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VS Code Extension

The A2A Editor for VS Code brings the full A2A playground experience into your IDE. Browse, edit, validate, and chat with A2A agents without leaving VS Code.

Features​

  • Activity Bar Sidebar — Dedicated A2A icon with auto-detection of agent card files in the active editor
  • Custom Editor — Open *.agentcard.json, agent-card.json, or agent.json files as rendered, interactive agent cards
  • Agent Overview — View agent name, version, provider, description, capabilities, skills, and security schemes at a glance
  • Chat & Testing — Send messages to connected A2A agents and inspect raw HTTP request/response payloads
  • URL Discovery — Connect to agents via URL with automatic well-known path resolution
  • Authentication — Built-in support for Basic Auth, Bearer Token, and API Key authentication
  • Theme Integration — Follows VS Code light, dark, and high-contrast themes

Installation​

From source​

git clone https://github.com/open-resource-discovery/a2a-editor-vscode.git
cd a2a-editor-vscode
npm install
npm run package

Then install the produced .vsix:

code --install-extension a2a-editor-vscode-<version>.vsix

Or via the UI: Extensions view → … menu → Install from VSIX….

Usage​

Click the A2A icon in the Activity Bar to open the sidebar. It automatically detects when the active editor contains an agent card JSON file. Enter a URL to connect to a remote agent, or toggle between URL and file sources.

Custom Editor​

Open any agent card JSON file, then run the command palette (Cmd+Shift+P / Ctrl+Shift+P) → "A2A: Open Current File as Agent Card" to open it as a visual card. Edits sync bidirectionally between the visual editor and the underlying JSON file.

Supported file patterns​

The custom editor activates as an alternative (non-default) editor for:

  • *.agentcard.json
  • agent-card.json
  • agent.json

URL Discovery & Authentication​

When connecting by URL the extension tries these paths in order:

  1. <url>/.well-known/agent.json
  2. <url>/.well-known/agent-card.json
  3. The original URL directly

If the URL ends in .json it is fetched directly without well-known discovery.

Supported authentication methods: No Auth, Basic Auth, Bearer Token, API Key.

MCP Server​

The extension ships an in-process MCP (Model Context Protocol) server so AI tools like GitHub Copilot, Claude Code, Cursor, or Cline can drive A2A agents through the same code paths as the editor. It starts automatically when VS Code loads the extension.

Exposed tools​

ToolPurpose
a2aAgentCard_fetchAgentCardFetch an agent card from a URL
a2aAgentCard_validateAgentCardValidate an agent card JSON string against the A2A schema
a2aAgentCard_sendMessageSend a test message to an agent via A2A JSON-RPC

Client setup​

ClientSetup
GitHub CopilotAuto-discovered via VS Code 1.110+ — no extra config needed
Claude CodeRun claude mcp add --transport http a2a-editor http://127.0.0.1:39627/mcp, then verify with /mcp
Cursor / ClineAdd {"mcpServers": {"a2a-editor": {"url": "http://127.0.0.1:39627/mcp"}}} to your MCP config

The server binds to http://127.0.0.1:39627/mcp by default. Configure via VS Code settings: a2aAgentCard.mcp.enabled, a2aAgentCard.mcp.host, a2aAgentCard.mcp.port.

note

The VS Code window running the extension must be open for the MCP server to be reachable.

Requirements​

  • VS Code >= 1.110
  • Node.js >= 24 (for building from source)