{
  "id": "skill-router",
  "title": "Skill Router",
  "level": 2,
  "levelName": "Builder",
  "tagline": "Route a request to a skill using explainable keyword scores, path rules, permission gates, and dependency ordering.",
  "summary": "Route a request to a skill using explainable keyword scores, path rules, permission gates, and dependency ordering.",
  "hours": 8,
  "languages": [
    "TypeScript"
  ],
  "status": "ready",
  "source": "core",
  "author": {
    "name": "AI Engineering from Scratch",
    "github": "rohitg00"
  },
  "skills": [
    "Parse a typed skill catalog",
    "Score words and repository paths",
    "Resolve dependencies before execution",
    "Abstain on ambiguous or blocked requests"
  ],
  "prerequisites": [
    {
      "title": "Tool schema design",
      "path": "phases/13-tools-and-protocols/05-tool-schema-design"
    },
    {
      "title": "Verification gates",
      "path": "phases/14-agent-engineering/38-verification-gates"
    }
  ],
  "youWillBuild": "A routing debugger showing why the wrong skill activated and how to fix a rule.",
  "usefulFor": [
    "A routing debugger showing why the wrong skill activated and how to fix a rule.",
    "SKILL.md provides standard name and description; routing.json is this project's documented local extension."
  ],
  "demo": {
    "command": [
      "node",
      "demo.ts"
    ],
    "cwd": "solution"
  },
  "stages": [
    {
      "id": "01-catalog",
      "title": "Parse a typed skill catalog",
      "summary": "A skill manifest declares an id, description, keywords, path patterns, priority, dependencies and permissions. Validate arrays and numbers at runtime rather than trusting a JSON cast. Tokenization normalizes punctuation and case and removes repeated words, so repeating a prompt cannot inflate its score.",
      "hours": 2,
      "language": "typescript",
      "languageWhy": "TypeScript makes permission and dependency declarations visible before routing.",
      "concepts": [
        "parseSkill",
        "tokens"
      ],
      "difficulty": "starter",
      "requires": [
        "node"
      ],
      "timeout": 90,
      "figure": "pj-skill-router-1"
    },
    {
      "id": "02-score",
      "title": "Score words and repository paths",
      "summary": "Award two points for each matched keyword and three for each matched file path. Return score reasons alongside the score. Support star within one path segment and double-star across segments, escape regular expression punctuation, and reject absolute or parent-traversing file paths. Resolve tied scores by priority and then id so ranking is reproducible.",
      "hours": 2,
      "language": "typescript",
      "languageWhy": "Small pure scoring functions are easy to inspect in a terminal and reuse in a web UI.",
      "concepts": [
        "matchPath",
        "rank"
      ],
      "difficulty": "core",
      "requires": [
        "node"
      ],
      "timeout": 90,
      "figure": "pj-skill-router-2"
    },
    {
      "id": "03-dependencies",
      "title": "Resolve dependencies before execution",
      "summary": "Use depth-first traversal with separate active and visited sets. Active membership catches a cycle; visited membership avoids duplicate execution through a diamond. Validate permission requirements on dependencies as well as the selected skill. Emit dependencies before their consumers and reject unknown dependency ids instead of silently skipping work.",
      "hours": 2,
      "language": "typescript",
      "languageWhy": "A directed graph maps naturally onto typed arrays and sets.",
      "concepts": [
        "plan"
      ],
      "difficulty": "core",
      "requires": [
        "node"
      ],
      "timeout": 90,
      "figure": "pj-skill-router-3"
    },
    {
      "id": "04-route",
      "title": "Abstain on ambiguous or blocked requests",
      "summary": "Join ranking and dependency planning while preserving four distinct outcomes: ready, no-match, ambiguous and blocked. A score gap below the margin is ambiguous even if the tie-breaker produces a first result. A ranked winner can still be blocked by permissions. Return the ranked explanations in every outcome so a caller can display the decision.",
      "hours": 2,
      "language": "typescript",
      "languageWhy": "Discriminated status values prevent an uncertain route from becoming an execution request.",
      "concepts": [
        "route"
      ],
      "difficulty": "core",
      "requires": [
        "node"
      ],
      "timeout": 90,
      "figure": "pj-skill-router-4"
    }
  ],
  "demos": [
    {
      "gif": "media/run.gif",
      "poster": "media/run.png",
      "title": "Initialize and grade",
      "caption": "Recorded starter failure followed by all reference-solution stages passing. Reference passes do not earn learner certificates."
    },
    {
      "gif": "media/output.gif",
      "poster": "media/output.png",
      "title": "Inspect the output",
      "caption": "Actual output from the local deterministic demo command. See the README for fixture and live-adapter limits."
    }
  ]
}