My Bicep deployment is demanding a "format" parameter when it's not even supported

Question

My Bicep deployment is demanding a "format" parameter when it's not even supported

Anonymous

I have a basic Bicep resource that I am trying to deploy and it fails every single time with an error that makes absolutely no sense:

"Value cannot be null. Parameter name: format"

"format" is not a parameter that this resource supports, so there's no discernable way to get around the error. This is my resource code:

param resourceName string
param userDefinedName string
param frequency int
param kind string
param locations array
param requestUrl string
param appInsightsResourceId string

resource webTest 'Microsoft.Insights/webTests@2022-06-15' = {
  name: resourceName
  location: resourceGroup().location
  properties: {
    Name: userDefinedName
    Enabled: true
    Frequency: frequency
    Kind: kind
    Locations: locations
    Request: {
      HttpVerb: 'GET'
      RequestUrl: requestUrl
    }
    RetryEnabled: false
    SyntheticMonitorId: userDefinedName
  }
  tags: {
    'hidden-link:${appInsightsResourceId}': 'Resource'
  }
}

output webTestId string = webTest.id

And my main.bicep file calls it like this:

module availabilityTest 'modules/insights/web-test.bicep' = {
  name: 'availability-test-deployment'
  params: {
    resourceName: healthCheckTestName
    userDefinedName: healthCheckTestName
    frequency: 300
    kind: 'standard'
    locations: [
      {
        Id: 'us-ca-sjc-azr' // West US
      }
      {
        Id: 'us-va-ash-azr' // East US
      }
      {
        Id: 'us-fl-mia-edge' // Central US
      }
      {
        Id: 'us-il-ch1-azr' // North Central US
      }
      {
        Id: 'us-tx-sn1-azr' // South Central US
      }
    ]
    requestUrl: 'http://${pip.outputs.publicIpAddress}/health'
    appInsightsResourceId: appi.outputs.appInsightsResourceId
  }
}

Ryan Hill 30,336 Reputation points Microsoft Employee Moderator

2025-04-02T21:17:12.4+00:00

@Stephen Baker this error may be getting generated from the ARM translation when your bicep is going through deployment. Can you add the -verbose switch to the CLI command? Hopefully, that will show more information about the error. Another thing you can do is build the bicep file and we can inspect the ARM template.

Answer accepted by question author

2 additional answers

Your answer

Ryan Hill 30,336 Reputation points Microsoft Employee Moderator

2025-04-02T21:17:12.4+00:00

@Stephen Baker this error may be getting generated from the ARM translation when your bicep is going through deployment. Can you add the -verbose switch to the CLI command? Hopefully, that will show more information about the error. Another thing you can do is build the bicep file and we can inspect the ARM template.

Answer 1

Hi @Stephen Baker
I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to "Accept " the answer.

Issue:
My Bicep deployment is demanding a "format" parameter when it's not even supported

Solution:
I was able to solve the issue by adding properties.ValidationRules to the resource. While they aren't stated to be required in the official documentation, it would seem that they are.

The final (working) resource definition looks like this. Hopefully this helps someone:

param resourceName string
param userDefinedName string
param description string
param frequency int
param timeout int = 30
param kind string
param locations array
param requestUrl string
param appInsightsResourceId string
resource webTest 'Microsoft.Insights/webtests@2022-06-15' = {
  name: resourceName
  kind: kind
  location: resourceGroup().location
  properties: {
    Name: userDefinedName
    Description: description
    Enabled: true
    Frequency: frequency
    Kind: kind
    Locations: locations
    Request: {
      HttpVerb: 'GET'
      RequestUrl: requestUrl
    }
    ValidationRules: {
      ExpectedHttpStatusCode: 200
      IgnoreHttpStatusCode: false
      ContentValidation: null
      SSLCheck: false
    }
    RetryEnabled: false
    SyntheticMonitorId: userDefinedName
    Timeout: timeout
  }
  tags: {
    'hidden-link:${appInsightsResourceId}': 'Resource'
  }
}
output webTestId string = webTest.id

If you have any other questions or are still running into more issues, please let me know. Thank you again for your time and patience throughout this issue.

Please remember to "Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.

Pranay Reddy Madireddy 6,340 Reputation points Moderator

2025-04-03T15:44:25.9533333+00:00

Hi Stephen Baker
Glad to know that your issue has been resolved. And thanks for sharing the solution, please don’t forget to close the thread by clicking "Accept the answer" wherever the information provided helps you, as this can be beneficial to other community members.

Answer 2

Alex Pike 10

If anyone else is STILL getting the deploy error "Value cannot be null. Parameter name: format" know that there are MULTIPLE hidden validation requirements. I can't list them all out here but for me, Timeout HAS to be 30. Frequency MUST be either 300, 600 or 900. ValidationRules.SSLCheck MUST be false if Request.RequestUrl is not https://

Almost destroyed myself deploying this resource. Will be sending the bill for my therapy sessions to whoever wrote the error handling for this resource.

0 comments

Answer 3

I was able to solve the issue by adding properties.ValidationRules to the resource. While they aren't stated to be required in the official documentation, it would seem that they are.

The final (working) resource definition looks like this. Hopefully this helps someone:

param resourceName string
param userDefinedName string
param description string
param frequency int
param timeout int = 30
param kind string
param locations array
param requestUrl string
param appInsightsResourceId string

resource webTest 'Microsoft.Insights/webtests@2022-06-15' = {
  name: resourceName
  kind: kind
  location: resourceGroup().location
  properties: {
    Name: userDefinedName
    Description: description
    Enabled: true
    Frequency: frequency
    Kind: kind
    Locations: locations
    Request: {
      HttpVerb: 'GET'
      RequestUrl: requestUrl
    }
    ValidationRules: {
      ExpectedHttpStatusCode: 200
      IgnoreHttpStatusCode: false
      ContentValidation: null
      SSLCheck: false
    }
    RetryEnabled: false
    SyntheticMonitorId: userDefinedName
    Timeout: timeout
  }
  tags: {
    'hidden-link:${appInsightsResourceId}': 'Resource'
  }
}

output webTestId string = webTest.id

CliveH 0 Reputation points

2026-04-05T20:10:06.99+00:00

Hi,
Like Alex, i have gone brain-dead trying to resolve this.
Given the error message is SOO poor, what exactly is causing this?

my bicep extract is

resource availabilityTest 'Microsoft.Insights/webtests@2022-06-15' = { name: availabilityTestName location: defaultLocation kind: 'ping' tags: union(tags, hiddenLinkTag) properties: { Enabled: true Frequency: 300 Timeout: 30 Kind: 'ping' RetryEnabled: true Locations: [ { Id: 'emea-nl-ams-azr' } { Id: 'emea-gb-db3-azr' } ] Request: { RequestUrl: 'https://${appServiceDefaultHostName}' HttpVerb: 'GET' ParseDependentRequests: false } ValidationRules: { ExpectedHttpStatusCode: 200 SSLCheck: true SSLCertRemainingLifetimeCheck: 30 IgnoreHttpStatusCode: false ContentValidation:null } Configuration: { WebTest: webTestXml } Name: availabilityTestName SyntheticMonitorId: availabilityTestName } }

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My Bicep deployment is demanding a "format" parameter when it's not even supported

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