docs: add ability to use headers to print query plans (#2804)

Update docs on what headers can be set to return query plans in extensions --------- Co-authored-by: Maria Elisabeth Schreiber <[email protected]>
apollographql · Dec 5, 2023 · 28d1709 · 28d1709
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diff --git a/docs/source/query-plans.mdx b/docs/source/query-plans.mdx
@@ -444,6 +444,15 @@ You can view the query plan for a particular operation in any of the following w
     * Note that you must [register your federated graph](./managed-federation/setup/) with GraphOS to view query plans in the Explorer.
 * As direct output from the `@apollo/gateway` library (see below)
 
+### Outputting query plans with headers
+
+With [the Apollo Router](/router/) `v0.16.0+` and [`@apollo/gateway`](/apollo-server/using-federation/api/apollo-gateway/) `v2.5.4+`, you can pass the following headers to return the query plans in the GraphQL response extensions:
+
+* Including the `Apollo-Query-Plan-Experimental` header returns the query plan in the response extensions
+* Additionally including the `Apollo-Query-Plan-Experimental-Format` header with one of the supported options changes the output format:
+  * A value of `prettified` returns a human-readable string  of the query plan
+  * A value of `internal` returns a JSON representation of the query plan
+
 ### Outputting query plans with `@apollo/gateway`
 
 Your gateway can output the query plan for each incoming operation as it's calculated. To do so, add the following to the file where you initalize your `ApolloGateway` instance: