Protocol Types

ACP protocol type definitions and enumerations

Overview

The ACP::Protocol module contains all JSON-RPC 2.0 and ACP schema types. All types use JSON::Serializable and many use discriminated unions for polymorphic deserialization.

Enumerations

StopReason

enum ACP::Protocol::StopReason
  EndTurn
  MaxTokens
  MaxTurnRequests
  Refusal
  Cancelled
end

ToolKind

enum ACP::Protocol::ToolKind
  Read
  Edit
  Delete
  Move
  Search
  Execute
  Think
  Fetch
  SwitchMode
  Other
end

ToolCallStatus

enum ACP::Protocol::ToolCallStatus
  Pending
  InProgress
  Completed
  Failed
end

PermissionOptionKind

enum ACP::Protocol::PermissionOptionKind
  AllowOnce
  AllowAlways
  RejectOnce
  RejectAlways
end

PlanEntryPriority

enum ACP::Protocol::PlanEntryPriority
  High
  Medium
  Low
end

PlanEntryStatus

enum ACP::Protocol::PlanEntryStatus
  Pending
  InProgress
  Completed
end

SessionConfigOptionCategory

enum ACP::Protocol::SessionConfigOptionCategory
  Mode
  Model
  ThoughtLevel
  Other
end

Role

enum ACP::Protocol::Role
  Assistant
  User
end

Content Blocks

Content blocks are used to construct prompts. They form a discriminated union (ContentBlock):

Type	Description
`TextContentBlock`	Plain text with optional annotations
`ImageContentBlock`	Base64 image with MIME type
`AudioContentBlock`	Base64 audio with MIME type
`ResourceContentBlock`	Embedded resource (URI + content)
`ResourceLinkContentBlock`	Resource link with metadata
`FileContentBlock`	Backward-compatible alias for `ResourceLinkContentBlock`

Tool Call Content

Types for tool call content within updates:

Type	Description
`ToolCallContentBlock`	Wraps a standard content block
`ToolCallDiff`	File modification diff (path, oldText, newText)
`ToolCallTerminal`	Embedded terminal reference by ID
`ToolCallLocation`	File location tracking (path, line)

Session Update Types

Session updates are received via the on_update callback. They form a discriminated union (SessionUpdate):

Type	Key Fields
`AgentMessageChunkUpdate`	`delta : String`
`AgentThoughtChunkUpdate`	`delta : String`
`ToolCallUpdate`	`tool_name : String`, `tool_call_id : String`
`ToolCallStatusUpdate`	`status : ToolCallStatus`, `tool_call_id : String`
`PlanUpdate`	`entries : Array(PlanEntry)`
`UserMessageChunkUpdate`	`delta : String`
`AvailableCommandsUpdate`	`commands : Array(Command)`
`CurrentModeUpdate`	`mode_id : String`
`ConfigOptionUpdate`	`config_id : String`, `value : JSON::Any`

Capabilities

ClientCapabilities

ACP::Protocol::ClientCapabilities.new(
  fs : FsCapabilities? = nil,
  terminal : Bool? = nil
)

Field	Type	Description
`fs`	`FsCapabilities?`	File system capabilities
`terminal`	`Bool?`	Terminal support

FsCapabilities

ACP::Protocol::FsCapabilities.new(
  read_text_file : Bool? = nil,
  write_text_file : Bool? = nil
)

AgentCapabilities

Field	Type	Description
`load_session`	`Bool?`	Session loading support
`prompt_capabilities`	`PromptCapabilities?`	Prompt format support
`mcp_capabilities`	`McpCapabilities?`	MCP support
`session_capabilities`	`SessionCapabilities?`	Session features

PromptCapabilities

Field	Type	Description
`image`	`Bool?`	Image content support
`audio`	`Bool?`	Audio content support
`embedded_context`	`Bool?`	Embedded context support

Client Methods

Types for agent-initiated requests:

File System

Method	Params	Result
`fs/read_text_file`	`ReadTextFileParams`	`ReadTextFileResult`
`fs/write_text_file`	`WriteTextFileParams`	`WriteTextFileResult`

Terminal

Method	Params	Result
`terminal/create`	`CreateTerminalParams`	`CreateTerminalResult`
`terminal/output`	`TerminalOutputParams`	`TerminalOutputResult`
`terminal/release`	`ReleaseTerminalParams`	`ReleaseTerminalResult`
`terminal/wait_for_exit`	`WaitForTerminalExitParams`	`WaitForTerminalExitResult`
`terminal/kill`	`KillTerminalParams`	`KillTerminalResult`

Error Codes

module ACP::Protocol::ErrorCode
  PARSE_ERROR       = -32700
  INVALID_REQUEST   = -32600
  METHOD_NOT_FOUND  = -32601
  INVALID_PARAMS    = -32602
  INTERNAL_ERROR    = -32603
  AUTH_REQUIRED     = -32000
  RESOURCE_NOT_FOUND = -32002
end