# Glossary (/docs/reference/glossary)



**A2A (Agent2Agent).** An open protocol for agents to discover each other and exchange tasks over HTTP. See [What is A2A?](/docs/concepts/a2a-protocol).

**Agent card.** JSON at `/.well-known/agent-card.json` describing an agent's name, skills and endpoints. See [agent cards](/docs/concepts/agent-cards).

**Artifact.** An output of a task, delivered as parts. The final answer is normally an artifact.

**Backend.** The agent product a wrapper exposes: Copilot, Claude, Codex, OpenCode or Antigravity.

**BYOK (bring your own key/model).** Pointing `a2a-copilot` at your own provider, such as Ollama, OpenAI, Anthropic or Azure, instead of GitHub Copilot's hosted models.

**Canary.** An unreviewed npm release published after every merge to `main`. Installed with `@canary`.

**Context / contextId.** An identifier grouping related messages into one conversation. Wrappers map it to a backend session. See [sessions](/docs/concepts/sessions).

**Core (`@a2a-wrapper/core`).** The shared package holding all protocol, server, config, session and event logic.

**Executor.** The backend-specific class a wrapper implements (`A2AExecutor`) to run tasks.

**JSON-RPC.** The message format for A2A's primary transport. The endpoint is `/a2a/jsonrpc`.

**MCP (Model Context Protocol).** An open protocol for connecting agents to tools and data. A2A is its horizontal counterpart. See [MCP tool servers](/docs/guides/mcp-tools).

**Message.** One turn of communication, made of parts, with a `user` or `agent` role.

**Orchestrator.** A client or framework that discovers agents and delegates work to them.

**Permission mode / sandbox mode.** Controls on what a backend may do in the workspace, for example `permissionMode` in `a2a-claude` and `sandboxMode` in `a2a-codex`. See the [security guide](/docs/guides/security).

**Sideband event.** An observability event (tool call, reasoning, file change, usage) emitted alongside the answer. See [observability](/docs/concepts/observability).

**Skill (agent card).** A capability advertised to callers for discovery and routing.

**Skill (memory).** A `SKILL.md` folder of instructions written into the workspace for the model. See [memory and skills](/docs/concepts/memory-and-skills).

**Sub-agent.** A remote A2A agent a wrapper exposes to its model as tools. See [sub-agents](/docs/concepts/sub-agents).

**Task.** A unit of work with a lifecycle: `submitted`, `working`, `input-required`, `completed`, `failed` or `canceled`.

**Workspace.** The directory a wrapper's agent may read and modify, set with `WORKSPACE_DIR`.