Merge pull request #139 from apollographql/gt-234-add-custom-scalars-config-docs

docs:Adding a section for custom scalars config file

Author: alocay

docs/source/command-reference.mdx

@@ -92,7 +92,7 @@ apollo-mcp-server [OPTIONS] --directory <DIRECTORY>
 |:------------------------------------------------------|:-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | `-d, --directory <DIRECTORY>`                         | The working directory to use. Defaults the current working directory.                                                                                                                                                                |
 | `-s, --schema <SCHEMA>`                               | The path to the GraphQL API schema file.                                                                                                                                                                                             |
-| `-c, --custom-scalars-config <CUSTOM_SCALARS_CONFIG>` | The path to the GraphQL custom_scalars_config file.                                                                                                                                                                                  |
+| `-c, --custom-scalars-config <CUSTOM_SCALARS_CONFIG>` | The path to the GraphQL custom_scalars_config file. [Learn more](/apollo-mcp-server/guides/#custom-scalars-configuration).                                                                                                           |
 | `-e, --endpoint <ENDPOINT>`                           | The GraphQL endpoint the server will invoke.<br />[default: `http://127.0.0.1:4000`]                                                                                                                                                 |
 | `--header <HEADERS>`                                  | Headers to send to the endpoint.                                                                                                                                                                                                     |
 | `--sse-port <SSE_PORT>`                               | Start the server using the SSE transport on the given port (default: 5000).                                                                                                                                                          |
@@ -101,7 +101,7 @@ apollo-mcp-server [OPTIONS] --directory <DIRECTORY>
 | `--http-address <HTTP_ADDRESS>`                       | The IP address to bind the Streamable HTTP server to (default: 127.0.0.1).                                                                                                                                                           |
 | `-i, --introspection`                                 | Expose the schema to the MCP client through `introspect` and `execute` tools. [Learn more](/apollo-mcp-server/guides/#from-schema-introspection).                                                                                    |
 | `-u, --uplink`                                        | Enable use of uplink to get the schema and persisted queries (requires `APOLLO_KEY` and `APOLLO_GRAPH_REF`). [Learn more](/apollo-mcp-server/guides/#from-graphos-managed-persisted-queries).                                        |
-| `-x, --explorer`                                      | Expose a tool that returns the URL to open a GraphQL operation in Apollo Explorer (requires `APOLLO_GRAPH_REF`).                                                                                                    |
+| `-x, --explorer`                                      | Expose a tool that returns the URL to open a GraphQL operation in Apollo Explorer (requires `APOLLO_GRAPH_REF`).                                                                                                                     |
 | `-o, --operations [<OPERATIONS>...]`                  | Operation files to expose as MCP tools. [Learn more](/apollo-mcp-server/guides/#from-operation-files).                                                                                                                               |
 | `--manifest <MANIFEST>`                               | The path to the persisted query manifest containing operations.                                                                                                                                                                      |
 | `--collection <COLLECTION_ID>`                        | The ID of an operation collection to use as the source for operations                                                                                                                                                                |

docs/source/guides/index.mdx

@@ -274,3 +274,22 @@ npx @modelcontextprotocol/inspector
     - **URL**: Enter `http://127.0.0.1:5000/mcp`, where the port must match the `--http-port` option
 
 1. Click **Connect** and **List Tools**. You should see the tools for the operations you provided.
+
+## Custom scalars configuration
+
+You can specify a custom scalars configuration JSON file to map a custom scalar to a [JSON schema type](https://json-schema.org/understanding-json-schema/reference/type). The JSON file is an object with custom scalar names as keys and JSON schema types as values:
+```json
+{
+   "MyCustomScalar": { "type": "string" }
+}
+```
+Other than JSON schema type, an overriding description can also be provided. In the following example the description provided in the schema, `scalar description`, would get overridden by the description found in the custom scalar configuration file, `override description`:
+```graphql
+"""scalar description"""
+scalar MyCustomScalar
+```
+```json
+{
+   "MyCustomScalar": { "type": "string", "description":  "override description" }
+}
+```