CircleCI

Developer ToolsPublisher: CircleCI

Route CircleCI MCP traffic through Formal to control and log what AI agents do in CircleCI:

Block risky tools, such as cancel_workflow.
Mask sensitive data in tool results, such as secrets and API keys in get_build_failure_logs responses.
Keep credentials at the Connector, so users and agents never see CircleCI tokens.
Log every tool call with the user, the MCP client and its parameters.

0. Prepare your Connector

The Connector needs an MCP listener and a hostname with wildcard DNS and TLS. Set them up once by following Deploy the Connector. Every MCP server reuses them.

1. Add CircleCI MCP server to your Resources

UI
Terraform
Pulumi
API

Open the Admin Catalog and click Add MCP.
Select the CircleCI template.
Enter a DNS-label Name, such as circleci.
Choose the Space containing your Connector, such as default.
Configure upstream authentication as described below, then save.

If no Connector is in the selected Space, the Configuration tab shows MCP clients can’t connect directly yet. The reason reads: No Connector is in this server's Space.

Set space_id to the ID of the Space containing your Connector.

resource "formal_resource" "circleci" {
  name                    = "circleci"
  technology              = "mcp"
  hostname                = "mcp.circleci.com"
  space_id                = "<SPACE_ID>"
  native_users_v3_enabled = true
  port                    = 443
  tags = {
    "mcp-endpoint" = "/v1/mcp"
  }
}

resource "formal_resource_oauth_settings" "circleci" {
  resource_id = formal_resource.circleci.id
}

Set spaceId to the ID of the Space containing your Connector.

import * as formal from "@formalco/pulumi";

const resource = new formal.Resource("mcp", {
  name: "circleci",
  technology: "mcp",
  hostname: "mcp.circleci.com",
  port: 443,
  spaceId: "<SPACE_ID>",
  tags: { "mcp-endpoint": "/v1/mcp" },
  nativeUsersV3Enabled: true,
});

new formal.ResourceOauthSettings("mcpOAuth", {
  resourceId: resource.id,
});

Create a Resource with the MCP endpoint and its Space ID.

export FORMAL_API_KEY="<YOUR_API_KEY>"
RESOURCE_RESPONSE=$(curl --fail --silent --show-error \
  --request POST \
  https://api.formal.ai/core.v1.ResourceService/CreateResource \
  --header "x-api-key: ${FORMAL_API_KEY}" \
  --header "Content-Type: application/json" \
  --data-binary @- <<JSON
  {
    "name": "circleci",
    "hostname": "mcp.circleci.com",
    "port": 443,
    "technology": "mcp",
    "spaceId": "<SPACE_ID>",
    "tags": [
      {
        "key": "mcp-endpoint",
        "value": "/v1/mcp"
      }
    ]
  }
JSON
)
RESOURCE_ID=$(printf '%s' "${RESOURCE_RESPONSE}" | jq -r '.resource.id')
curl --fail --silent --show-error \
  --request POST \
  https://api.formal.ai/core.v1.ResourceService/CreateResourceOAuthSettings \
  --header "x-api-key: ${FORMAL_API_KEY}" \
  --header "Content-Type: application/json" \
  --data-binary @- <<JSON
  {
    "resourceId": "${RESOURCE_ID}"
  }
JSON

2. Setup Authentication

Linked Accounts
Shared Credentials (Recommended)
Pass Through

Each user links their own CircleCI account once in the Employee Catalog, and the Connector sends that user’s token to CircleCI.

Linked Accounts selected under How does Formal authenticate to this resource?

CircleCI only registers OAuth clients with loopback redirect URIs, so it can’t use Formal’s Redirect URI.Linked Accounts isn’t available for CircleCI. Use Shared Credentials instead.

An administrator stores one CircleCI token in Formal, and the Connector sends it on every user’s requests without showing it to them.

Shared Credentials selected under How does Formal authenticate to this resource?

CircleCI’s MCP endpoint accepts a personal API token as a Bearer token. Create one at app.circleci.com/settings/user/tokens. Restrict the token owner’s project access; manually created personal API tokens inherit full read/write permissions.

Open this server from the Admin Catalog.
Select Configuration, then Authentication.
Choose Shared Credentials, then select Add credential.
Enter the credential, make it the default, and select Save authentication.

See Native Users.For HTTP Bearer authentication, enter the raw token. The Connector adds the Bearer prefix.In the Terraform tab, set native_users_v3_enabled = true on the Resource and upstream_oauth_mode = "none" on its OAuth settings.

variable "mcp_shared_credential" {
  type      = string
  sensitive = true
}

resource "formal_native_user_v3" "mcp_shared_credential" {
  resource_id = formal_resource.circleci.id
  label       = "shared-credential"

  http_bearer {
    header = "Authorization"
    token {
      literal_wo         = var.mcp_shared_credential
      literal_wo_version = 1
    }
  }
}

resource "formal_resource_native_user_selection" "mcp_shared_credential" {
  resource_id = formal_resource.circleci.id
  cel         = "\"${formal_native_user_v3.mcp_shared_credential.id}\""
}

3. Route Endpoint traffic

Auth is managed at the Connector level when you use Linked Accounts or Shared Credentials, so the Endpoint needs to forward the MCP traffic to it. Laptops and VMs with the Formal Endpoint keep using https://mcp.circleci.com/v1/mcp, and a network rule sends that traffic to the Connector.

UI
Terraform
Pulumi
API

Go to Network Rules and create a rule named circleci-mcp.
Paste this expression, set the rule to Active, then save:

{
  "condition": {
    "pre_tcp": process.is_agent,
    // Every MCP server added to Formal: process.is_agent && resource.technology == "mcp"
    "pre_tls": process.is_agent && hostname == "mcp.circleci.com",
    "post_tls": true
  },
  "outputs": {
    "forward_to_connector": true
  }
}

resource "formal_network_rule" "circleci_mcp" {
  name        = "circleci-mcp"
  description = "Forward CircleCI MCP traffic from agents to the Connector"
  status      = "active"

  # Every MCP server added to Formal: set pre_tls to process.is_agent && resource.technology == "mcp"
  cel_expression = <<-EOT
    {
      "condition": {
        "pre_tcp": process.is_agent,
        "pre_tls": process.is_agent && hostname == "mcp.circleci.com",
        "post_tls": true
      },
      "outputs": {
        "forward_to_connector": true
      }
    }
  EOT
}

import * as formal from "@formalco/pulumi";

new formal.NetworkRule("circleciMcp", {
  name: "circleci-mcp",
  description: "Forward CircleCI MCP traffic from agents to the Connector",
  status: "active",
  // Every MCP server added to Formal: set pre_tls to process.is_agent && resource.technology == "mcp"
  celExpression: `
    {
      "condition": {
        "pre_tcp": process.is_agent,
        "pre_tls": process.is_agent && hostname == "mcp.circleci.com",
        "post_tls": true
      },
      "outputs": {
        "forward_to_connector": true
      }
    }
  `,
});

export FORMAL_API_KEY="<YOUR_API_KEY>"
# Every MCP server added to Formal: set pre_tls to process.is_agent && resource.technology == "mcp"
CEL_EXPRESSION=$(cat <<'CEL'
{
  "condition": {
    "pre_tcp": process.is_agent,
    "pre_tls": process.is_agent && hostname == "mcp.circleci.com",
    "post_tls": true
  },
  "outputs": {
    "forward_to_connector": true
  }
}
CEL
)
jq -n --arg cel "${CEL_EXPRESSION}" '{
  name: "circleci-mcp",
  description: "Forward CircleCI MCP traffic from agents to the Connector",
  status: "active",
  celExpression: $cel
}' | curl --fail --silent --show-error \
  --request POST \
  https://api.formal.ai/core.v1.DesktopService/CreateDesktopRoutingRule \
  --header "x-api-key: ${FORMAL_API_KEY}" \
  --header "Content-Type: application/json" \
  --data-binary @-

The rule matches known agents only. See Identity headers.Cloud agents such as Claude, ChatGPT and Cursor Cloud Agents don’t run the Endpoint. Point them at this server’s Connector address, https://circleci.<connector-hostname>/mcp. Find it in the Admin Catalog: open CircleCI, then copy Connector address on the Configuration tab.

4. Create policies

Tools

The Admin Catalog lists these tools for CircleCI:

Tool	Description
`get_build_failure_logs`	Retrieve logs for failed build steps.
`find_flaky_tests`	Find flaky tests in a project.
`get_job_test_metadata`	Retrieve test metadata for a job.
`list_pipelines`	List project pipelines.
`get_pipeline`	Retrieve a pipeline.
`trigger_pipeline`	Trigger a pipeline.
`list_workflows`	List workflows in a pipeline.
`rerun_workflow`	Rerun a workflow.
`cancel_workflow`	Cancel a workflow.

Policies examples

Block a tool
Mask a tool's output

This policy blocks the tools that change data, so agents can only read CircleCI.

package formal.v2

import future.keywords.if
import future.keywords.in

write_tools := {
  "trigger_pipeline",
  "rerun_workflow",
  "cancel_workflow",
}

request := {
  "action": "block",
  "type": "block_with_custom_message",
  "message": "Writing to CircleCI is not allowed.",
} if {
  input.resource.name == "circleci"
  input.mcp.method == "tools/call"
  input.mcp.tool_name in write_tools
}

This policy replaces email addresses in results returned by get_build_failure_logs.

package formal.v2

import future.keywords.if
import future.keywords.in

email_pattern := `[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}`

response := {
  "action": "rewrite",
  "body": regex.replace(input.http.body, email_pattern, "[REDACTED-EMAIL]"),
  "reason": "Mask emails in CircleCI results",
} if {
  input.resource.name == "circleci"
  input.mcp.tool_name in {"get_build_failure_logs"}
  regex.match(email_pattern, input.http.body)
}

See MCP resources for the input.mcp fields and Rewrite Action for body rewrites.

5. Check the logs

Open Logs and search for resource.name:circleci. Each CircleCI tool call is one request log with the user, the MCP client and the tool. Open a log to see its tool parameters and the policies it triggered. A blocked write shows the block policy and its message. A masked search shows the rewrite policy.See Logs for search syntax and filters.

Troubleshooting

The agent says CircleCI rejected your credentials

The agent relays: circleci rejected your credentials. Link or re-link your circleci account in Formal…Cause: CircleCI no longer accepts the linked token, for example after the user revoked access in CircleCI.Fix: Link CircleCI again from the Employee Catalog.With Shared Credentials, the message asks the user to contact an administrator. Replace the token in the server’s Shared Credentials.

Laptop traffic doesn't appear in Logs

Cause: The Endpoint isn’t running, or the network rule doesn’t match the client.Fix: Check the Endpoint is connected. The rule above only matches known agents. Other clients, such as a browser, reach CircleCI directly unless the rule also matches them. See Network rules.

MCP clients can't connect directly yet

Cause: The Configuration tab lists the reason, most often No Connector is in this server's Space.Fix: Edit the server and choose the Space containing its Connector.

Getting Started

Example Use Cases

AI Governance

Configuring Formal

Integrations

Configuration

0. Prepare your Connector

1. Add CircleCI MCP server to your Resources

2. Setup Authentication

3. Route Endpoint traffic

4. Create policies

Tools

Policies examples

5. Check the logs

Troubleshooting

Next Steps

MCP Gateway

All MCP servers

​0. Prepare your Connector

​1. Add CircleCI MCP server to your Resources

​2. Setup Authentication

​3. Route Endpoint traffic

​4. Create policies

​Tools

​Policies examples

​5. Check the logs

​Troubleshooting

​Next Steps

MCP Gateway

All MCP servers

0. Prepare your Connector

1. Add CircleCI MCP server to your Resources

2. Setup Authentication

3. Route Endpoint traffic

4. Create policies

Tools

Policies examples

5. Check the logs

Troubleshooting

Next Steps