diff --git a/README.md b/README.md
index ef454e0..21cfdba 100644
--- a/README.md
+++ b/README.md
@@ -77,14 +77,14 @@ prompted to keep yours, take the remote's, or rename the remote entry.
 
 ## What's in this template
 
-| Asset  | File                              | What it is                                              |
-|--------|-----------------------------------|---------------------------------------------------------|
-| Agent  | `agents/hello-agent/config.yaml`  | Tiny LLM-loop agent that greets the user.               |
-| Role   | `roles/explainer.md`              | Role that explains technical concepts simply.           |
-| Skill  | `skills/rust-fmt/SKILL.md`        | Skill demonstrating `enabled_tools` + `auto_unload`.    |
-| Macro  | `macros/greet.yaml`               | Macro showing positional and rest-arg variables.        |
-| Tool   | `functions/tools/greet.sh`        | Bash tool using Coyote's argc-style annotations.          |
-| MCP    | `functions/mcp.json`              | One vanilla server + one with a vault secret reference. |
+| Asset | File                             | What it is                                              |
+|-------|----------------------------------|---------------------------------------------------------|
+| Agent | `agents/hello-agent/config.yaml` | Tiny LLM-loop agent that greets the user.               |
+| Role  | `roles/explainer.md`             | Role that explains technical concepts simply.           |
+| Skill | `skills/rust-fmt/SKILL.md`       | Skill demonstrating `enabled_tools` + `auto_unload`.    |
+| Macro | `macros/greet.yaml`              | Macro showing positional and rest-arg variables.        |
+| Tool  | `functions/tools/greet.sh`       | Bash tool using Coyote's argc-style annotations.        |
+| MCP   | `functions/mcp.json`             | One vanilla server + one with a vault secret reference. |
 
 Each sample is intentionally minimal. Replace it with your own work, or
 delete what you don't need.
@@ -128,6 +128,31 @@ Use `{{SECRET_NAME}}` placeholders for values you don't want to commit;
 Coyote will detect missing secrets after the merge and prompt you to add
 them to the vault (or list them for you to add via `coyote --add-secret`).
 
+### (Optional) Sandbox mixins (`sbx-mixin.yaml`)
+If consumers of your bundle run Coyote in [Sandbox mode](https://github.com/Dark-Alex-17/coyote/wiki/Sandboxes),
+they'll need any external binaries and network domain allowances declared
+in an `sbx-mixin.yaml` file. Coyote auto-discovers mixin files at known
+locations on every `coyote --sandbox` invocation, no flags required.
+
+This template ships two starter examples:
+
+- **`agents/hello-agent/sbx-mixin.yaml`:** Per-agent mixin, applied when
+  the agent is installed and any `coyote --sandbox` runs.
+- **`functions/sbx-mixin.yaml`:** Shared by all custom tools in this
+  bundle. For per-tool granularity, use `functions/<tool>/sbx-mixin.yaml`
+  instead.
+
+Both starters are commented-out templates. Simply open them and fill in the
+domains and install commands your assets actually need. Delete the files
+if they're not needed.
+
+> ⚠️ **Privilege grant.** Anyone installing your bundle is granting the
+> mixins' install commands (passwordless sudo) and network domain
+> allowances inside their sandboxes. Document any non-obvious entries in
+> this README so they don't have to grep your YAML to find out what
+> they're accepting. See the [Sharing Configurations - Sandbox Implications](https://github.com/Dark-Alex-17/coyote/wiki/Sharing-Configurations#sandbox-implications)
+> wiki page for the full security model.
+
 ## Secrets workflow
 
 Anywhere you reference a secret in `mcp.json` (or in any installed file),
diff --git a/agents/hello-agent/sbx-mixin.yaml b/agents/hello-agent/sbx-mixin.yaml
new file mode 100644
index 0000000..c995329
--- /dev/null
+++ b/agents/hello-agent/sbx-mixin.yaml
@@ -0,0 +1,23 @@
+schemaVersion: "1"
+kind: mixin
+name: agent-hello
+description: >
+  Example sbx mixin for the hello-agent. Coyote auto-discovers and applies
+  any sbx-mixin.yaml co-located with an agent whenever you run
+  `coyote --sandbox`. Use this to declare any binaries the agent needs to
+  install inside the sandbox and any network domains it needs to reach.
+  Delete this file if your agent doesn't need extra sandbox setup.
+
+network:
+  allowedDomains:
+    # Replace with the domains your agent actually hits.
+    # Example: an agent that calls api.example.com would add:
+    # - "api.example.com:443"
+
+commands:
+  install:
+    # Replace with any binaries your agent depends on. Runs as the
+    # `agent` user (UID 1000) with passwordless sudo. Example:
+    # - command: "sudo apt-get update && sudo apt-get install -y httpie"
+    #   user: "1000"
+    #   description: Install httpie for hello-agent's API calls
diff --git a/functions/sbx-mixin.yaml b/functions/sbx-mixin.yaml
new file mode 100644
index 0000000..00476e3
--- /dev/null
+++ b/functions/sbx-mixin.yaml
@@ -0,0 +1,25 @@
+schemaVersion: "1"
+kind: mixin
+name: shared-custom-tools
+description: >
+  Example global sbx mixin that applies to every Coyote sandbox you launch.
+  Use this for binaries and network domains shared by multiple custom tools
+  in functions/tools/. For per-tool needs that aren't shared, create
+  functions/<tool-name>/sbx-mixin.yaml instead (per-tool mixins are also
+  auto-discovered).
+
+  Delete this file if your fork doesn't need extra sandbox setup.
+
+network:
+  allowedDomains:
+    # Replace with the domains your custom tools reach.
+    # Example: a tool that calls a private API:
+    # - "api.your-company.com:443"
+
+commands:
+  install:
+    # Replace with binaries your custom tools depend on. Runs as the
+    # `agent` user (UID 1000) with passwordless sudo. Example:
+    # - command: "sudo apt-get update && sudo apt-get install -y httpie xmlstarlet"
+    #   user: "1000"
+    #   description: Install custom tool dependencies