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Unlike REST APIs, GraphQL APIs provide a flexible approach to querying and mutating data through a single endpoint. They allow clients to specify exactly what data is needed, reducing over-fetching and under-fetching issues common with REST APIs. GraphQL APIs can be modified to customize requests and responses for testing and debugging. This guide provides detailed steps to achieve this using Requestly.

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Modifying GraphQL Responses

In GraphQL, client interactions are typically managed through a single HTTP endpoint. The specific operation to execute is often indicated by the operationName field in the request payload. Example Request 
POST <https://www.example.com/graphqlapi>
{
  "operationName": "getUsers",
  "query": `
    query getUsers {
      users {
        id
        email
      }
    }
  `
}
To modify the response of a GraphQL API:

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Steps to Modify API Response

1

Open HTTP Rules

Navigate to the HTTP Rules section in the web or desktop app.
2

Create a New Rule

Click on ”+ New Rule” and select Modify API Response.
3

Configure Resource Type

Choose “GraphQL API” as the Resource Type.
4

Set GraphQL Operation Filter

In the GraphQL Operation (Request Payload Filter) section:
  • Enter Key as operationName.
  • Enter Value as the operation name you want to target (e.g., getUsers).
5

Customize Response

Define the new response you want to serve for the specified operation.
6

Save and Activate

Click Save to store the rule and toggle it ON to apply the changes.
7

Test the Rule

Validate the rule by sending a request matching your conditions and verifying the modified response.
For additional details, visit the Modify API Response Rule Page. Notes
  • The Key represents the JSON key in the request payload and supports nested paths. For example:
    • If operationName is located at data.operationName, specify data.operationName.
    • For array payloads, such as [{"operationName": "value"}], use 0.operationName as the key.
  • If the request does not include operationName, select Resource Type as “REST API” and use Dynamic (JavaScript) Mode to filter and modify the response.

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Example Without operationName

In cases where the operation is specified within the query field: 
POST /graphql
{
  "query": `
    query getUsers {
      users {
        id
        email
      }
    }
  `
}
You can modify the response using a JavaScript snippet: 
function modifyResponse(args) {
  const { url, response, requestData, responseJSON } = args;

  if (requestData.query?.includes("query getUsers")) {
    console.log("Requestly: Modifying response", { query: requestData.query });
    return { ...responseJSON, custom: true };
  }

  return response;
}

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Modifying GraphQL Requests

If you need to alter the GraphQL query or its variables, use the Modify Request Body rule to change the request payload dynamically.

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Steps to Modify Request Body

1

Open HTTP Rules

Navigate to the HTTP Rules tab in the web or desktop app.
2

Create a New Rule

Click on ”+ New Rule” and select Modify Request Body.
3

Configure Resource Type

Choose “GraphQL API” as the Resource Type.
4

Set GraphQL Operation Filter

In the GraphQL Operation (Request Payload Filter) section:
  • Enter Key as operationName.
  • Enter Value as the operation name you want to target (e.g., getUsers).
5

Customize Request

Define the new Request you want to serve for the specified operation
6

Save and Activate

Click Save to store the rule and toggle it ON to apply the changes
7

Test the Rule

Validate the rule by sending a request matching your conditions and verifying the modified response.
For additional details, visit the Modify Request Rule Page.