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RPC Mode

RPC mode enables headless operation of the coding agent via a JSON protocol over stdin/stdout. This is useful for embedding the agent in other applications, IDEs, or custom UIs.

Note for Node.js/TypeScript users: If you’re building a Node.js application, consider using AgentSession directly from @earendil-works/pi-coding-agent instead of spawning a subprocess. See src/core/agent-session.ts for the API. For a subprocess-based TypeScript client, see src/modes/rpc/rpc-client.ts.

Starting RPC Mode

Section titled “Starting RPC Mode”
Terminal window
pi --mode rpc [options]

Common options:

  • --provider <name>: Set the LLM provider (anthropic, openai, google, etc.)
  • --model <pattern>: Model pattern or ID (supports provider/id and optional :<thinking>)
  • --name <name> / -n <name>: Set the session display name at startup
  • --no-session: Disable session persistence
  • --session-dir <path>: Custom session storage directory

Protocol Overview

Section titled “Protocol Overview”
  • Commands: JSON objects sent to stdin, one per line
  • Responses: JSON objects with type: "response" indicating command success/failure
  • Events: Agent events streamed to stdout as JSON lines

All commands support an optional id field for request/response correlation. If provided, the corresponding response will include the same id.

Framing

Section titled “Framing”

RPC mode uses strict JSONL semantics with LF (\n) as the only record delimiter.

This matters for clients:

  • Split records on \n only
  • Accept optional \r\n input by stripping a trailing \r
  • Do not use generic line readers that treat Unicode separators as newlines

In particular, Node readline is not protocol-compliant for RPC mode because it also splits on U+2028 and U+2029, which are valid inside JSON strings.

Commands

Section titled “Commands”

Prompting

Section titled “Prompting”

prompt

Section titled “prompt”

Send a user prompt to the agent. The command response is emitted after the prompt is accepted, queued, or handled. Events continue streaming asynchronously after acceptance.

{"id": "req-1", "type": "prompt", "message": "Hello, world!"}

With images:

{"type": "prompt", "message": "What's in this image?", "images": [{"type": "image", "data": "base64-encoded-data", "mimeType": "image/png"}]}

During streaming: If the agent is already streaming, you must specify streamingBehavior to queue the message:

{"type": "prompt", "message": "New instruction", "streamingBehavior": "steer"}
  • "steer": Queue the message while the agent is running. It is delivered after the current assistant turn finishes executing its tool calls, before the next LLM call.
  • "followUp": Wait until the agent finishes. Message is delivered only when agent stops.

If the agent is streaming and no streamingBehavior is specified, the command returns an error.

Extension commands: If the message is an extension command (e.g., /mycommand), it executes immediately even during streaming. Extension commands manage their own LLM interaction via pi.sendMessage().

Input expansion: Skill commands (/skill:name) and prompt templates (/template) are expanded before sending/queueing.

Response:

{"id": "req-1", "type": "response", "command": "prompt", "success": true}

success: true means the prompt was accepted, queued, or handled immediately. success: false means the prompt was rejected before acceptance. Failures after acceptance are reported through the normal event and message stream, not as a second response for the same request id.

The images field is optional. Each image uses ImageContent format: {"type": "image", "data": "base64-encoded-data", "mimeType": "image/png"}.

steer

Section titled “steer”

Queue a steering message while the agent is running. It is delivered after the current assistant turn finishes executing its tool calls, before the next LLM call. Skill commands and prompt templates are expanded. Extension commands are not allowed (use prompt instead).

{"type": "steer", "message": "Stop and do this instead"}

With images:

{"type": "steer", "message": "Look at this instead", "images": [{"type": "image", "data": "base64-encoded-data", "mimeType": "image/png"}]}

The images field is optional. Each image uses ImageContent format (same as prompt).

Response:

{"type": "response", "command": "steer", "success": true}

See set_steering_mode for controlling how steering messages are processed.

follow_up

Section titled “follow_up”

Queue a follow-up message to be processed after the agent finishes. Delivered only when agent has no more tool calls or steering messages. Skill commands and prompt templates are expanded. Extension commands are not allowed (use prompt instead).

{"type": "follow_up", "message": "After you're done, also do this"}

With images:

{"type": "follow_up", "message": "Also check this image", "images": [{"type": "image", "data": "base64-encoded-data", "mimeType": "image/png"}]}

The images field is optional. Each image uses ImageContent format (same as prompt).

Response:

{"type": "response", "command": "follow_up", "success": true}

See set_follow_up_mode for controlling how follow-up messages are processed.

abort

Section titled “abort”

Abort the current agent operation.

{"type": "abort"}

Response:

{"type": "response", "command": "abort", "success": true}

new_session

Section titled “new_session”

Start a fresh session. Can be cancelled by a session_before_switch extension event handler.

{"type": "new_session"}

With optional parent session tracking:

{"type": "new_session", "parentSession": "/path/to/parent-session.jsonl"}

Response:

{"type": "response", "command": "new_session", "success": true, "data": {"cancelled": false}}

If an extension cancelled:

{"type": "response", "command": "new_session", "success": true, "data": {"cancelled": true}}

State

Section titled “State”

get_state

Section titled “get_state”

Get current session state.

{"type": "get_state"}

Response:

{
  "type": "response",
  "command": "get_state",
  "success": true,
  "data": {
    "model": {...},
    "thinkingLevel": "medium",
    "isStreaming": false,
    "isCompacting": false,
    "steeringMode": "all",
    "followUpMode": "one-at-a-time",
    "sessionFile": "/path/to/session.jsonl",
    "sessionId": "abc123",
    "sessionName": "my-feature-work",
    "autoCompactionEnabled": true,
    "messageCount": 5,
    "pendingMessageCount": 0
  }
}

The model field is a full Model object or null. The sessionName field is the display name set via set_session_name, or omitted if not set.

get_messages

Section titled “get_messages”

Get all messages in the conversation.

{"type": "get_messages"}

Response:

{
  "type": "response",
  "command": "get_messages",
  "success": true,
  "data": {"messages": [...]}
}

Messages are AgentMessage objects (see Message Types).

Model

Section titled “Model”

set_model

Section titled “set_model”

Switch to a specific model.

{"type": "set_model", "provider": "anthropic", "modelId": "claude-sonnet-4-20250514"}

Response contains the full Model object:

{
  "type": "response",
  "command": "set_model",
  "success": true,
  "data": {...}
}

cycle_model

Section titled “cycle_model”

Cycle to the next available model. Returns null data if only one model available.

{"type": "cycle_model"}

Response:

{
  "type": "response",
  "command": "cycle_model",
  "success": true,
  "data": {
    "model": {...},
    "thinkingLevel": "medium",
    "isScoped": false
  }
}

The model field is a full Model object.

get_available_models

Section titled “get_available_models”

List all configured models.

{"type": "get_available_models"}

Response contains an array of full Model objects:

{
  "type": "response",
  "command": "get_available_models",
  "success": true,
  "data": {
    "models": [...]
  }
}

Thinking

Section titled “Thinking”

set_thinking_level

Section titled “set_thinking_level”

Set the reasoning/thinking level for models that support it.

{"type": "set_thinking_level", "level": "high"}

Levels: "off", "minimal", "low", "medium", "high", "xhigh"

Note: "xhigh" is only supported by OpenAI codex-max models.

Response:

{"type": "response", "command": "set_thinking_level", "success": true}

cycle_thinking_level

Section titled “cycle_thinking_level”

Cycle through available thinking levels. Returns null data if model doesn’t support thinking.

{"type": "cycle_thinking_level"}

Response:

{
  "type": "response",
  "command": "cycle_thinking_level",
  "success": true,
  "data": {"level": "high"}
}

Queue Modes

Section titled “Queue Modes”

set_steering_mode

Section titled “set_steering_mode”

Control how steering messages (from steer) are delivered.

{"type": "set_steering_mode", "mode": "one-at-a-time"}

Modes:

  • "all": Deliver all steering messages after the current assistant turn finishes executing its tool calls
  • "one-at-a-time": Deliver one steering message per completed assistant turn (default)

Response:

{"type": "response", "command": "set_steering_mode", "success": true}

set_follow_up_mode

Section titled “set_follow_up_mode”

Control how follow-up messages (from follow_up) are delivered.

{"type": "set_follow_up_mode", "mode": "one-at-a-time"}

Modes:

  • "all": Deliver all follow-up messages when agent finishes
  • "one-at-a-time": Deliver one follow-up message per agent completion (default)

Response:

{"type": "response", "command": "set_follow_up_mode", "success": true}

Compaction

Section titled “Compaction”

compact

Section titled “compact”

Manually compact conversation context to reduce token usage.

{"type": "compact"}

With custom instructions:

{"type": "compact", "customInstructions": "Focus on code changes"}

Response:

{
  "type": "response",
  "command": "compact",
  "success": true,
  "data": {
    "summary": "Summary of conversation...",
    "firstKeptEntryId": "abc123",
    "tokensBefore": 150000,
    "estimatedTokensAfter": 32000,
    "details": {}
  }
}

estimatedTokensAfter is a heuristic estimate over the rebuilt message context immediately after compaction, not a provider-exact token count.

set_auto_compaction

Section titled “set_auto_compaction”

Enable or disable automatic compaction when context is nearly full.

{"type": "set_auto_compaction", "enabled": true}

Response:

{"type": "response", "command": "set_auto_compaction", "success": true}

Retry

Section titled “Retry”

set_auto_retry

Section titled “set_auto_retry”

Enable or disable automatic retry on transient errors (overloaded, rate limit, 5xx).

{"type": "set_auto_retry", "enabled": true}

Response:

{"type": "response", "command": "set_auto_retry", "success": true}

abort_retry

Section titled “abort_retry”

Abort an in-progress retry (cancel the delay and stop retrying).

{"type": "abort_retry"}

Response:

{"type": "response", "command": "abort_retry", "success": true}

Bash

Section titled “Bash”

bash

Section titled “bash”

Execute a shell command and add output to conversation context.

{"type": "bash", "command": "ls -la"}

Response:

{
  "type": "response",
  "command": "bash",
  "success": true,
  "data": {
    "output": "total 48\ndrwxr-xr-x ...",
    "exitCode": 0,
    "cancelled": false,
    "truncated": false
  }
}

If output was truncated, includes fullOutputPath:

{
  "type": "response",
  "command": "bash",
  "success": true,
  "data": {
    "output": "truncated output...",
    "exitCode": 0,
    "cancelled": false,
    "truncated": true,
    "fullOutputPath": "/tmp/pi-bash-abc123.log"
  }
}

How bash results reach the LLM:

The bash command executes immediately and returns a BashResult. Internally, a BashExecutionMessage is created and stored in the agent’s message state. This message does NOT emit an event.

When the next prompt command is sent, all messages (including BashExecutionMessage) are transformed before being sent to the LLM. The BashExecutionMessage is converted to a UserMessage with this format:

Ran `ls -la`
```
total 48
drwxr-xr-x ...
```

This means:

  1. Bash output is included in the LLM context on the next prompt, not immediately
  2. Multiple bash commands can be executed before a prompt; all outputs will be included
  3. No event is emitted for the BashExecutionMessage itself

abort_bash

Section titled “abort_bash”

Abort a running bash command.

{"type": "abort_bash"}

Response:

{"type": "response", "command": "abort_bash", "success": true}

Session

Section titled “Session”

get_session_stats

Section titled “get_session_stats”

Get token usage, cost statistics, and current context window usage.

{"type": "get_session_stats"}

Response:

{
  "type": "response",
  "command": "get_session_stats",
  "success": true,
  "data": {
    "sessionFile": "/path/to/session.jsonl",
    "sessionId": "abc123",
    "userMessages": 5,
    "assistantMessages": 5,
    "toolCalls": 12,
    "toolResults": 12,
    "totalMessages": 22,
    "tokens": {
      "input": 50000,
      "output": 10000,
      "cacheRead": 40000,
      "cacheWrite": 5000,
      "total": 105000
    },
    "cost": 0.45,
    "contextUsage": {
      "tokens": 60000,
      "contextWindow": 200000,
      "percent": 30
    }
  }
}

tokens contains assistant usage totals for the current session state. contextUsage contains the actual current context-window estimate used for compaction and footer display.

contextUsage is omitted when no model or context window is available. contextUsage.tokens and contextUsage.percent are null immediately after compaction until a fresh post-compaction assistant response provides valid usage data.

export_html

Section titled “export_html”

Export session to an HTML file.

{"type": "export_html"}

With custom path:

{"type": "export_html", "outputPath": "/tmp/session.html"}

Response:

{
  "type": "response",
  "command": "export_html",
  "success": true,
  "data": {"path": "/tmp/session.html"}
}

switch_session

Section titled “switch_session”

Load a different session file. Can be cancelled by a session_before_switch extension event handler.

{"type": "switch_session", "sessionPath": "/path/to/session.jsonl"}

Response:

{"type": "response", "command": "switch_session", "success": true, "data": {"cancelled": false}}

If an extension cancelled the switch:

{"type": "response", "command": "switch_session", "success": true, "data": {"cancelled": true}}

fork

Section titled “fork”

Create a new fork from a previous user message on the active branch. Can be cancelled by a session_before_fork extension event handler. Returns the text of the message being forked from.

{"type": "fork", "entryId": "abc123"}

Response:

{
  "type": "response",
  "command": "fork",
  "success": true,
  "data": {"text": "The original prompt text...", "cancelled": false}
}

If an extension cancelled the fork:

{
  "type": "response",
  "command": "fork",
  "success": true,
  "data": {"text": "The original prompt text...", "cancelled": true}
}

clone

Section titled “clone”

Duplicate the current active branch into a new session at the current position. Can be cancelled by a session_before_fork extension event handler.

{"type": "clone"}

Response:

{
  "type": "response",
  "command": "clone",
  "success": true,
  "data": {"cancelled": false}
}

If an extension cancelled the clone:

{
  "type": "response",
  "command": "clone",
  "success": true,
  "data": {"cancelled": true}
}

get_fork_messages

Section titled “get_fork_messages”

Get user messages available for forking.

{"type": "get_fork_messages"}

Response:

{
  "type": "response",
  "command": "get_fork_messages",
  "success": true,
  "data": {
    "messages": [
      {"entryId": "abc123", "text": "First prompt..."},
      {"entryId": "def456", "text": "Second prompt..."}
    ]
  }
}

get_last_assistant_text

Section titled “get_last_assistant_text”

Get the text content of the last assistant message.

{"type": "get_last_assistant_text"}

Response:

{
  "type": "response",
  "command": "get_last_assistant_text",
  "success": true,
  "data": {"text": "The assistant's response..."}
}

Returns {"text": null} if no assistant messages exist.

set_session_name

Section titled “set_session_name”

Set a display name for the current session. The name appears in session listings and helps identify sessions.

{"type": "set_session_name", "name": "my-feature-work"}

Response:

{
  "type": "response",
  "command": "set_session_name",
  "success": true
}

The current session name is available via get_state in the sessionName field. To set the initial name when starting RPC mode, pass --name <name> or -n <name> to the pi --mode rpc process.

Commands

Section titled “Commands”

get_commands

Section titled “get_commands”

Get available commands (extension commands, prompt templates, and skills). These can be invoked via the prompt command by prefixing with /.

{"type": "get_commands"}

Response:

{
  "type": "response",
  "command": "get_commands",
  "success": true,
  "data": {
    "commands": [
      {"name": "session-name", "description": "Set or clear session name", "source": "extension", "path": "/home/user/.pi/agent/extensions/session.ts"},
      {"name": "fix-tests", "description": "Fix failing tests", "source": "prompt", "location": "project", "path": "/home/user/myproject/.pi/agent/prompts/fix-tests.md"},
      {"name": "skill:brave-search", "description": "Web search via Brave API", "source": "skill", "location": "user", "path": "/home/user/.pi/agent/skills/brave-search/SKILL.md"}
    ]
  }
}

Each command has:

  • name: Command name (invoke with /name)
  • description: Human-readable description (optional for extension commands)
  • source: What kind of command:
    • "extension": Registered via pi.registerCommand() in an extension
    • "prompt": Loaded from a prompt template .md file
    • "skill": Loaded from a skill directory (name is prefixed with skill:)
  • location: Where it was loaded from (optional, not present for extensions):
    • "user": User-level (~/.pi/agent/)
    • "project": Project-level (./.pi/agent/)
    • "path": Explicit path via CLI or settings
  • path: Absolute file path to the command source (optional)

Note: Built-in TUI commands (/settings, /hotkeys, etc.) are not included. They are handled only in interactive mode and would not execute if sent via prompt.

Events

Section titled “Events”

Events are streamed to stdout as JSON lines during agent operation. Events do NOT include an id field (only responses do).

Event Types

Section titled “Event Types”
EventDescription
agent_startAgent begins processing
agent_endAgent completes (includes all generated messages)
turn_startNew turn begins
turn_endTurn completes (includes assistant message and tool results)
message_startMessage begins
message_updateStreaming update (text/thinking/toolcall deltas)
message_endMessage completes
tool_execution_startTool begins execution
tool_execution_updateTool execution progress (streaming output)
tool_execution_endTool completes
queue_updatePending steering/follow-up queue changed
compaction_startCompaction begins
compaction_endCompaction completes
auto_retry_startAuto-retry begins (after transient error)
auto_retry_endAuto-retry completes (success or final failure)
extension_errorExtension threw an error

agent_start

Section titled “agent_start”

Emitted when the agent begins processing a prompt.

{"type": "agent_start"}

agent_end

Section titled “agent_end”

Emitted when the agent completes. Contains all messages generated during this run.

{
  "type": "agent_end",
  "messages": [...]
}

turn_start / turn_end

Section titled “turn_start / turn_end”

A turn consists of one assistant response plus any resulting tool calls and results.

{"type": "turn_start"}
{
  "type": "turn_end",
  "message": {...},
  "toolResults": [...]
}

message_start / message_end

Section titled “message_start / message_end”

Emitted when a message begins and completes. The message field contains an AgentMessage.

{"type": "message_start", "message": {...}}
{"type": "message_end", "message": {...}}

message_update (Streaming)

Section titled “message_update (Streaming)”

Emitted during streaming of assistant messages. Contains both the partial message and a streaming delta event.

{
  "type": "message_update",
  "message": {...},
  "assistantMessageEvent": {
    "type": "text_delta",
    "contentIndex": 0,
    "delta": "Hello ",
    "partial": {...}
  }
}

The assistantMessageEvent field contains one of these delta types:

TypeDescription
startMessage generation started
text_startText content block started
text_deltaText content chunk
text_endText content block ended
thinking_startThinking block started
thinking_deltaThinking content chunk
thinking_endThinking block ended
toolcall_startTool call started
toolcall_deltaTool call arguments chunk
toolcall_endTool call ended (includes full toolCall object)
doneMessage complete (reason: "stop", "length", "toolUse")
errorError occurred (reason: "aborted", "error")

Example streaming a text response:

{"type":"message_update","message":{...},"assistantMessageEvent":{"type":"text_start","contentIndex":0,"partial":{...}}}
{"type":"message_update","message":{...},"assistantMessageEvent":{"type":"text_delta","contentIndex":0,"delta":"Hello","partial":{...}}}
{"type":"message_update","message":{...},"assistantMessageEvent":{"type":"text_delta","contentIndex":0,"delta":" world","partial":{...}}}
{"type":"message_update","message":{...},"assistantMessageEvent":{"type":"text_end","contentIndex":0,"content":"Hello world","partial":{...}}}

tool_execution_start / tool_execution_update / tool_execution_end

Section titled “tool_execution_start / tool_execution_update / tool_execution_end”

Emitted when a tool begins, streams progress, and completes execution.

{
  "type": "tool_execution_start",
  "toolCallId": "call_abc123",
  "toolName": "bash",
  "args": {"command": "ls -la"}
}

During execution, tool_execution_update events stream partial results (e.g., bash output as it arrives):

{
  "type": "tool_execution_update",
  "toolCallId": "call_abc123",
  "toolName": "bash",
  "args": {"command": "ls -la"},
  "partialResult": {
    "content": [{"type": "text", "text": "partial output so far..."}],
    "details": {"truncation": null, "fullOutputPath": null}
  }
}

When complete:

{
  "type": "tool_execution_end",
  "toolCallId": "call_abc123",
  "toolName": "bash",
  "result": {
    "content": [{"type": "text", "text": "total 48\n..."}],
    "details": {...}
  },
  "isError": false
}

Use toolCallId to correlate events. The partialResult in tool_execution_update contains the accumulated output so far (not just the delta), allowing clients to simply replace their display on each update.

queue_update

Section titled “queue_update”

Emitted whenever the pending steering or follow-up queue changes.

{
  "type": "queue_update",
  "steering": ["Focus on error handling"],
  "followUp": ["After that, summarize the result"]
}

compaction_start / compaction_end

Section titled “compaction_start / compaction_end”

Emitted when compaction runs, whether manual or automatic.

{"type": "compaction_start", "reason": "threshold"}

The reason field is "manual", "threshold", or "overflow".

{
  "type": "compaction_end",
  "reason": "threshold",
  "result": {
    "summary": "Summary of conversation...",
    "firstKeptEntryId": "abc123",
    "tokensBefore": 150000,
    "estimatedTokensAfter": 32000,
    "details": {}
  },
  "aborted": false,
  "willRetry": false
}

If reason was "overflow" and compaction succeeds, willRetry is true and the agent will automatically retry the prompt.

If compaction was aborted, result is null and aborted is true.

If compaction failed (e.g., API quota exceeded), result is null, aborted is false, and errorMessage contains the error description.

auto_retry_start / auto_retry_end

Section titled “auto_retry_start / auto_retry_end”

Emitted when automatic retry is triggered after a transient error (overloaded, rate limit, 5xx).

{
  "type": "auto_retry_start",
  "attempt": 1,
  "maxAttempts": 3,
  "delayMs": 2000,
  "errorMessage": "529 {\"type\":\"error\",\"error\":{\"type\":\"overloaded_error\",\"message\":\"Overloaded\"}}"
}
{
  "type": "auto_retry_end",
  "success": true,
  "attempt": 2
}

On final failure (max retries exceeded):

{
  "type": "auto_retry_end",
  "success": false,
  "attempt": 3,
  "finalError": "529 overloaded_error: Overloaded"
}

extension_error

Section titled “extension_error”

Emitted when an extension throws an error.

{
  "type": "extension_error",
  "extensionPath": "/path/to/extension.ts",
  "event": "tool_call",
  "error": "Error message..."
}

Extension UI Protocol

Section titled “Extension UI Protocol”

Extensions can request user interaction via ctx.ui.select(), ctx.ui.confirm(), etc. In RPC mode, these are translated into a request/response sub-protocol on top of the base command/event flow.

There are two categories of extension UI methods:

  • Dialog methods (select, confirm, input, editor): emit an extension_ui_request on stdout and block until the client sends back an extension_ui_response on stdin with the matching id.
  • Fire-and-forget methods (notify, setStatus, setWidget, setTitle, set_editor_text): emit an extension_ui_request on stdout but do not expect a response. The client can display the information or ignore it.

If a dialog method includes a timeout field, the agent-side will auto-resolve with a default value when the timeout expires. The client does not need to track timeouts.

Some ExtensionUIContext methods are not supported or degraded in RPC mode because they require direct TUI access:

  • custom() returns undefined
  • setWorkingMessage(), setWorkingIndicator(), setFooter(), setHeader(), setEditorComponent(), setToolsExpanded() are no-ops
  • getEditorText() returns ""
  • getToolsExpanded() returns false
  • pasteToEditor() delegates to setEditorText() (no paste/collapse handling)
  • getAllThemes() returns []
  • getTheme() returns undefined
  • setTheme() returns { success: false, error: "..." }

Note: ctx.mode is "rpc" and ctx.hasUI is true in RPC mode because the dialog and fire-and-forget methods are functional via the extension UI sub-protocol. Use ctx.mode === "tui" to guard TUI-specific features like custom() that require a real terminal.

Extension UI Requests (stdout)

Section titled “Extension UI Requests (stdout)”

All requests have type: "extension_ui_request", a unique id, and a method field.

select

Section titled “select”

Prompt the user to choose from a list. Dialog methods with a timeout field include the timeout in milliseconds; the agent auto-resolves with undefined if the client doesn’t respond in time.

{
  "type": "extension_ui_request",
  "id": "uuid-1",
  "method": "select",
  "title": "Allow dangerous command?",
  "options": ["Allow", "Block"],
  "timeout": 10000
}

Expected response: extension_ui_response with value (the selected option string) or cancelled: true.

confirm

Section titled “confirm”

Prompt the user for yes/no confirmation.

{
  "type": "extension_ui_request",
  "id": "uuid-2",
  "method": "confirm",
  "title": "Clear session?",
  "message": "All messages will be lost.",
  "timeout": 5000
}

Expected response: extension_ui_response with confirmed: true/false or cancelled: true.

input

Section titled “input”

Prompt the user for free-form text.

{
  "type": "extension_ui_request",
  "id": "uuid-3",
  "method": "input",
  "title": "Enter a value",
  "placeholder": "type something..."
}

Expected response: extension_ui_response with value (the entered text) or cancelled: true.

editor

Section titled “editor”

Open a multi-line text editor with optional prefilled content.

{
  "type": "extension_ui_request",
  "id": "uuid-4",
  "method": "editor",
  "title": "Edit some text",
  "prefill": "Line 1\nLine 2\nLine 3"
}

Expected response: extension_ui_response with value (the edited text) or cancelled: true.

notify

Section titled “notify”

Display a notification. Fire-and-forget, no response expected.

{
  "type": "extension_ui_request",
  "id": "uuid-5",
  "method": "notify",
  "message": "Command blocked by user",
  "notifyType": "warning"
}

The notifyType field is "info", "warning", or "error". Defaults to "info" if omitted.

setStatus

Section titled “setStatus”

Set or clear a status entry in the footer/status bar. Fire-and-forget.

{
  "type": "extension_ui_request",
  "id": "uuid-6",
  "method": "setStatus",
  "statusKey": "my-ext",
  "statusText": "Turn 3 running..."
}

Send statusText: undefined (or omit it) to clear the status entry for that key.

setWidget

Section titled “setWidget”

Set or clear a widget (block of text lines) displayed above or below the editor. Fire-and-forget.

{
  "type": "extension_ui_request",
  "id": "uuid-7",
  "method": "setWidget",
  "widgetKey": "my-ext",
  "widgetLines": ["--- My Widget ---", "Line 1", "Line 2"],
  "widgetPlacement": "aboveEditor"
}

Send widgetLines: undefined (or omit it) to clear the widget. The widgetPlacement field is "aboveEditor" (default) or "belowEditor". Only string arrays are supported in RPC mode; component factories are ignored.

setTitle

Section titled “setTitle”

Set the terminal window/tab title. Fire-and-forget.

{
  "type": "extension_ui_request",
  "id": "uuid-8",
  "method": "setTitle",
  "title": "pi - my project"
}

set_editor_text

Section titled “set_editor_text”

Set the text in the input editor. Fire-and-forget.

{
  "type": "extension_ui_request",
  "id": "uuid-9",
  "method": "set_editor_text",
  "text": "prefilled text for the user"
}

Extension UI Responses (stdin)

Section titled “Extension UI Responses (stdin)”

Responses are sent for dialog methods only (select, confirm, input, editor). The id must match the request.

Value response (select, input, editor)

Section titled “Value response (select, input, editor)”
{"type": "extension_ui_response", "id": "uuid-1", "value": "Allow"}

Confirmation response (confirm)

Section titled “Confirmation response (confirm)”
{"type": "extension_ui_response", "id": "uuid-2", "confirmed": true}

Cancellation response (any dialog)

Section titled “Cancellation response (any dialog)”

Dismiss any dialog method. The extension receives undefined (for select/input/editor) or false (for confirm).

{"type": "extension_ui_response", "id": "uuid-3", "cancelled": true}

Error Handling

Section titled “Error Handling”

Failed commands return a response with success: false:

{
  "type": "response",
  "command": "set_model",
  "success": false,
  "error": "Model not found: invalid/model"
}

Parse errors:

{
  "type": "response",
  "command": "parse",
  "success": false,
  "error": "Failed to parse command: Unexpected token..."
}

Types

Section titled “Types”

Source files:

Model

Section titled “Model”
{
  "id": "claude-sonnet-4-20250514",
  "name": "Claude Sonnet 4",
  "api": "anthropic-messages",
  "provider": "anthropic",
  "baseUrl": "https://api.anthropic.com",
  "reasoning": true,
  "input": ["text", "image"],
  "contextWindow": 200000,
  "maxTokens": 16384,
  "cost": {
    "input": 3.0,
    "output": 15.0,
    "cacheRead": 0.3,
    "cacheWrite": 3.75
  }
}

UserMessage

Section titled “UserMessage”
{
  "role": "user",
  "content": "Hello!",
  "timestamp": 1733234567890,
  "attachments": []
}

The content field can be a string or an array of TextContent/ImageContent blocks.

AssistantMessage

Section titled “AssistantMessage”
{
  "role": "assistant",
  "content": [
    {"type": "text", "text": "Hello! How can I help?"},
    {"type": "thinking", "thinking": "User is greeting me..."},
    {"type": "toolCall", "id": "call_123", "name": "bash", "arguments": {"command": "ls"}}
  ],
  "api": "anthropic-messages",
  "provider": "anthropic",
  "model": "claude-sonnet-4-20250514",
  "usage": {
    "input": 100,
    "output": 50,
    "cacheRead": 0,
    "cacheWrite": 0,
    "cost": {"input": 0.0003, "output": 0.00075, "cacheRead": 0, "cacheWrite": 0, "total": 0.00105}
  },
  "stopReason": "stop",
  "timestamp": 1733234567890
}

Stop reasons: "stop", "length", "toolUse", "error", "aborted"

ToolResultMessage

Section titled “ToolResultMessage”
{
  "role": "toolResult",
  "toolCallId": "call_123",
  "toolName": "bash",
  "content": [{"type": "text", "text": "total 48\ndrwxr-xr-x ..."}],
  "isError": false,
  "timestamp": 1733234567890
}

BashExecutionMessage

Section titled “BashExecutionMessage”

Created by the bash RPC command (not by LLM tool calls):

{
  "role": "bashExecution",
  "command": "ls -la",
  "output": "total 48\ndrwxr-xr-x ...",
  "exitCode": 0,
  "cancelled": false,
  "truncated": false,
  "fullOutputPath": null,
  "timestamp": 1733234567890
}

Attachment

Section titled “Attachment”
{
  "id": "img1",
  "type": "image",
  "fileName": "photo.jpg",
  "mimeType": "image/jpeg",
  "size": 102400,
  "content": "base64-encoded-data...",
  "extractedText": null,
  "preview": null
}

Example: Basic Client (Python)

Section titled “Example: Basic Client (Python)”
import subprocess
import json


proc = subprocess.Popen(
    ["pi", "--mode", "rpc", "--no-session"],
    stdin=subprocess.PIPE,
    stdout=subprocess.PIPE,
    text=True
)


def send(cmd):
    proc.stdin.write(json.dumps(cmd) + "\n")
    proc.stdin.flush()


def read_events():
    for line in proc.stdout:
        yield json.loads(line)


# Send prompt
send({"type": "prompt", "message": "Hello!"})


# Process events
for event in read_events():
    if event.get("type") == "message_update":
        delta = event.get("assistantMessageEvent", {})
        if delta.get("type") == "text_delta":
            print(delta["delta"], end="", flush=True)


    if event.get("type") == "agent_end":
        print()
        break

Example: Interactive Client (Node.js)

Section titled “Example: Interactive Client (Node.js)”

See test/rpc-example.ts for a complete interactive example, or src/modes/rpc/rpc-client.ts for a typed client implementation.

For a complete example of handling the extension UI protocol, see examples/rpc-extension-ui.ts which pairs with the examples/extensions/rpc-demo.ts extension.

const { spawn } = require("child_process");
const { StringDecoder } = require("string_decoder");


const agent = spawn("pi", ["--mode", "rpc", "--no-session"]);


function attachJsonlReader(stream, onLine) {
    const decoder = new StringDecoder("utf8");
    let buffer = "";


    stream.on("data", (chunk) => {
        buffer += typeof chunk === "string" ? chunk : decoder.write(chunk);


        while (true) {
            const newlineIndex = buffer.indexOf("\n");
            if (newlineIndex === -1) break;


            let line = buffer.slice(0, newlineIndex);
            buffer = buffer.slice(newlineIndex + 1);
            if (line.endsWith("\r")) line = line.slice(0, -1);
            onLine(line);
        }
    });


    stream.on("end", () => {
        buffer += decoder.end();
        if (buffer.length > 0) {
            onLine(buffer.endsWith("\r") ? buffer.slice(0, -1) : buffer);
        }
    });
}


attachJsonlReader(agent.stdout, (line) => {
    const event = JSON.parse(line);


    if (event.type === "message_update") {
        const { assistantMessageEvent } = event;
        if (assistantMessageEvent.type === "text_delta") {
            process.stdout.write(assistantMessageEvent.delta);
        }
    }
});


// Send prompt
agent.stdin.write(JSON.stringify({ type: "prompt", message: "Hello" }) + "\n");


// Abort on Ctrl+C
process.on("SIGINT", () => {
    agent.stdin.write(JSON.stringify({ type: "abort" }) + "\n");
});