> ## Documentation Index > Fetch the complete documentation index at: https://hastekit.ai/docs/llms.txt > Use this file to discover all available pages before exploring further. # Chat > Test your agent in a built-in chat UI — no separate client required The Chat tab is the fastest path from "I saved this agent" to "I'm watching it answer." It supports every feature of the runtime — multi-turn history, tool calls, structured output, attachments, voice — in a UI you can use without writing any client code. Conversational UI for Agents ## Layout * **Sidebar** — past conversations grouped under "Chats." Click any one to resume; click **New Chat** to start fresh. * **Main chat area** — message history with inline rendering of tool calls (each shows its name, arguments, and result). * **Input bar** — the agent picker, version picker, context dialog, attachment buttons, and message input. ## Picking an agent and version * Click the **agent name** button above the input field to switch agents. * Click the **version** button (defaults to `Latest`) to pin the chat to a specific version. Version 0 (`$LATEST`) is always the current mutable working copy; numbered versions are immutable snapshots. See [Versioning](/docs/gateway/agent-builder/versioning). * Picking an [alias](/docs/gateway/agent-builder/alias) (e.g. `production`) routes each turn to whichever version the alias currently points at. ## Adding context Click the **@** button to open the **Add Context** dialog: * **Context** — a JSON object passed alongside each message. Useful for templated [system prompts](/docs/gateway/agent-builder/system-prompt) (`{{user_name}}`, `{{org_id}}`, …) or anything else your agent reads from the request body. * **Headers** — a JSON object of HTTP headers added to each request — auth tokens, user IDs, anything you'd want a real client to send. Both values persist for the rest of the conversation. ## Attachments * **Files** — paperclip icon. Attach PDFs, images, and other files inline with a message. The agent's model needs to support the file type natively (e.g. vision for images, document inputs for PDFs). * **Audio** — microphone icon. Record voice input directly. Useful for testing agents wired to the [Transcript Generation tool](/docs/gateway/agent-builder/provider-tools). ## Tool-call visualization Every tool call the agent makes shows up inline in the chat as a labeled block: * Tool name and source (e.g. `Google Calendar: List Events`, `MCP: search_repo`). * Arguments the agent sent. * The tool's result. Click any block to jump to its span in the full [trace](/docs/gateway/agent-builder/traces). ## Sending messages Type into **Ask anything** and press Enter (or click send). The response **streams** in token-by-token. Tool calls execute inline and stream their results as they complete. ## Useful per-message actions Each assistant message has a footer row: * **Copy** the response. * **Thumbs up / thumbs down** for feedback (logged for evals). * **Regenerate** to re-run the last turn. * **View trace** to jump straight to the OpenTelemetry trace for the run. ## When to use Chat vs the HTTP API | Use Chat for | Use the HTTP API for | | ------------------------------- | ------------------------------------------------------------------------------------------------------------------- | | Manual testing during iteration | Production traffic | | Debugging tool calls visually | Integration with your app | | Demoing the agent to others | Driving the agent from a [workflow](/docs/gateway/agent-builder/workflows) or [channel](/docs/gateway/agent-builder/channels) |