feat(json-reporter): make compact output the default

- Change JSON reporter default from prettyPrint: true to false
- Add --json-pretty CLI flag to opt-in to formatted output
- Support reporterConfig.json.prettyPrint in config files
- CLI flag takes precedence over config file setting
- Derive ReporterConfig and JsonReporterConfig from Zod schemas
- Add TODO for ThresholdConfig schema derivation
- Add integration tests for CLI flag and config precedence

BREAKING CHANGE: JSON reporter now outputs compact JSON by default.
Use --json-pretty flag or set reporterConfig.json.prettyPrint: true
in config file to get formatted output.

Closes #74

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

Co-Authored-By: Claude <[email protected]>

Author: boneskull

src/cli/commands/run.ts

@@ -11,6 +11,7 @@ import type {
   BenchmarkRun,
   ModestBenchConfig,
   Reporter,
+  ReporterConfig,
 } from '../../types/index.js';
 import type { CliContext } from '../index.js';
 
@@ -61,6 +62,7 @@ interface RunOptions {
   excludeTags?: string[] | undefined;
   iterations?: number | undefined;
   json?: boolean | undefined;
+  jsonPretty?: boolean | undefined;
   noColor?: boolean | undefined;
   outputDir?: string | undefined;
   outputFile?: string | undefined;
@@ -126,6 +128,7 @@ export const handleRunCommand = async (
       options.outputDir,
       options.outputFile,
       options.progress,
+      options.jsonPretty,
     );
 
     // Step 3: Discovery phase
@@ -389,7 +392,7 @@ const setupReporters = async (
   context: CliContext,
   config: {
     outputDir?: string;
-    reporterConfig?: Record<string, unknown>;
+    reporterConfig?: ReporterConfig;
     reporters?: string[];
   },
   isVerbose: boolean,
@@ -398,6 +401,7 @@ const setupReporters = async (
   explicitOutputDir?: string,
   explicitOutputFile?: string,
   progressOption?: boolean,
+  explicitJsonPretty?: boolean,
 ): Promise<Reporter[]> => {
   try {
     const reporters: Reporter[] = [];
@@ -453,9 +457,14 @@ const setupReporters = async (
               explicitOutputFile,
               'results.json',
             );
+            // Precedence: CLI flag > config file > default (false)
+            const prettyPrint =
+              explicitJsonPretty ??
+              config.reporterConfig?.json?.prettyPrint ??
+              false;
             reporter = new JsonReporter({
               ...(outputPath ? { outputPath } : {}),
-              prettyPrint: true,
+              prettyPrint,
             });
             break;
           }

src/cli/index.ts

@@ -276,6 +276,12 @@ export const main = async (
                 'Benchmark engine: tinybench (default) or accurate (requires --allow-natives-syntax)',
               type: 'string',
             })
+            .option('json-pretty', {
+              defaultDescription: 'false',
+              description:
+                'Pretty-print JSON output (only affects json reporter)',
+              type: 'boolean',
+            })
             .example([
               ['$0 run', 'Run benchmarks in current directory and bench/'],
               ['$0 run benchmarks/', 'Run all benchmarks in a directory'],
@@ -315,6 +321,7 @@ export const main = async (
             excludeTags: argv['exclude-tag'],
             iterations: argv.iterations,
             json: argv.json,
+            jsonPretty: argv['json-pretty'],
             noColor: argv.noColor,
             outputDir: argv.output,
             outputFile: argv['output-file'],
@@ -1133,7 +1140,7 @@ const createCliContext = async (
     engine.registerReporter(
       'json',
       new JsonReporter({
-        prettyPrint: true,
+        prettyPrint: false,
       }),
     );
 

src/config/schema.ts

@@ -8,11 +8,36 @@
 
 import * as z from 'zod';
 
-import type { ModestBenchConfig } from '../types/core.js';
-
 import { BENCHMARK_FILE_PATTERN } from '../constants.js';
 import { parsePercentageString, parseTimeString } from './budget-schema.js';
 
+/**
+ * Schema for JSON reporter configuration options
+ */
+export const jsonReporterConfigSchema = z.object({
+  prettyPrint: z
+    .boolean()
+    .optional()
+    .describe('Whether to pretty-print JSON output (default: false)'),
+});
+
+/**
+ * Schema for reporter-specific configuration
+ *
+ * Allows typed configuration for known reporters while permitting unknown
+ * reporter configs via catchall.
+ */
+export const reporterConfigSchema = z
+  .object({
+    json: jsonReporterConfigSchema
+      .optional()
+      .describe('Configuration options for the JSON reporter'),
+  })
+  .catchall(z.unknown())
+  .describe(
+    'Configuration options specific to individual reporters, keyed by reporter name',
+  );
+
 /**
  * Schema for threshold configuration
  *
@@ -226,11 +251,7 @@ const modestBenchConfigSchema = z
       .describe(
         'Run in quiet mode with minimal console output (only errors and final results)',
       ),
-    reporterConfig: z
-      .record(z.string(), z.unknown())
-      .describe(
-        'Configuration options specific to individual reporters, keyed by reporter name',
-      ),
+    reporterConfig: reporterConfigSchema,
     reporters: z
       .array(z.string())
       .min(1)
@@ -446,3 +467,5 @@ export const safeParseConfig = (config: unknown) => {
 
   return result;
 };
+
+export type ModestBenchConfig = z.infer<typeof modestBenchConfigSchema>;

src/reporters/json.ts

@@ -90,7 +90,7 @@ export class JsonReporter extends BaseReporter {
     super('json', options);
 
     this.outputPath = options.outputPath;
-    this.prettyPrint = options.prettyPrint ?? true;
+    this.prettyPrint = options.prettyPrint ?? false;
     this.includeStatistics = options.includeStatistics ?? true;
     this.includeMetadata = options.includeMetadata ?? true;
   }

src/services/config-manager.ts

@@ -198,7 +198,10 @@ export class ModestBenchConfigurationManager implements ConfigurationManager {
         );
       }
 
-      return validation.data;
+      // TODO: safeParseConfig transforms budgets from nested to flat format,
+      // but the schema type doesn't reflect this. Fix by defining a separate
+      // output type for the transformed config. (see #15)
+      return validation.data as ModestBenchConfig;
     } catch (error) {
       // Re-throw our custom errors
       if (

src/types/core.ts

@@ -1,3 +1,10 @@
+import type { z } from 'zod';
+
+import type {
+  jsonReporterConfigSchema,
+  ModestBenchConfig,
+  reporterConfigSchema,
+} from '../config/schema.js';
 // Budget-related types
 import type {
   AbsoluteBudget,
@@ -13,30 +20,6 @@ import type {
   TaskId,
 } from './budgets.js';
 
-export type {
-  AbsoluteBudget,
-  BaselineReference,
-  BaselineStorage,
-  BaselineSummaryData,
-  Budget,
-  BudgetResult,
-  BudgetSummary,
-  BudgetViolation,
-  RelativeBudget,
-  RunId,
-  TaskId,
-};
-
-// Re-export schema-derived types
-export type {
-  BenchmarkDefinition,
-  BenchmarkDefinitionInput,
-  BenchmarkSuite,
-  BenchmarkSuiteInput,
-  BenchmarkTask,
-  BenchmarkTaskInput,
-} from '../core/benchmark-schema.js';
-
 /**
  * Benchmark file structure after parsing
  */
@@ -51,21 +34,6 @@ export interface BenchmarkFile {
   readonly metadata: FileMetadata;
 }
 
-/**
- * ModestBench Core Types
- *
- * Defines the fundamental data structures used throughout the ModestBench
- * system. These types represent benchmark results, metadata, configuration, and
- * system state.
- *
- * Note: BenchmarkDefinition, BenchmarkSuite, and BenchmarkTask types are
- * derived from Zod schemas and re-exported from benchmark-schema.ts for type
- * safety and consistency.
- */
-
-// Re-export identifier helper functions
-export { createRunId, createTaskId } from '../utils/identifiers.js';
-
 /**
  * Represents a complete benchmark run across multiple files
  */
@@ -98,6 +66,22 @@ export interface BenchmarkRun {
   readonly tags?: string[];
 }
 
+export type {
+  AbsoluteBudget,
+  BaselineReference,
+  BaselineStorage,
+  BaselineSummaryData,
+  Budget,
+  BudgetResult,
+  BudgetSummary,
+  BudgetViolation,
+  RelativeBudget,
+  RunId,
+  TaskId,
+};
+
+export type { ModestBenchConfig };
+
 /**
  * CI/CD environment information
  */
@@ -116,6 +100,28 @@ export interface CiInfo {
   readonly pullRequest?: string;
 }
 
+/**
+ * ModestBench Core Types
+ *
+ * Defines the fundamental data structures used throughout the ModestBench
+ * system. These types represent benchmark results, metadata, configuration, and
+ * system state.
+ *
+ * Note: BenchmarkDefinition, BenchmarkSuite, and BenchmarkTask types are
+ * derived from Zod schemas and re-exported from benchmark-schema.ts for type
+ * safety and consistency.
+ */
+
+// Re-export schema-derived types
+export type {
+  BenchmarkDefinition,
+  BenchmarkDefinitionInput,
+  BenchmarkSuite,
+  BenchmarkSuiteInput,
+  BenchmarkTask,
+  BenchmarkTaskInput,
+} from '../core/benchmark-schema.js';
+
 /**
  * CPU information
  */
@@ -277,6 +283,11 @@ export interface GitInfo {
   readonly timestamp: Date;
 }
 
+/**
+ * Configuration options for the JSON reporter
+ */
+export type JsonReporterConfig = z.infer<typeof jsonReporterConfigSchema>;
+
 /**
  * Memory information
  */
@@ -289,69 +300,15 @@ export interface MemoryInfo {
   readonly used: number;
 }
 
+// Re-export identifier helper functions
+export { createRunId, createTaskId } from '../utils/identifiers.js';
 /**
- * Benchmark configuration
- *
- * The JSON Schema for this configuration is available at
- * `dist/schema/modestbench-config.schema.json` after building the project.
+ * Reporter-specific configuration
  *
- * Config files can optionally include a `$schema` property pointing to the
- * schema file for IDE autocomplete and validation support.
- *
- * @example
- *
- * ```json
- * {
- *   "$schema": "./node_modules/modestbench/dist/schema/modestbench-config.schema.json",
- *   "iterations": 1000,
- *   "reporters": ["human", "json"],
- *   "time": 5000
- * }
- * ```
+ * Provides typed configuration for known reporters. Unknown reporter configs
+ * are allowed via index signature.
  */
-export interface ModestBenchConfig {
-  readonly $schema?: string | undefined;
-  /** Whether to stop on first failure */
-  readonly bail: boolean;
-  /** Name of baseline to use for relative budget comparisons */
-  readonly baseline?: string | undefined;
-  /** How to handle budget violations: 'fail', 'warn', or 'report' */
-  readonly budgetMode?: 'fail' | 'report' | 'warn' | undefined;
-  /** Performance budgets mapped by task identifier */
-  readonly budgets?: Record<string, unknown> | undefined;
-  /** Patterns to exclude from discovery */
-  readonly exclude: string[];
-  /** Tags to exclude from execution */
-  readonly excludeTags: string[];
-  /** Default number of iterations per task */
-  readonly iterations: number;
-  /** How to limit benchmark execution: 'time', 'iterations', 'any', or 'all' */
-  readonly limitBy: 'all' | 'any' | 'iterations' | 'time';
-  /** Custom metadata to attach to runs */
-  readonly metadata: Record<string, unknown>;
-  /** Output directory for reports (undefined means stdout for data reporters) */
-  readonly outputDir?: string;
-  /** Pattern(s) for discovering benchmark files */
-  readonly pattern: string | string[];
-  /** Whether to run in quiet mode */
-  readonly quiet: boolean;
-  /** Configuration for specific reporters */
-  readonly reporterConfig: Record<string, unknown>;
-  /** Reporters to use for output */
-  readonly reporters: string[];
-  /** Tags to include (if empty, include all) */
-  readonly tags: string[];
-  /** Threshold configuration for performance assertions */
-  readonly thresholds: ThresholdConfig;
-  /** Maximum time to spend on each task in milliseconds */
-  readonly time: number;
-  /** Timeout for individual tasks in milliseconds */
-  readonly timeout: number;
-  /** Whether to run in verbose mode */
-  readonly verbose: boolean;
-  /** Number of warmup iterations before measurement */
-  readonly warmup: number;
-}
+export type ReporterConfig = z.infer<typeof reporterConfigSchema>;
 
 /**
  * Summary statistics for a benchmark run
@@ -441,6 +398,8 @@ export interface TaskResult {
 
 /**
  * Threshold configuration for performance assertions
+ *
+ * TODO: Derive from thresholdConfigSchema via z.infer (see #15)
  */
 export interface ThresholdConfig {
   /** Maximum allowed margin of error percentage */