diff --git a/.github/skills/github-mcp-server/SKILL.md b/.github/skills/github-mcp-server/SKILL.md
index 446712929c7..fe16a523c0a 100644
--- a/.github/skills/github-mcp-server/SKILL.md
+++ b/.github/skills/github-mcp-server/SKILL.md
@@ -164,8 +164,9 @@ This section maps individual tools to their respective toolsets to help with mig
 
 When invoking `list_pull_requests` from workflow prompts/templates:
 - Default to a small page size (`perPage: 10` unless a smaller/larger value is justified).
-- Request `minimal_output: true` when the installed MCP server exposes that input (minimal output trims non-essential nested fields such as large `head`/`base` payloads).
-- Confirm parameter support in the method schema from `mcp list-tools` or the tool docs for your server version; if `minimal_output` is unavailable, rely on small `perPage` values.
+- On GitHub MCP server ≥ 1.6.0 with the `fields_param` feature (enabled automatically in Insiders mode), pass `fields: [number, title, state, html_url]` (or whichever top-level fields you need) to reduce response size. The same `fields` parameter is available on `list_issues`, `search_issues`, `search_pull_requests`, `list_commits`, `list_releases`, `search_code`, and `get_file_contents`.
+- On older servers, request `minimal_output: true` when the installed MCP server exposes that input (minimal output trims non-essential nested fields such as large `head`/`base` payloads).
+- Confirm parameter support in the method schema from `mcp list-tools` or the tool docs for your server version.
 
 ### Actions Toolset
 - `list_workflows` - List GitHub Actions workflows
@@ -178,7 +179,7 @@ When invoking `list_pull_requests` from workflow prompts/templates:
 - `get_code_scanning_alert` - Get details of a specific alert
 - `create_code_scanning_alert` - Create a code scanning alert
 
-When invoking `list_code_scanning_alerts` from workflow prompts/templates, always include `state: open` and `severity: critical,high`.
+When invoking `list_code_scanning_alerts` from workflow prompts/templates, always include `state: open` and `severity: critical,high` to bound the response size and avoid oversized payloads.
 
 ### Discussions Toolset
 - `list_discussions` - List discussions in a repository
diff --git a/actions/setup/md/github_mcp_tools_prompt.md b/actions/setup/md/github_mcp_tools_prompt.md
index c796fb446f0..b165eb0cae4 100644
--- a/actions/setup/md/github_mcp_tools_prompt.md
+++ b/actions/setup/md/github_mcp_tools_prompt.md
@@ -2,4 +2,8 @@
 The GitHub MCP server is read-only. Use GitHub MCP tools for all GitHub reads: listing and searching issues, pull requests, discussions, labels, milestones; reading workflow runs, jobs, and artifacts; accessing repository contents, code, and metadata. Do not use shell `gh` commands for GitHub API reads — `gh` is not authenticated.
 
 **Identity**: Do not call `get_me` — it returns 403 under the integration token. Read your identity (actor, repository, run ID) from the `<github-context>` block provided at the start of the prompt.
+
+**Code scanning queries**: When calling `list_code_scanning_alerts`, always include `state: open` and `severity: critical,high` to bound the response size and avoid oversized payloads.
+
+**Field selection (GitHub MCP server ≥ 1.6.0)**: When calling list/search tools that accept a `fields` parameter (`list_pull_requests`, `list_issues`, `search_issues`, `search_pull_requests`, `list_commits`, `list_releases`, `search_code`, `get_file_contents`), pass only the fields you need to reduce response size. Example: `list_pull_requests` with `fields: [number, title, state, html_url]`.
 </github-mcp-tools>
diff --git a/actions/setup/md/github_mcp_tools_with_safeoutputs_prompt.md b/actions/setup/md/github_mcp_tools_with_safeoutputs_prompt.md
index 74538541482..4d2815c2f29 100644
--- a/actions/setup/md/github_mcp_tools_with_safeoutputs_prompt.md
+++ b/actions/setup/md/github_mcp_tools_with_safeoutputs_prompt.md
@@ -2,4 +2,8 @@
 The GitHub MCP server is read-only. Use GitHub MCP tools for all GitHub reads: listing and searching issues, pull requests, discussions, labels, milestones; reading workflow runs, jobs, and artifacts; accessing repository contents, code, and metadata. Do not use shell `gh` commands for GitHub API reads — `gh` is not authenticated. Use safeoutputs tools for GitHub writes and completion signaling.
 
 **Identity**: Do not call `get_me` — it returns 403 under the integration token. Read your identity (actor, repository, run ID) from the `<github-context>` block provided at the start of the prompt.
+
+**Code scanning queries**: When calling `list_code_scanning_alerts`, always include `state: open` and `severity: critical,high` to bound the response size and avoid oversized payloads.
+
+**Field selection (GitHub MCP server ≥ 1.6.0)**: When calling list/search tools that accept a `fields` parameter (`list_pull_requests`, `list_issues`, `search_issues`, `search_pull_requests`, `list_commits`, `list_releases`, `search_code`, `get_file_contents`), pass only the fields you need to reduce response size. Example: `list_pull_requests` with `fields: [number, title, state, html_url]`.
 </github-mcp-tools>
diff --git a/pkg/workflow/prompt_validation_test.go b/pkg/workflow/prompt_validation_test.go
index 2eea9455c49..34c2584cff0 100644
--- a/pkg/workflow/prompt_validation_test.go
+++ b/pkg/workflow/prompt_validation_test.go
@@ -12,6 +12,114 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+// TestGitHubMCPToolsPromptBoundsCodeScanningAlertQueries verifies that the
+// github_mcp_tools_prompt.md file includes the required guardrail instructing
+// agents to always bound list_code_scanning_alerts calls with state: open and
+// severity: critical,high. Unbounded queries produce oversized responses that
+// break downstream workflow runs.
+func TestGitHubMCPToolsPromptBoundsCodeScanningAlertQueries(t *testing.T) {
+	promptPath := filepath.Join("..", "..", "actions", "setup", "md", "github_mcp_tools_prompt.md")
+	data, err := os.ReadFile(promptPath)
+	require.NoError(t, err, "should be able to read github_mcp_tools_prompt.md")
+
+	content := string(data)
+
+	assert.Contains(t, content, "list_code_scanning_alerts",
+		"prompt should mention list_code_scanning_alerts to set agent expectations")
+	assert.Contains(t, content, "state: open",
+		"prompt should require state: open to bound list_code_scanning_alerts queries")
+	assert.Contains(t, content, "severity: critical,high",
+		"prompt should require severity: critical,high to bound list_code_scanning_alerts queries")
+}
+
+// TestGitHubMCPToolsWithSafeOutputsPromptBoundsCodeScanningAlertQueries verifies that
+// the github_mcp_tools_with_safeoutputs_prompt.md file includes the same guardrail.
+func TestGitHubMCPToolsWithSafeOutputsPromptBoundsCodeScanningAlertQueries(t *testing.T) {
+	promptPath := filepath.Join("..", "..", "actions", "setup", "md", "github_mcp_tools_with_safeoutputs_prompt.md")
+	data, err := os.ReadFile(promptPath)
+	require.NoError(t, err, "should be able to read github_mcp_tools_with_safeoutputs_prompt.md")
+
+	content := string(data)
+
+	assert.Contains(t, content, "list_code_scanning_alerts",
+		"prompt should mention list_code_scanning_alerts to set agent expectations")
+	assert.Contains(t, content, "state: open",
+		"prompt should require state: open to bound list_code_scanning_alerts queries")
+	assert.Contains(t, content, "severity: critical,high",
+		"prompt should require severity: critical,high to bound list_code_scanning_alerts queries")
+}
+
+// TestGitHubMCPToolsPromptHasFieldSelectionGuidance verifies that both prompt files
+// contain guidance about the fields parameter introduced in GitHub MCP server 1.6.0.
+// Field selection allows agents to request only the fields they need, significantly
+// reducing response size for list/search tools.
+func TestGitHubMCPToolsPromptHasFieldSelectionGuidance(t *testing.T) {
+	promptFiles := []string{
+		filepath.Join("..", "..", "actions", "setup", "md", "github_mcp_tools_prompt.md"),
+		filepath.Join("..", "..", "actions", "setup", "md", "github_mcp_tools_with_safeoutputs_prompt.md"),
+	}
+
+	for _, promptPath := range promptFiles {
+		t.Run(filepath.Base(promptPath), func(t *testing.T) {
+			data, err := os.ReadFile(promptPath)
+			require.NoError(t, err, "should be able to read %s", promptPath)
+
+			content := string(data)
+
+			assert.Contains(t, content, "fields",
+				"prompt should mention fields parameter for response size reduction")
+			assert.Contains(t, content, "list_pull_requests",
+				"prompt should reference list_pull_requests as a tool that supports fields")
+			assert.Contains(t, content, "1.6.0",
+				"prompt should reference the GitHub MCP server version that introduced fields")
+		})
+	}
+}
+
+// TestGitHubMCPToolsPromptIncludedForCodeSecurityToolset verifies that when a
+// workflow uses the code_security GitHub toolset the generated lock file references
+// one of the github_mcp_tools prompt files (which carry the list_code_scanning_alerts
+// guardrail). This is a regression test for unbounded alert queries.
+func TestGitHubMCPToolsPromptIncludedForCodeSecurityToolset(t *testing.T) {
+	tmpDir, err := os.MkdirTemp("", "gh-aw-code-scanning-prompt-test-*")
+	require.NoError(t, err)
+	defer os.RemoveAll(tmpDir)
+
+	testFile := filepath.Join(tmpDir, "test-workflow.md")
+	testContent := `---
+on: push
+engine: claude
+permissions:
+  security-events: read
+tools:
+  github:
+    toolsets: [code_security]
+---
+
+# Test Workflow with Code Security Toolset
+
+List open critical code scanning alerts.
+`
+	require.NoError(t, os.WriteFile(testFile, []byte(testContent), 0644))
+
+	compiler := NewCompiler()
+	require.NoError(t, compiler.CompileWorkflow(testFile))
+
+	lockFile := strings.TrimSuffix(testFile, ".md") + ".lock.yml"
+	lockContent, err := os.ReadFile(lockFile)
+	require.NoError(t, err)
+
+	lockStr := string(lockContent)
+
+	// The generated workflow must reference one of the github_mcp_tools prompt files
+	// (plain or with_safeoutputs variant) so the list_code_scanning_alerts guardrail
+	// is injected at runtime. Both variants carry the same guardrail.
+	hasGitHubMCPPrompt := strings.Contains(lockStr, githubMCPToolsPromptFile) ||
+		strings.Contains(lockStr, githubMCPToolsWithSafeOutputsPromptFile)
+	assert.True(t, hasGitHubMCPPrompt,
+		"lock file should reference a github_mcp_tools prompt file when code_security toolset is active")
+}
+
 // TestGeneratedWorkflowsValidatePromptStep tests that all generated workflows
 // include the prompt validation step
 func TestGeneratedWorkflowsValidatePromptStep(t *testing.T) {