta` - Message-level metadata updates
- `message_stop` - Message complete

## References
- https://docs.anthropic.com/en/api/messages-streaming

# `accumulated_text`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/streaming/event_parser.ex#L23)

```elixir
@type accumulated_text() :: String.t()
```

# `event`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/streaming/event_parser.ex#L22)

```elixir
@type event() :: map()
```

# `parse_buffer`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/streaming/event_parser.ex#L257)

```elixir
@spec parse_buffer(String.t(), accumulated_text()) ::
  {:ok, [event()], String.t(), accumulated_text()}
```

Parses a buffer of newline-delimited JSON and returns parsed events.

Handles partial JSON lines by returning the unparsed remainder.

## Parameters
- `buffer` - String buffer containing newline-delimited JSON
- `accumulated_text` - Current accumulated text for the message

## Returns
`{:ok, events, remaining_buffer, new_accumulated_text}`

## Examples

    buffer = ~s({"type":"message_start","message":{"model":"sonnet"}}\n{"type":"content_block_delta","delta":{"type":"text_delta","text":"Hi"}}\npartial)
    {:ok, events, remaining, accumulated} = EventParser.parse_buffer(buffer, "")

    # events will contain both parsed events
    # remaining will be "partial" (incomplete JSON line)
    # accumulated will be "Hi" (from text_delta)

# `parse_event`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/streaming/event_parser.ex#L73)

```elixir
@spec parse_event(map(), accumulated_text()) :: {:ok, [event()], accumulated_text()}
```

Parses a single streaming event from Claude CLI output.

Returns `{:ok, [events], new_accumulated_text}` where:
- `events` - List of parsed event maps (may be empty for unknown events)
- `new_accumulated_text` - Updated accumulated text for current message

## Parameters
- `raw_event` - Decoded JSON map from CLI stdout
- `accumulated_text` - Current accumulated text for this message

## Event Types Returned

### Text Streaming (primary use case)
- `%{type: :text_delta, text: "...", accumulated: "..."}` - Character chunk + full text so far

### Message Lifecycle
- `%{type: :message_start, model: "..."}` - Message begins
- `%{type: :message_stop, final_text: "..."}` - Message complete

### Content Blocks
- `%{type: :text_block_start}` - Text content block starts
- `%{type: :content_block_stop, final_text: "..."}` - Block complete
- `%{type: :tool_use_start, name: "...", id: "..."}` - Tool call starts
- `%{type: :thinking_start}` - Thinking block starts (Sonnet 4.5+)

### Tool & Thinking
- `%{type: :tool_input_delta, json: "..."}` - Partial tool input JSON
- `%{type: :thinking_delta, thinking: "..."}` - Thinking content chunk

### Metadata
- `%{type: :message_delta, stop_reason: "...", stop_sequence: "..."}` - Final metadata

## Examples

    # Text delta (most common event)
    {:ok, [%{type: :text_delta, text: "Hello", accumulated: "Hello"}], "Hello"} =
      EventParser.parse_event(%{"type" => "content_block_delta", "delta" => %{"type" => "text_delta", "text" => "Hello"}}, "")

    # Message start
    {:ok, [%{type: :message_start, model: "claude-sonnet-4-5"}], ""} =
      EventParser.parse_event(%{"type" => "message_start", "message" => %{"model" => "claude-sonnet-4-5"}}, "")

    # Unknown event (ignored gracefully)
    {:ok, [], "existing text"} =
      EventParser.parse_event(%{"type" => "unknown_event"}, "existing text")

---

*Consult [api-reference.md](api-reference.md) for complete listing*