--- title: OpenCode description: Learn how to use the OpenCode harness adapter. url: "https://ai-sdk.dev/providers/ai-sdk-harnesses/opencode" docs_index: /llms.txt --- > For an index of all documentation, see [/llms.txt](/llms.txt). The OpenCode harness adapter connects `HarnessAgent` to OpenCode through `@opencode-ai/sdk`. The adapter runs a bridge inside the sandbox, starts an OpenCode server in that sandbox, and streams OpenCode session events back to the host over a sandbox-exposed WebSocket. Harness packages are **experimental**. Expect breaking changes between releases as this early API gets further refined. ## Setup ```bash pnpm add @ai-sdk/harness @ai-sdk/harness-opencode @ai-sdk/sandbox-vercel ``` The adapter bootstraps the OpenCode bridge dependencies inside the sandbox when the first session starts. The bridge package depends on `@opencode-ai/sdk` and `opencode-ai`. ## Import ```ts import { openCode, createOpenCode } from '@ai-sdk/harness-opencode'; ``` `openCode` is equivalent to `createOpenCode()` with its default configuration. ## Basic Usage ```ts import { HarnessAgent } from '@ai-sdk/harness/agent'; import { openCode } from '@ai-sdk/harness-opencode'; import { createVercelNetworkSandboxSession } from '@ai-sdk/sandbox-vercel'; const agent = new HarnessAgent({ harness: openCode, model: 'anthropic/claude-sonnet-4-6', }); const sandboxSession = await createVercelNetworkSandboxSession({ runtime: 'node24', ports: [4000], template: await agent.getSandboxTemplate(), }); const session = await agent.createSession({ sandboxSession }); let exitCode = 0; try { const result = await agent.stream({ session, prompt: 'Check the test failures and fix the production code.', }); for await (const part of result.stream) { if (part.type === 'text-delta') { process.stdout.write(part.text); } } } catch (err) { exitCode = 1; console.error(err); } finally { await session.destroy(); await sandboxSession.destroy(); process.exit(exitCode); } ``` To use this agent, ensure environment variables include `VERCEL_OIDC_TOKEN` for Vercel Sandbox, and one of the variables listed under [authentication](#authentication) for OpenCode. ## Adapter Settings Use `createOpenCode()` to configure the runtime: ```ts const harness = createOpenCode({ reasoningVariant: 'high', openCodeConfig: { agent: { general: { model: 'openai/gpt-5.4-mini', }, }, }, }); ``` Settings: - `auth`: authentication mode (`auto`, `direct`, `anthropic`, `openai`, or `ai-gateway`) or an isolated authentication environment. - `credentialForwarding`: optional synchronous or asynchronous callback that customizes each credential immediately before the harness adapter forwards it into a sandbox process. It receives the credential value that would otherwise be forwarded (either the real credential or a masked value) and the environment variable name used to expose it. This callback only controls the value forwarded into the sandbox process. It does not restrict which credentials the harness adapter can discover, read, or otherwise access in the host process. - `mcpServers`: MCP server definitions keyed by server name. - `openCodeConfig`: additional native OpenCode configuration. Adapter-managed settings take precedence. Agent-local `permission` and deprecated `tools` settings are ignored so they cannot bypass harness permissions or built-in tool filtering. - `provider`: provider id to use when `model` on `HarnessAgent` is unprefixed. - `reasoningVariant`: OpenCode reasoning/thinking variant for supported models, such as `low`, `medium`, or `high`. - `port`: bridge port override. - `startupTimeoutMs`: maximum time to wait for the bridge to start. - `hostDisconnectTimeoutMs`: aborts a running turn when the host disconnects and no host reconnects within this many milliseconds. A suspended turn is not aborted. When unset, a turn keeps running in the sandbox after its host disconnects, including when the host process is gone for good, until the turn finishes or the sandbox stops. - `reconnect`: reconnect timing after an established bridge WebSocket connection drops. `maxElapsedMs` controls the total retry window, including connection establishment and backoff delays, and defaults to 30 seconds. `initialDelayMs` defaults to 50 milliseconds, and `maxDelayMs` defaults to 2 seconds. These retries use exponential backoff and are separate from `startupTimeoutMs`. They cannot recover when the sandbox, bridge process, or bridge endpoint is permanently unavailable. - `mintBridgeToken`: synchronous function that receives the sandbox id and returns the bridge authentication token. By default, the adapter generates a random 32-byte token. Custom implementations must return a suitably secret token. ## Structured Output OpenCode supports schema-backed [`HarnessAgent` structured output](/docs/ai-sdk-harnesses/harness-agent#generate-structured-output). The adapter uses OpenCode's `json_schema` prompt format and returns the validated `structured` result as JSON text. ## Authentication The `auth` setting selects how credentials are resolved from the host environment: - `auto` (default): use AI Gateway credentials when available, then use the credentials for the selected model provider. - `direct`: use the credentials for the selected model provider. - `anthropic`: use Anthropic credentials. - `openai`: use OpenAI credentials. - `ai-gateway`: use AI Gateway credentials. When the sandbox supports additive request transformations, the bridge receives placeholders and the adapter injects credentials into matching outbound requests. Sandboxes without that capability retain direct credential forwarding. Supported environment variables: - `AI_GATEWAY_API_KEY` - `AI_GATEWAY_BASE_URL` - `VERCEL_OIDC_TOKEN` - `ANTHROPIC_API_KEY` - `ANTHROPIC_AUTH_TOKEN` - `ANTHROPIC_BASE_URL` - `OPENAI_API_KEY` - `OPENAI_BASE_URL` - `OPENAI_ORGANIZATION` - `OPENAI_PROJECT` If no applicable credential environment variable is set, the adapter attempts to resolve a native subscription from the host system unless AI Gateway authentication is selected. Select a specific authentication mode when you do not want automatic detection: ```ts const directHarness = createOpenCode({ auth: 'direct' }); const anthropicHarness = createOpenCode({ auth: 'anthropic' }); const openAIHarness = createOpenCode({ auth: 'openai' }); const gatewayHarness = createOpenCode({ auth: 'ai-gateway' }); ``` Pass an authentication environment to use programmatically resolved credentials without reading `process.env`: ```ts const harness = createOpenCode({ auth: { OPENAI_API_KEY: await resolveOpenAIToken() }, provider: 'openai', }); ``` The supplied record replaces the host environment for authentication discovery. Only recognized authentication variables are forwarded. For OpenAI-compatible endpoints, select `openai` and set `OPENAI_BASE_URL`. ## Sandbox OpenCode requires a network sandbox with at least one exposed port, e.g. `@ai-sdk/sandbox-vercel`: ```ts const sandboxSession = await createVercelNetworkSandboxSession({ runtime: 'node24', ports: [4000], template: await agent.getSandboxTemplate(), }); ``` ## Built-in Tools The adapter exposes these common OpenCode built-ins through `agent.tools`: - `read` - `write` - `edit` - `bash` - `glob` - `grep` - `ls` - `webfetch` - `skill` - `todowrite` - `agent` Additional OpenCode built-ins may also appear in `agent.tools` when they do not fit a common tool shape. OpenCode supports built-in tool approval requests when `permissionMode` is `allow-reads` or `allow-edits`. Host-executed AI SDK tool approvals also work. In these modes, file reads are automatically approved only within the session workdir or an active skill's directory. `allow-edits` automatically approves file changes only within the workdir. Paths outside those directories, including symlink targets, and paths that cannot be resolved require host approval. Approvals apply only to the current tool call, not subsequent calls. `allow-all` remains unrestricted. These approval rules are not a filesystem sandbox, and approved shell commands can access paths outside the workdir. ## Built-in Tool Filtering The adapter supports `activeTools` and `inactiveTools` for OpenCode built-in tools. It uses OpenCode's native `permission: 'deny'` rules, which keep inactive built-ins out of the model-facing tool list. OpenCode groups its native `write` and `edit` tools under the same `edit` permission. Keep the Harness `write` and `edit` tools in the same active or inactive state. Filtering only one of them causes session startup to throw a `HarnessCapabilityUnsupportedError`. ## Related - [HarnessAgent](/docs/ai-sdk-harnesses/harness-agent) - [Harness tools](/docs/ai-sdk-harnesses/tools) - [Harness adapters](/docs/ai-sdk-harnesses/harness-adapters) --- For a semantic overview of all documentation, see [/sitemap.md](/sitemap.md) For an index of all available documentation, see [/llms.txt](/llms.txt) For agent-facing discovery, including API and MCP surfaces, see [/agents.md](/agents.md)