AgentGuards plugin for OpenCode

LLM security guardrails for OpenCode: jailbreak and prompt-injection detection, web-content scanning, and destructive-command authorization — enforced in-process, before the model ever sees a flagged prompt or fetched page.

Enforcement is configurable: fail-closed by default for strict security, or switch to fail-open (availability-first) with a single environment variable (AGENTGUARDS_FAIL_OPEN=true).

This plugin bundles:

• enforcing hooks — chat.message prompt scanning, bash command authorization (a borderline command is blocked with a reason — re-run once you've confirmed you want to proceed), and post-execution web-content scanning/redaction for webfetch and curl/wget-style bash calls,
• the AgentGuards security instructions (the guardrails skill), for cooperative use of the AgentGuards MCP tools.

The AgentGuards MCP server (check_input, authorize_action, validate_output, evaluate_policy, health_check) is set up separately — see MCP setup below — since OpenCode's plugin API and its MCP registration are independent mechanisms (unlike Claude Code, which bundles both from one plugin install).

Install the plugin

npm (recommended):

opencode plugin @agentguardsco/opencode-plugin

Add -g/--global to install for all projects instead of just the current one.

Local file (no npm): copy plugin/agentguards-opencode-plugin.ts to .opencode/plugin/ in your project (or your global OpenCode config directory) — OpenCode auto-loads any plugin file it finds there.

Set your API key

export AGENTGUARDS_API_KEY=ag_your_token_here

Get a key at https://agentguards.co/dashboard/keys. Add that line to your shell profile (~/.bashrc, ~/.zshrc, …) and restart OpenCode.

Set up the MCP server (optional, for cooperative checks)

opencode mcp add agentguards \
  --url https://prod.agentguards.co/mcp \
  --header 'X-API-Key=${AGENTGUARDS_API_KEY}'

Quote the header value with single quotes so your shell doesn't expand ${AGENTGUARDS_API_KEY} before OpenCode sees it — OpenCode resolves the placeholder itself from your environment at connect time, so the raw key is never written to your opencode.json/opencode.jsonc. Verify with opencode mcp list.

Configuration

Variable	Required	Default	Purpose
AGENTGUARDS_API_KEY	yes	—	Your ag_ token. Drives both the hooks and the MCP header.
AGENTGUARDS_URL	no	https://prod.agentguards.co	Override only for a self-hosted instance.
AGENTGUARDS_FAIL_OPEN	no	false	Hooks fail closed by default (block when the service is unreachable). Set true to allow on error.

How it works

The plugin calls the AgentGuards REST API on every chat message, before every bash command, and after every web fetch — blocking or redacting when AgentGuards flags a risk. A borderline bash command (e.g. one AgentGuards scores as require-approval) is blocked with a message telling you to re-run it once you've confirmed you want to proceed, rather than being silently allowed. The MCP tools let the model cooperatively check inputs and authorize actions as described in the bundled guardrails skill.

Learn more at https://agentguards.co.