Seshat

Seshat is a native CLI for TypeScript and TSX complexity analysis and mutation testing. check runs both assessments, crap runs complexity and coverage analysis, and mutate runs mutation testing from the original test baseline.

Install

Install the entry package in the project you want to assess:

npm install --save-dev @binary-balance/seshat

The package declares and verifies Node.js 24.20.0 exactly. It selects one native payload for the current platform from these five verified targets:

• Linux x64 (glibc; Debian 11 userspace, glibc 2.31)
• Linux ARM64 (glibc; Ubuntu 22.04, glibc 2.35)
• macOS x64 (macOS 15.0 minimum)
• macOS ARM64 (macOS 15.0 minimum)
• Windows x64 (Windows Server 2022 verification)

These are the known verification floors; see the native platform support matrix for the detailed target evidence.

Minimal mutation example

For a small Node test setup, install TypeScript in the project first:

npm install --save-dev typescript

Create src/rules.mts:

export function classify(value: number): 'positive' | 'negative' {
  return value >= 0 ? 'positive' : 'negative';
}

Create tests/rules.test.mjs:

import assert from 'node:assert/strict';
import {test} from 'node:test';
import {classify} from '../src/rules.mts';

test('classifies zero and positive values', () => {
  assert.equal(classify(0), 'positive');
  assert.equal(classify(1), 'positive');
});

Create tsconfig.json:

{
  "compilerOptions": {
    "strict": true,
    "noEmit": true,
    "skipLibCheck": true,
    "target": "ES2022",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "allowImportingTsExtensions": true
  },
  "include": ["src/**/*.mts"]
}

Create seshat.json:

{
  "source": {"include": ["src/**/*.mts"]},
  "capture": [
    "package.json",
    "package-lock.json",
    "tsconfig.json",
    "src",
    "tests",
    "node_modules"
  ],
  "setups": [{
    "name": "node",
    "runner": "node",
    "cwd": ".",
    "typecheck": [
      "node",
      "node_modules/typescript/bin/tsc",
      "--project",
      "tsconfig.json"
    ],
    "test": [
      "node",
      "--test",
      "--test-concurrency=1",
      "--test-reporter={seshatReporter}",
      "tests/rules.test.mjs"
    ],
    "coverage": {
      "command": ["node", "-e", "process.exit(0)"],
      "report": "coverage/unused.json"
    }
  }]
}

Run mutation testing and save its JSON report:

./node_modules/.bin/seshat mutate --config ./seshat.json \
  --json --no-progress > seshat-report.json

The coverage block is required by the configuration schema but is not run by mutate; the no-op command above keeps this example dependency-light. check and crap do run coverage and need a command that writes a fresh Istanbul JSON report. Use the complete Node example, Vitest example, or Jest/Expo example for those commands.

See the full configuration guide for all fields and runner setup, and the JSON report format for the --json output contract.