# Per-tool policy bindings

> Field reference for per-tool OPA policy bindings on an MCP Proxy hop, configured from the Managed Agent's via MCP Proxy endpoint rather than a standalone canvas element.

Per-tool policy bindings attach an OPA policy to an individual MCP tool name, so one tool’s tools/call requests can be evaluated against a different Rego rule than another’s. This is not a draggable canvas element. Select a Managed Agent node on an MCP surface, set Endpoint Type to via MCP Proxy, then select the node labelled MCP Proxy in the synthesised chain the canvas adds between the Managed Agent and the proxy.

- Leave Default Tool Policy unset and add no per-tool rules to leave every tool callable with no gating.

- Set a Default Tool Policy to evaluate every tool that has no rule of its own against that one policy, instead of allowing it unconditionally.

- Add a per-tool rule only for the tools that need a policy different from the default.

## Fields

Each row in the tool entry list configures one tool. Default Tool Policy sits above the list and applies to every tool the list does not cover.

| Field | What it does | Default |
| Tool name | Name of the MCP tool this rule applies to. Must match the tool name exactly as defined in the MCP server or proxy. | — |
| Policy Definition | The policy definition this tool is evaluated against at tools/call time, selected from your existing OPA policy definitions. Uses the McpPolicyContext input schema. | — |
| Description | A note shown in the dashboard. Has no runtime effect. | — |
| Default Tool Policy | The policy definition evaluated for any tool the entry list does not cover. | None: an uncovered tool is allowed |

This element is distinct from MCP Tool Gating, a separate Agent Surface canvas element that filters tools by regex pattern rather than OPA policy per exact name.

## The “MCP Tools” node is a different, read-only view

The synthesised chain for a via MCP Proxy endpoint is MCP Proxy → REST API → MCP Tools. The last node in that chain is visually labelled MCP Tools, but it is unrelated to the per-tool policy bindings on this page: selecting it opens a read-only, filterable Exposed Tools list, live-fetched from the proxy, with no policy fields. If you are looking for the fields on this page, select the node labelled MCP Proxy instead.

## Related

- [Control MCP tool access with per-tool policies](/products/affinidi-trust-fabric/agent-gateway/how-to-guides/policies/control-mcp-tool-access-with-per-tool-policies.md): step-by-step guide to configuring tool policies on an MCP Proxy hop.

- [OPA policies reference](/products/affinidi-trust-fabric/agent-gateway/reference/surfaces/opa-policies.md#mcp-tool-policy-input): the McpPolicyContext input schema used when a tool policy evaluates.

- [Managed Agent reference](/products/affinidi-trust-fabric/agent-gateway/reference/surfaces/managed-agent.md): the via MCP Proxy endpoint type that surfaces this panel.