diff --git a/MCP-Servers.md b/MCP-Servers.md
index 24f8519..cee0df2 100644
--- a/MCP-Servers.md
+++ b/MCP-Servers.md
@@ -93,12 +93,13 @@ For remote MCP servers that support the Streamable HTTP transport:
 }
 ```
 
-| Field             | Required | Description                                                                                    |
-|-------------------|----------|------------------------------------------------------------------------------------------------|
-| `type`            | yes      | Must be `"http"`                                                                               |
-| `url`             | yes      | The server endpoint URL                                                                        |
-| `headers`         | no       | Custom HTTP headers to include with every request                                              |
-| `oauth_client_id` | no       | OAuth client ID. Omit to use Dynamic Client Registration (auto-registers on first `.mcp auth`) |
+| Field                | Required | Description                                                                                                   |
+|----------------------|----------|---------------------------------------------------------------------------------------------------------------|
+| `type`               | yes      | Must be `"http"`                                                                                              |
+| `url`                | yes      | The server endpoint URL                                                                                       |
+| `headers`            | no       | Custom HTTP headers to include with every request                                                             |
+| `oauth.clientId`     | no       | OAuth client ID. Omit to use Dynamic Client Registration (auto-registers on first `.mcp auth`)                |
+| `oauth.callbackPort` | no       | Callback port for the OAuth redirect listener. Required when the server enforces a specific redirect URI port |
 
 ## SSE Servers
 
@@ -119,12 +120,13 @@ prefer `http` where the server supports it):
 }
 ```
 
-| Field             | Required | Description                                                                                    |
-|-------------------|----------|------------------------------------------------------------------------------------------------|
-| `type`            | yes      | Must be `"sse"`                                                                                |
-| `url`             | yes      | The server SSE endpoint URL                                                                    |
-| `headers`         | no       | Custom HTTP headers to include with every request                                              |
-| `oauth_client_id` | no       | OAuth client ID. Omit to use Dynamic Client Registration (auto-registers on first `.mcp auth`) |
+| Field                | Required | Description                                                                                                   |
+|----------------------|----------|---------------------------------------------------------------------------------------------------------------|
+| `type`               | yes      | Must be `"sse"`                                                                                               |
+| `url`                | yes      | The server SSE endpoint URL                                                                                   |
+| `headers`            | no       | Custom HTTP headers to include with every request                                                             |
+| `oauth.clientId`     | no       | OAuth client ID. Omit to use Dynamic Client Registration (auto-registers on first `.mcp auth`)                |
+| `oauth.callbackPort` | no       | Callback port for the OAuth redirect listener. Required when the server enforces a specific redirect URI port |
 
 **Note:** Both `http` and `sse` types use the same underlying transport, which auto-negotiates the
 protocol with the server. The `type` field primarily serves as documentation of which protocol the
@@ -170,7 +172,8 @@ automatically. When the token expires it is refreshed silently.
 2. **Dynamic Client Registration (RFC 7591):** If the server supports it (the Notion MCP server used in this example does), Coyote
    registers itself automatically and caches the client ID in `~/.cache/coyote/oauth/mcp_<name>_registration.json`. The
    `oauth_client_id` field is only needed when DCR is unavailable.
-3. **PKCE authorization code flow:** A localhost callback server is bound on an ephemeral port. Your browser opens for login.
+3. **PKCE authorization code flow:** A localhost callback server is bound on an ephemeral port (or the port specified by
+   `oauth.callbackPort` if the server requires a fixed redirect URI). Your browser opens for login.
    The token is exchanged and stored in `<cache_dir>/oauth/mcp_<name>_oauth_tokens.json`.
 4. **Token injection:** On every connection to the server, Coyote loads the stored token (refreshing if expired) and injects
    it as an `Authorization: Bearer` header. No changes to `mcp.json` required.
@@ -196,13 +199,33 @@ If your organization pre-registers a client with the server (this is rare, as DC
     "my-server": {
       "type": "http",
       "url": "https://mcp.example.com/mcp",
-      "oauth_client_id": "your-registered-client-id"
+      "oauth": {
+        "clientId": "your-registered-client-id"
+      }
     }
   }
 }
 ```
 
-When `oauth_client_id` is set, DCR is skipped and the provided ID is used directly.
+When `oauth.clientId` is set, DCR is skipped and the provided ID is used directly.
+
+Some servers (e.g. Slack) pre-register an OAuth app with a specific redirect URI and require the callback to land on a
+fixed port. Use `oauth.callbackPort` in that case:
+
+```json
+{
+  "mcpServers": {
+    "slack": {
+      "type": "http",
+      "url": "https://mcp.slack.com/mcp",
+      "oauth": {
+        "clientId": "1601185624273.8899143856786",
+        "callbackPort": 3118
+      }
+    }
+  }
+}
+```
 
 ### Using a static token instead of OAuth
 
diff --git a/REPL.md b/REPL.md
index 74e559c..79ce622 100644
--- a/REPL.md
+++ b/REPL.md
@@ -352,7 +352,7 @@ where `<server-name>` matches the key in your `mcp.json` file. Tab completion is
 
 **What happens:**
 1. Coyote discovers the server's OAuth endpoints automatically via [RFC 9728](https://www.rfc-editor.org/rfc/rfc9728) metadata discovery.
-2. If the server supports [Dynamic Client Registration (RFC 7591)](https://www.rfc-editor.org/rfc/rfc7591), Coyote registers itself automatically, meaning no `oauth_client_id` configuration is required.
+2. If the server supports [Dynamic Client Registration (RFC 7591)](https://www.rfc-editor.org/rfc/rfc7591), Coyote registers itself automatically, meaning no `oauth.clientId` configuration is required.
 3. Your browser opens to the server's authorization page. Log in and approve access.
 4. The token is saved to `<cache_dir>/coyote/oauth/` and loaded automatically on subsequent startups.
 5. Tokens are refreshed automatically when they expire.