docs: update structured outputs documentation

Fixed test coverage gap where tests were only parsing JSON manually
without actually invoking the parseAndSetStructuredOutputs function.

Changes:
- Export parseAndSetStructuredOutputs for testing
- Rewrite tests to use spyOn() to mock @actions/core functions
- Add tests that actually call the function and verify:
  - core.setOutput() called with correct JSON string
  - core.info() called with correct field count
  - Error thrown when result exists but structured_output undefined
  - Error thrown when no result message exists
  - Handles special characters in field names (hyphens, dots, @ symbols)
  - Handles arrays and nested objects correctly
  - File errors propagate correctly

All 8 tests now properly test the actual implementation with full
coverage of success and error paths.

Addresses review comment: https://github.com/anthropics/claude-code-action/pull/683#discussion_r2539770213

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.github/workflows/test-structured-output.yml

@@ -0,0 +1,349 @@
+name: Test Structured Outputs
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  test-basic-types:
+    name: Test Basic Type Conversions
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+
+      - name: Test with explicit values
+        id: test
+        uses: ./base-action
+        with:
+          prompt: |
+            Run this command: echo "test"
+
+            Then return EXACTLY these values:
+            - text_field: "hello"
+            - number_field: 42
+            - boolean_true: true
+            - boolean_false: false
+          json_schema: |
+            {
+              "type": "object",
+              "properties": {
+                "text_field": {"type": "string"},
+                "number_field": {"type": "number"},
+                "boolean_true": {"type": "boolean"},
+                "boolean_false": {"type": "boolean"}
+              },
+              "required": ["text_field", "number_field", "boolean_true", "boolean_false"]
+            }
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          claude_args: "--allowedTools Bash"
+
+      - name: Verify outputs
+        run: |
+          # Parse the structured_output JSON
+          OUTPUT='${{ steps.test.outputs.structured_output }}'
+
+          # Test string pass-through
+          TEXT_FIELD=$(echo "$OUTPUT" | jq -r '.text_field')
+          if [ "$TEXT_FIELD" != "hello" ]; then
+            echo "❌ String: expected 'hello', got '$TEXT_FIELD'"
+            exit 1
+          fi
+
+          # Test number → string conversion
+          NUMBER_FIELD=$(echo "$OUTPUT" | jq -r '.number_field')
+          if [ "$NUMBER_FIELD" != "42" ]; then
+            echo "❌ Number: expected '42', got '$NUMBER_FIELD'"
+            exit 1
+          fi
+
+          # Test boolean → "true" conversion
+          BOOLEAN_TRUE=$(echo "$OUTPUT" | jq -r '.boolean_true')
+          if [ "$BOOLEAN_TRUE" != "true" ]; then
+            echo "❌ Boolean true: expected 'true', got '$BOOLEAN_TRUE'"
+            exit 1
+          fi
+
+          # Test boolean → "false" conversion
+          BOOLEAN_FALSE=$(echo "$OUTPUT" | jq -r '.boolean_false')
+          if [ "$BOOLEAN_FALSE" != "false" ]; then
+            echo "❌ Boolean false: expected 'false', got '$BOOLEAN_FALSE'"
+            exit 1
+          fi
+
+          echo "✅ All basic type conversions correct"
+
+  test-complex-types:
+    name: Test Arrays and Objects
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+
+      - name: Test complex types
+        id: test
+        uses: ./base-action
+        with:
+          prompt: |
+            Run: echo "ready"
+
+            Return EXACTLY:
+            - items: ["apple", "banana", "cherry"]
+            - config: {"key": "value", "count": 3}
+            - empty_array: []
+          json_schema: |
+            {
+              "type": "object",
+              "properties": {
+                "items": {
+                  "type": "array",
+                  "items": {"type": "string"}
+                },
+                "config": {"type": "object"},
+                "empty_array": {"type": "array"}
+              },
+              "required": ["items", "config", "empty_array"]
+            }
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          claude_args: "--allowedTools Bash"
+
+      - name: Verify JSON stringification
+        run: |
+          # Parse the structured_output JSON
+          OUTPUT='${{ steps.test.outputs.structured_output }}'
+
+          # Arrays should be JSON stringified
+          if ! echo "$OUTPUT" | jq -e '.items | length == 3' > /dev/null; then
+            echo "❌ Array not properly formatted"
+            echo "$OUTPUT" | jq '.items'
+            exit 1
+          fi
+
+          # Objects should be JSON stringified
+          if ! echo "$OUTPUT" | jq -e '.config.key == "value"' > /dev/null; then
+            echo "❌ Object not properly formatted"
+            echo "$OUTPUT" | jq '.config'
+            exit 1
+          fi
+
+          # Empty arrays should work
+          if ! echo "$OUTPUT" | jq -e '.empty_array | length == 0' > /dev/null; then
+            echo "❌ Empty array not properly formatted"
+            echo "$OUTPUT" | jq '.empty_array'
+            exit 1
+          fi
+
+          echo "✅ All complex types handled correctly"
+
+  test-edge-cases:
+    name: Test Edge Cases
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+
+      - name: Test edge cases
+        id: test
+        uses: ./base-action
+        with:
+          prompt: |
+            Run: echo "test"
+
+            Return EXACTLY:
+            - zero: 0
+            - empty_string: ""
+            - negative: -5
+            - decimal: 3.14
+          json_schema: |
+            {
+              "type": "object",
+              "properties": {
+                "zero": {"type": "number"},
+                "empty_string": {"type": "string"},
+                "negative": {"type": "number"},
+                "decimal": {"type": "number"}
+              },
+              "required": ["zero", "empty_string", "negative", "decimal"]
+            }
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          claude_args: "--allowedTools Bash"
+
+      - name: Verify edge cases
+        run: |
+          # Parse the structured_output JSON
+          OUTPUT='${{ steps.test.outputs.structured_output }}'
+
+          # Zero should be "0", not empty or falsy
+          ZERO=$(echo "$OUTPUT" | jq -r '.zero')
+          if [ "$ZERO" != "0" ]; then
+            echo "❌ Zero: expected '0', got '$ZERO'"
+            exit 1
+          fi
+
+          # Empty string should be empty (not "null" or missing)
+          EMPTY_STRING=$(echo "$OUTPUT" | jq -r '.empty_string')
+          if [ "$EMPTY_STRING" != "" ]; then
+            echo "❌ Empty string: expected '', got '$EMPTY_STRING'"
+            exit 1
+          fi
+
+          # Negative numbers should work
+          NEGATIVE=$(echo "$OUTPUT" | jq -r '.negative')
+          if [ "$NEGATIVE" != "-5" ]; then
+            echo "❌ Negative: expected '-5', got '$NEGATIVE'"
+            exit 1
+          fi
+
+          # Decimals should preserve precision
+          DECIMAL=$(echo "$OUTPUT" | jq -r '.decimal')
+          if [ "$DECIMAL" != "3.14" ]; then
+            echo "❌ Decimal: expected '3.14', got '$DECIMAL'"
+            exit 1
+          fi
+
+          echo "✅ All edge cases handled correctly"
+
+  test-name-sanitization:
+    name: Test Output Name Sanitization
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+
+      - name: Test special characters in field names
+        id: test
+        uses: ./base-action
+        with:
+          prompt: |
+            Run: echo "test"
+            Return EXACTLY: {test-result: "passed", item_count: 10}
+          json_schema: |
+            {
+              "type": "object",
+              "properties": {
+                "test-result": {"type": "string"},
+                "item_count": {"type": "number"}
+              },
+              "required": ["test-result", "item_count"]
+            }
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          claude_args: "--allowedTools Bash"
+
+      - name: Verify sanitized names work
+        run: |
+          # Parse the structured_output JSON
+          OUTPUT='${{ steps.test.outputs.structured_output }}'
+
+          # Hyphens should be preserved in the JSON
+          TEST_RESULT=$(echo "$OUTPUT" | jq -r '.["test-result"]')
+          if [ "$TEST_RESULT" != "passed" ]; then
+            echo "❌ Hyphenated name failed: expected 'passed', got '$TEST_RESULT'"
+            exit 1
+          fi
+
+          # Underscores should work
+          ITEM_COUNT=$(echo "$OUTPUT" | jq -r '.item_count')
+          if [ "$ITEM_COUNT" != "10" ]; then
+            echo "❌ Underscore name failed: expected '10', got '$ITEM_COUNT'"
+            exit 1
+          fi
+
+          echo "✅ Name sanitization works"
+
+  test-execution-file-structure:
+    name: Test Execution File Format
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+
+      - name: Run with structured output
+        id: test
+        uses: ./base-action
+        with:
+          prompt: "Run: echo 'complete'. Return: {done: true}"
+          json_schema: |
+            {
+              "type": "object",
+              "properties": {
+                "done": {"type": "boolean"}
+              },
+              "required": ["done"]
+            }
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          claude_args: "--allowedTools Bash"
+
+      - name: Verify execution file contains structured_output
+        run: |
+          FILE="${{ steps.test.outputs.execution_file }}"
+
+          # Check file exists
+          if [ ! -f "$FILE" ]; then
+            echo "❌ Execution file missing"
+            exit 1
+          fi
+
+          # Check for structured_output field
+          if ! jq -e '.[] | select(.type == "result") | .structured_output' "$FILE" > /dev/null; then
+            echo "❌ No structured_output in execution file"
+            cat "$FILE"
+            exit 1
+          fi
+
+          # Verify the actual value
+          DONE=$(jq -r '.[] | select(.type == "result") | .structured_output.done' "$FILE")
+          if [ "$DONE" != "true" ]; then
+            echo "❌ Wrong value in execution file"
+            exit 1
+          fi
+
+          echo "✅ Execution file format correct"
+
+  test-summary:
+    name: Summary
+    runs-on: ubuntu-latest
+    needs:
+      - test-basic-types
+      - test-complex-types
+      - test-edge-cases
+      - test-name-sanitization
+      - test-execution-file-structure
+    if: always()
+    steps:
+      - name: Generate Summary
+        run: |
+          echo "# Structured Output Tests (Optimized)" >> $GITHUB_STEP_SUMMARY
+          echo "" >> $GITHUB_STEP_SUMMARY
+          echo "Fast, deterministic tests using explicit prompts" >> $GITHUB_STEP_SUMMARY
+          echo "" >> $GITHUB_STEP_SUMMARY
+          echo "| Test | Result |" >> $GITHUB_STEP_SUMMARY
+          echo "|------|--------|" >> $GITHUB_STEP_SUMMARY
+          echo "| Basic Types | ${{ needs.test-basic-types.result == 'success' && '✅ PASS' || '❌ FAIL' }} |" >> $GITHUB_STEP_SUMMARY
+          echo "| Complex Types | ${{ needs.test-complex-types.result == 'success' && '✅ PASS' || '❌ FAIL' }} |" >> $GITHUB_STEP_SUMMARY
+          echo "| Edge Cases | ${{ needs.test-edge-cases.result == 'success' && '✅ PASS' || '❌ FAIL' }} |" >> $GITHUB_STEP_SUMMARY
+          echo "| Name Sanitization | ${{ needs.test-name-sanitization.result == 'success' && '✅ PASS' || '❌ FAIL' }} |" >> $GITHUB_STEP_SUMMARY
+          echo "| Execution File | ${{ needs.test-execution-file-structure.result == 'success' && '✅ PASS' || '❌ FAIL' }} |" >> $GITHUB_STEP_SUMMARY
+
+          # Check if all passed
+          ALL_PASSED=${{
+            needs.test-basic-types.result == 'success' &&
+            needs.test-complex-types.result == 'success' &&
+            needs.test-edge-cases.result == 'success' &&
+            needs.test-name-sanitization.result == 'success' &&
+            needs.test-execution-file-structure.result == 'success'
+          }}
+
+          if [ "$ALL_PASSED" = "true" ]; then
+            echo "" >> $GITHUB_STEP_SUMMARY
+            echo "## ✅ All Tests Passed" >> $GITHUB_STEP_SUMMARY
+          else
+            echo "" >> $GITHUB_STEP_SUMMARY
+            echo "## ❌ Some Tests Failed" >> $GITHUB_STEP_SUMMARY
+            exit 1
+          fi

README.md

@@ -13,6 +13,7 @@ A general-purpose [Claude Code](https://claude.ai/code) action for GitHub PRs an
 - 💬 **PR/Issue Integration**: Works seamlessly with GitHub comments and PR reviews
 - 🛠️ **Flexible Tool Access**: Access to GitHub APIs and file operations (additional tools can be enabled via configuration)
 - 📋 **Progress Tracking**: Visual progress indicators with checkboxes that dynamically update as Claude completes tasks
+- 📊 **Structured Outputs**: Get validated JSON results that automatically become GitHub Action outputs for complex automations
 - 🏃 **Runs on Your Infrastructure**: The action executes entirely on your own GitHub runner (Anthropic API calls go to your chosen provider)
 - ⚙️ **Simplified Configuration**: Unified `prompt` and `claude_args` inputs provide clean, powerful configuration aligned with Claude Code SDK
 

action.yml

@@ -113,6 +113,10 @@ inputs:
     description: "Newline-separated list of Claude Code plugin marketplace Git URLs to install from (e.g., 'https://github.com/user/marketplace1.git\nhttps://github.com/user/marketplace2.git')"
     required: false
     default: ""
+  json_schema:
+    description: "JSON schema for structured output validation. When provided, Claude will return validated JSON matching this schema. All fields are available in the structured_output output as a JSON string (use fromJSON() or jq to access fields)."
+    required: false
+    default: ""
 
 outputs:
   execution_file:
@@ -124,6 +128,9 @@ outputs:
   github_token:
     description: "The GitHub token used by the action (Claude App token if available)"
     value: ${{ steps.prepare.outputs.github_token }}
+  structured_output:
+    description: "JSON string containing all structured output fields when json_schema input is provided. Use fromJSON() to parse: fromJSON(steps.id.outputs.structured_output).field_name"
+    value: ${{ steps.claude-code.outputs.structured_output }}
 
 runs:
   using: "composite"
@@ -174,6 +181,7 @@ runs:
         TRACK_PROGRESS: ${{ inputs.track_progress }}
         ADDITIONAL_PERMISSIONS: ${{ inputs.additional_permissions }}
         CLAUDE_ARGS: ${{ inputs.claude_args }}
+        JSON_SCHEMA: ${{ inputs.json_schema }}
         ALL_INPUTS: ${{ toJson(inputs) }}
 
     - name: Install Base Action Dependencies
@@ -228,6 +236,7 @@ runs:
         INPUT_SHOW_FULL_OUTPUT: ${{ inputs.show_full_output }}
         INPUT_PLUGINS: ${{ inputs.plugins }}
         INPUT_PLUGIN_MARKETPLACES: ${{ inputs.plugin_marketplaces }}
+        JSON_SCHEMA: ${{ inputs.json_schema }}
 
         # Model configuration
         GITHUB_TOKEN: ${{ steps.prepare.outputs.GITHUB_TOKEN }}

base-action/action.yml

@@ -67,6 +67,14 @@ inputs:
     description: "Newline-separated list of Claude Code plugin marketplace Git URLs to install from (e.g., 'https://github.com/user/marketplace1.git\nhttps://github.com/user/marketplace2.git')"
     required: false
     default: ""
+  json_schema:
+    description: |
+      JSON schema for structured output validation. Claude must return JSON matching this schema
+      or the action will fail. All fields are returned in a single structured_output JSON string.
+
+      Access outputs via: fromJSON(steps.<step-id>.outputs.structured_output).<field_name>
+    required: false
+    default: ""
 
 outputs:
   conclusion:
@@ -75,6 +83,9 @@ outputs:
   execution_file:
     description: "Path to the JSON file containing Claude Code execution log"
     value: ${{ steps.run_claude.outputs.execution_file }}
+  structured_output:
+    description: "JSON string containing all structured output fields (use fromJSON() or jq to parse)"
+    value: ${{ steps.run_claude.outputs.structured_output }}
 
 runs:
   using: "composite"
@@ -111,7 +122,7 @@ runs:
       run: |
         if [ -z "${{ inputs.path_to_claude_code_executable }}" ]; then
           echo "Installing Claude Code..."
-          curl -fsSL https://claude.ai/install.sh | bash -s 2.0.42
+          curl -fsSL https://claude.ai/install.sh | bash -s 2.0.45
         else
           echo "Using custom Claude Code executable: ${{ inputs.path_to_claude_code_executable }}"
           # Add the directory containing the custom executable to PATH
@@ -141,6 +152,7 @@ runs:
         INPUT_SHOW_FULL_OUTPUT: ${{ inputs.show_full_output }}
         INPUT_PLUGINS: ${{ inputs.plugins }}
         INPUT_PLUGIN_MARKETPLACES: ${{ inputs.plugin_marketplaces }}
+        JSON_SCHEMA: ${{ inputs.json_schema }}
 
         # Provider configuration
         ANTHROPIC_API_KEY: ${{ inputs.anthropic_api_key }}

base-action/src/index.ts

@@ -28,8 +28,22 @@ async function run() {
       promptFile: process.env.INPUT_PROMPT_FILE || "",
     });
 
+    // Build claudeArgs with JSON schema if provided
+    let claudeArgs = process.env.INPUT_CLAUDE_ARGS || "";
+
+    // Add allowed tools if specified
+    if (process.env.INPUT_ALLOWED_TOOLS) {
+      claudeArgs += ` --allowedTools "${process.env.INPUT_ALLOWED_TOOLS}"`;
+    }
+
+    // Add JSON schema if specified (no escaping - parseShellArgs handles it)
+    if (process.env.JSON_SCHEMA) {
+      // Wrap in single quotes for parseShellArgs
+      claudeArgs += ` --json-schema '${process.env.JSON_SCHEMA}'`;
+    }
+
     await runClaude(promptConfig.path, {
-      claudeArgs: process.env.INPUT_CLAUDE_ARGS,
+      claudeArgs: claudeArgs.trim(),
       allowedTools: process.env.INPUT_ALLOWED_TOOLS,
       disallowedTools: process.env.INPUT_DISALLOWED_TOOLS,
       maxTurns: process.env.INPUT_MAX_TURNS,

base-action/src/run-claude.ts

@@ -1,7 +1,7 @@
 import * as core from "@actions/core";
 import { exec } from "child_process";
 import { promisify } from "util";
-import { unlink, writeFile, stat } from "fs/promises";
+import { unlink, writeFile, stat, readFile } from "fs/promises";
 import { createWriteStream } from "fs";
 import { spawn } from "child_process";
 import { parse as parseShellArgs } from "shell-quote";
@@ -122,6 +122,48 @@ export function prepareRunConfig(
   };
 }
 
+/**
+ * Parses structured_output from execution file and sets GitHub Action outputs
+ * Only runs if json_schema was explicitly provided by the user
+ * Exported for testing
+ */
+export async function parseAndSetStructuredOutputs(
+  executionFile: string,
+): Promise<void> {
+  try {
+    const content = await readFile(executionFile, "utf-8");
+    const messages = JSON.parse(content) as {
+      type: string;
+      structured_output?: Record<string, unknown>;
+    }[];
+
+    // Search backwards - result is typically last or second-to-last message
+    const result = messages.findLast(
+      (m) => m.type === "result" && m.structured_output,
+    );
+
+    if (!result?.structured_output) {
+      throw new Error(
+        `json_schema was provided but Claude did not return structured_output.\n` +
+          `Found ${messages.length} messages. Result exists: ${!!result}\n`,
+      );
+    }
+
+    // Set the complete structured output as a single JSON string
+    // This works around GitHub Actions limitation that composite actions can't have dynamic outputs
+    const structuredOutputJson = JSON.stringify(result.structured_output);
+    core.setOutput("structured_output", structuredOutputJson);
+    core.info(
+      `Set structured_output with ${Object.keys(result.structured_output).length} field(s)`,
+    );
+  } catch (error) {
+    if (error instanceof Error) {
+      throw error; // Preserve original error and stack trace
+    }
+    throw new Error(`Failed to parse structured outputs: ${error}`);
+  }
+}
+
 export async function runClaude(promptPath: string, options: ClaudeOptions) {
   const config = prepareRunConfig(promptPath, options);
 
@@ -308,8 +350,23 @@ export async function runClaude(promptPath: string, options: ClaudeOptions) {
       core.warning(`Failed to process output for execution metrics: ${e}`);
     }
 
-    core.setOutput("conclusion", "success");
     core.setOutput("execution_file", EXECUTION_FILE);
+
+    // Parse and set structured outputs only if user provided json_schema
+    if (process.env.JSON_SCHEMA) {
+      try {
+        await parseAndSetStructuredOutputs(EXECUTION_FILE);
+      } catch (error) {
+        const errorMessage =
+          error instanceof Error ? error.message : String(error);
+        core.setFailed(errorMessage);
+        core.setOutput("conclusion", "failure");
+        process.exit(1);
+      }
+    }
+
+    // Set conclusion to success if we reached here
+    core.setOutput("conclusion", "success");
   } else {
     core.setOutput("conclusion", "failure");
 

base-action/test/run-claude.test.ts

@@ -78,5 +78,19 @@ describe("prepareRunConfig", () => {
         "stream-json",
       ]);
     });
+
+    test("should include json-schema flag when provided", () => {
+      const options: ClaudeOptions = {
+        claudeArgs:
+          '--json-schema \'{"type":"object","properties":{"result":{"type":"boolean"}}}\'',
+      };
+
+      const prepared = prepareRunConfig("/tmp/test-prompt.txt", options);
+
+      expect(prepared.claudeArgs).toContain("--json-schema");
+      expect(prepared.claudeArgs).toContain(
+        '{"type":"object","properties":{"result":{"type":"boolean"}}}',
+      );
+    });
   });
 });

base-action/test/structured-output.test.ts

@@ -0,0 +1,158 @@
+#!/usr/bin/env bun
+
+import { describe, test, expect, afterEach, beforeEach, spyOn } from "bun:test";
+import { writeFile, unlink } from "fs/promises";
+import { tmpdir } from "os";
+import { join } from "path";
+import { parseAndSetStructuredOutputs } from "../src/run-claude";
+import * as core from "@actions/core";
+
+// Mock execution file path
+const TEST_EXECUTION_FILE = join(tmpdir(), "test-execution-output.json");
+
+// Helper to create mock execution file with structured output
+async function createMockExecutionFile(
+  structuredOutput?: Record<string, unknown>,
+  includeResult: boolean = true,
+): Promise<void> {
+  const messages: any[] = [
+    { type: "system", subtype: "init" },
+    { type: "turn", content: "test" },
+  ];
+
+  if (includeResult) {
+    messages.push({
+      type: "result",
+      cost_usd: 0.01,
+      duration_ms: 1000,
+      structured_output: structuredOutput,
+    });
+  }
+
+  await writeFile(TEST_EXECUTION_FILE, JSON.stringify(messages));
+}
+
+// Spy on core functions
+let setOutputSpy: any;
+let infoSpy: any;
+
+beforeEach(() => {
+  setOutputSpy = spyOn(core, "setOutput").mockImplementation(() => {});
+  infoSpy = spyOn(core, "info").mockImplementation(() => {});
+});
+
+describe("parseAndSetStructuredOutputs", () => {
+  afterEach(async () => {
+    setOutputSpy?.mockRestore();
+    infoSpy?.mockRestore();
+    try {
+      await unlink(TEST_EXECUTION_FILE);
+    } catch {
+      // Ignore if file doesn't exist
+    }
+  });
+
+  test("should set structured_output with valid data", async () => {
+    await createMockExecutionFile({
+      is_flaky: true,
+      confidence: 0.85,
+      summary: "Test looks flaky",
+    });
+
+    await parseAndSetStructuredOutputs(TEST_EXECUTION_FILE);
+
+    expect(setOutputSpy).toHaveBeenCalledWith(
+      "structured_output",
+      '{"is_flaky":true,"confidence":0.85,"summary":"Test looks flaky"}',
+    );
+    expect(infoSpy).toHaveBeenCalledWith(
+      "Set structured_output with 3 field(s)",
+    );
+  });
+
+  test("should handle arrays and nested objects", async () => {
+    await createMockExecutionFile({
+      items: ["a", "b", "c"],
+      config: { key: "value", nested: { deep: true } },
+    });
+
+    await parseAndSetStructuredOutputs(TEST_EXECUTION_FILE);
+
+    const callArgs = setOutputSpy.mock.calls[0];
+    expect(callArgs[0]).toBe("structured_output");
+    const parsed = JSON.parse(callArgs[1]);
+    expect(parsed).toEqual({
+      items: ["a", "b", "c"],
+      config: { key: "value", nested: { deep: true } },
+    });
+  });
+
+  test("should handle special characters in field names", async () => {
+    await createMockExecutionFile({
+      "test-result": "passed",
+      "item.count": 10,
+      "user@email": "test",
+    });
+
+    await parseAndSetStructuredOutputs(TEST_EXECUTION_FILE);
+
+    const callArgs = setOutputSpy.mock.calls[0];
+    const parsed = JSON.parse(callArgs[1]);
+    expect(parsed["test-result"]).toBe("passed");
+    expect(parsed["item.count"]).toBe(10);
+    expect(parsed["user@email"]).toBe("test");
+  });
+
+  test("should throw error when result exists but structured_output is undefined", async () => {
+    const messages = [
+      { type: "system", subtype: "init" },
+      { type: "result", cost_usd: 0.01, duration_ms: 1000 },
+    ];
+    await writeFile(TEST_EXECUTION_FILE, JSON.stringify(messages));
+
+    await expect(
+      parseAndSetStructuredOutputs(TEST_EXECUTION_FILE),
+    ).rejects.toThrow(
+      "json_schema was provided but Claude did not return structured_output",
+    );
+  });
+
+  test("should throw error when no result message exists", async () => {
+    const messages = [
+      { type: "system", subtype: "init" },
+      { type: "turn", content: "test" },
+    ];
+    await writeFile(TEST_EXECUTION_FILE, JSON.stringify(messages));
+
+    await expect(
+      parseAndSetStructuredOutputs(TEST_EXECUTION_FILE),
+    ).rejects.toThrow(
+      "json_schema was provided but Claude did not return structured_output",
+    );
+  });
+
+  test("should throw error with malformed JSON", async () => {
+    await writeFile(TEST_EXECUTION_FILE, "{ invalid json");
+
+    await expect(
+      parseAndSetStructuredOutputs(TEST_EXECUTION_FILE),
+    ).rejects.toThrow();
+  });
+
+  test("should throw error when file does not exist", async () => {
+    await expect(
+      parseAndSetStructuredOutputs("/nonexistent/file.json"),
+    ).rejects.toThrow();
+  });
+
+  test("should handle empty structured_output object", async () => {
+    await createMockExecutionFile({});
+
+    await parseAndSetStructuredOutputs(TEST_EXECUTION_FILE);
+
+    expect(setOutputSpy).toHaveBeenCalledWith("structured_output", "{}");
+    expect(infoSpy).toHaveBeenCalledWith(
+      "Set structured_output with 0 field(s)",
+    );
+  });
+});

docs/usage.md

@@ -80,6 +80,7 @@ jobs:
 | `path_to_bun_executable`         | Optional path to a custom Bun executable. Skips automatic Bun installation. Useful for Nix, custom containers, or specialized environments                                             | No       | ""            |
 | `plugin_marketplaces`            | Newline-separated list of Claude Code plugin marketplace Git URLs to install from (e.g., see example in workflow above). Marketplaces are added before plugin installation             | No       | ""            |
 | `plugins`                        | Newline-separated list of Claude Code plugin names to install (e.g., see example in workflow above). Plugins are installed before Claude Code execution                                | No       | ""            |
+| `json_schema`                    | JSON schema for structured output validation. See [Structured Outputs](#structured-outputs) section below                     | No       | ""            |
 
 ### Deprecated Inputs
 
@@ -185,6 +186,82 @@ For a comprehensive guide on migrating from v0.x to v1.0, including step-by-step
       Focus on the changed files in this PR.
 ```
 
+## Structured Outputs
+
+Get validated JSON results from Claude that automatically become GitHub Action outputs. This enables building complex automation workflows where Claude analyzes data and subsequent steps use the results.
+
+### Basic Example
+
+```yaml
+- name: Detect flaky tests
+  id: analyze
+  uses: anthropics/claude-code-action@v1
+  with:
+    anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+    prompt: |
+      Check the CI logs and determine if this is a flaky test.
+      Return: is_flaky (boolean), confidence (0-1), summary (string)
+    json_schema: |
+      {
+        "type": "object",
+        "properties": {
+          "is_flaky": {"type": "boolean"},
+          "confidence": {"type": "number"},
+          "summary": {"type": "string"}
+        },
+        "required": ["is_flaky"]
+      }
+
+- name: Retry if flaky
+  if: fromJSON(steps.analyze.outputs.structured_output).is_flaky == true
+  run: gh workflow run CI
+```
+
+### How It Works
+
+1. **Define Schema**: Provide a JSON schema in the `json_schema` input
+2. **Claude Executes**: Claude uses tools to complete your task
+3. **Validated Output**: Result is validated against your schema
+4. **JSON Output**: All fields are returned in a single `structured_output` JSON string
+
+### Accessing Structured Outputs
+
+All structured output fields are available in the `structured_output` output as a JSON string:
+
+**In GitHub Actions expressions:**
+
+```yaml
+if: fromJSON(steps.analyze.outputs.structured_output).is_flaky == true
+run: |
+  CONFIDENCE=${{ fromJSON(steps.analyze.outputs.structured_output).confidence }}
+```
+
+**In bash with jq:**
+
+```yaml
+- name: Process results
+  run: |
+    OUTPUT='${{ steps.analyze.outputs.structured_output }}'
+    IS_FLAKY=$(echo "$OUTPUT" | jq -r '.is_flaky')
+    SUMMARY=$(echo "$OUTPUT" | jq -r '.summary')
+```
+
+**Note**: Due to GitHub Actions limitations, composite actions cannot expose dynamic outputs. All fields are bundled in the single `structured_output` JSON string.
+
+### Complete Example
+
+See `examples/test-failure-analysis.yml` for a working example that:
+
+- Detects flaky test failures
+- Uses confidence thresholds in conditionals
+- Auto-retries workflows
+- Comments on PRs
+
+### Documentation
+
+For complete details on JSON Schema syntax and Agent SDK structured outputs:
+https://docs.claude.com/en/docs/agent-sdk/structured-outputs
+
 ## Ways to Tag @claude
 
 These examples show how to interact with Claude using comments in PRs and issues. By default, Claude will be triggered anytime you mention `@claude`, but you can customize the exact trigger phrase using the `trigger_phrase` input in the workflow.

examples/test-failure-analysis.yml

@@ -0,0 +1,133 @@
+name: Auto-Retry Flaky Tests
+
+# This example demonstrates using structured outputs to detect flaky test failures
+# and automatically retry them, reducing noise from intermittent failures.
+#
+# Use case: When CI fails, automatically determine if it's likely flaky and retry if so.
+
+on:
+  workflow_run:
+    workflows: ["CI"]
+    types: [completed]
+
+permissions:
+  contents: read
+  actions: write
+
+jobs:
+  detect-flaky:
+    runs-on: ubuntu-latest
+    if: ${{ github.event.workflow_run.conclusion == 'failure' }}
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Detect flaky test failures
+        id: detect
+        uses: anthropics/claude-code-action@main
+        with:
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          prompt: |
+            The CI workflow failed: ${{ github.event.workflow_run.html_url }}
+
+            Check the logs: gh run view ${{ github.event.workflow_run.id }} --log-failed
+
+            Determine if this looks like a flaky test failure by checking for:
+            - Timeout errors
+            - Race conditions
+            - Network errors
+            - "Expected X but got Y" intermittent failures
+            - Tests that passed in previous commits
+
+            Return:
+            - is_flaky: true if likely flaky, false if real bug
+            - confidence: number 0-1 indicating confidence level
+            - summary: brief one-sentence explanation
+          json_schema: |
+            {
+              "type": "object",
+              "properties": {
+                "is_flaky": {
+                  "type": "boolean",
+                  "description": "Whether this appears to be a flaky test failure"
+                },
+                "confidence": {
+                  "type": "number",
+                  "minimum": 0,
+                  "maximum": 1,
+                  "description": "Confidence level in the determination"
+                },
+                "summary": {
+                  "type": "string",
+                  "description": "One-sentence explanation of the failure"
+                }
+              },
+              "required": ["is_flaky", "confidence", "summary"]
+            }
+
+      # Auto-retry only if flaky AND high confidence (>= 0.7)
+      - name: Retry flaky tests
+        if: |
+          fromJSON(steps.detect.outputs.structured_output).is_flaky == true &&
+          fromJSON(steps.detect.outputs.structured_output).confidence >= 0.7
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          OUTPUT='${{ steps.detect.outputs.structured_output }}'
+          CONFIDENCE=$(echo "$OUTPUT" | jq -r '.confidence')
+          SUMMARY=$(echo "$OUTPUT" | jq -r '.summary')
+
+          echo "🔄 Flaky test detected (confidence: $CONFIDENCE)"
+          echo "Summary: $SUMMARY"
+          echo ""
+          echo "Triggering automatic retry..."
+
+          gh workflow run "${{ github.event.workflow_run.name }}" \
+            --ref "${{ github.event.workflow_run.head_branch }}"
+
+      # Low confidence flaky detection - skip retry
+      - name: Low confidence detection
+        if: |
+          fromJSON(steps.detect.outputs.structured_output).is_flaky == true &&
+          fromJSON(steps.detect.outputs.structured_output).confidence < 0.7
+        run: |
+          OUTPUT='${{ steps.detect.outputs.structured_output }}'
+          CONFIDENCE=$(echo "$OUTPUT" | jq -r '.confidence')
+
+          echo "⚠️ Possible flaky test but confidence too low ($CONFIDENCE)"
+          echo "Not retrying automatically - manual review recommended"
+
+      # Comment on PR if this was a PR build
+      - name: Comment on PR
+        if: github.event.workflow_run.event == 'pull_request'
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          OUTPUT='${{ steps.detect.outputs.structured_output }}'
+          IS_FLAKY=$(echo "$OUTPUT" | jq -r '.is_flaky')
+          CONFIDENCE=$(echo "$OUTPUT" | jq -r '.confidence')
+          SUMMARY=$(echo "$OUTPUT" | jq -r '.summary')
+
+          pr_number=$(gh pr list --head "${{ github.event.workflow_run.head_branch }}" --json number --jq '.[0].number')
+
+          if [ -n "$pr_number" ]; then
+            if [ "$IS_FLAKY" = "true" ]; then
+              TITLE="🔄 Flaky Test Detected"
+              ACTION="✅ Automatically retrying the workflow"
+            else
+              TITLE="❌ Test Failure"
+              ACTION="⚠️ This appears to be a real bug - manual intervention needed"
+            fi
+
+            gh pr comment "$pr_number" --body "$(cat <<EOF
+          ## $TITLE
+
+          **Analysis**: $SUMMARY
+          **Confidence**: $CONFIDENCE
+
+          $ACTION
+
+          [View workflow run](${{ github.event.workflow_run.html_url }})
+          EOF
+          )"
+          fi

src/modes/agent/index.ts

@@ -7,6 +7,7 @@ import { parseAllowedTools } from "./parse-tools";
 import { configureGitAuth } from "../../github/operations/git-config";
 import type { GitHubContext } from "../../github/context";
 import { isEntityContext } from "../../github/context";
+import { appendJsonSchemaArg } from "../../utils/json-schema";
 
 /**
  * Extract GitHub context as environment variables for agent mode
@@ -149,6 +150,9 @@ export const agentMode: Mode = {
       claudeArgs = `--mcp-config '${escapedOurConfig}'`;
     }
 
+    // Add JSON schema if provided
+    claudeArgs = appendJsonSchemaArg(claudeArgs);
+
     // Append user's claude_args (which may have more --mcp-config flags)
     claudeArgs = `${claudeArgs} ${userClaudeArgs}`.trim();
 

src/modes/tag/index.ts

@@ -15,6 +15,7 @@ import { isEntityContext } from "../../github/context";
 import type { PreparedContext } from "../../create-prompt/types";
 import type { FetchDataResult } from "../../github/data/fetcher";
 import { parseAllowedTools } from "../agent/parse-tools";
+import { appendJsonSchemaArg } from "../../utils/json-schema";
 
 /**
  * Tag mode implementation.
@@ -177,6 +178,9 @@ export const tagMode: Mode = {
     // Add required tools for tag mode
     claudeArgs += ` --allowedTools "${tagModeTools.join(",")}"`;
 
+    // Add JSON schema if provided
+    claudeArgs = appendJsonSchemaArg(claudeArgs);
+
     // Append user's claude_args (which may have more --mcp-config flags)
     if (userClaudeArgs) {
       claudeArgs += ` ${userClaudeArgs}`;

src/utils/json-schema.ts

@@ -0,0 +1,17 @@
+/**
+ * Appends JSON schema CLI argument if json_schema is provided
+ * Escapes schema for safe shell passing
+ */
+export function appendJsonSchemaArg(
+  claudeArgs: string,
+  jsonSchemaStr?: string,
+): string {
+  const schema = jsonSchemaStr || process.env.JSON_SCHEMA || "";
+  if (!schema) {
+    return claudeArgs;
+  }
+
+  // CLI validates schema - just escape for safe shell passing
+  const escapedSchema = schema.replace(/'/g, "'\\''");
+  return `${claudeArgs} --json-schema '${escapedSchema}'`;
+}