LLM Project Development

LLM Project Development Skill

Build production LLM applications using proven methodology from Karpathy's HN Time Capsule, Vercel d0, Manus, and Anthropic's research.

Core principle: Validate manually first, then build deterministic pipelines around the non-deterministic LLM core.

Supporting Documentation

All files under 500 lines per Anthropic best practices:

• references/ - Methodology foundations

  • case-studies.md - Karpathy, Vercel d0, Manus patterns
  • pipeline-patterns.md - Python/TypeScript code patterns
  • INDEX.md - Reference navigation

• examples/ - Grey Haven implementations

  • tanstack-pipeline.md - TanStack Start example
  • fastapi-pipeline.md - FastAPI backend example
  • INDEX.md - Examples navigation

• templates/ - Copy-paste starters

  • pipeline-template.ts - TypeScript pipeline
  • pipeline-template.py - Python pipeline

• checklists/ - Validation

  • llm-project-checklist.md - Pre-launch checklist

The Methodology

Phase 1: Task-Model Fit Analysis

Before writing any code, determine if LLMs are the right tool.

LLM-Suited Tasks

LLM-Unsuited Tasks (Use Traditional Code)

The Manual Prototype Step

CRITICAL: Before building automation, validate with the target model manually.

## Manual Validation Checklist
- [ ] Copy ONE real example into the LLM UI
- [ ] Test with the EXACT model you'll use in production
- [ ] Verify output quality meets requirements
- [ ] Note edge cases and failure modes
- [ ] Estimate cost per operation

## Example: Karpathy's Approach
1. Took ONE Hacker News thread
2. Pasted into ChatGPT with analysis prompt
3. Confirmed Opus 4.5 could do the task
4. THEN built automation pipeline

Phase 2: Pipeline Architecture

Design principle: Deterministic stages wrapping one non-deterministic core.

┌─────────────────────────────────────────────────────────────────┐
│                    DETERMINISTIC                                 │
│  ┌──────────┐    ┌──────────┐    ┌──────────┐    ┌──────────┐  │
│  │ ACQUIRE  │ →  │ PREPARE  │ →  │ PROCESS  │ →  │  RENDER  │  │
│  │ (fetch)  │    │ (format) │    │  (LLM)   │    │ (output) │  │
│  └──────────┘    └──────────┘    └──────────┘    └──────────┘  │
│       ↑              ↑               ↑              ↑          │
│  Deterministic  Deterministic  NON-DETERMINISTIC  Deterministic│
│  (retry safe)   (retry safe)   (cache results)   (retry safe) │
└─────────────────────────────────────────────────────────────────┘

Stage Details

TypeScript Pipeline Example (TanStack Start)

// lib/pipelines/content-analyzer.ts
import Anthropic from "@anthropic-ai/sdk";
import { z } from "zod";
import { existsSync, mkdirSync, writeFileSync, readFileSync } from "fs";
import { join } from "path";

// Stage 1: Schema definition
const AnalysisSchema = z.object({
  summary: z.string(),
  sentiment: z.enum(["positive", "neutral", "negative"]),
  topics: z.array(z.string()),
  action_items: z.array(z.string()),
});

type Analysis = z.infer<typeof AnalysisSchema>;

// Stage 2: Acquire - Get data from database
async function acquire(tenant_id: string, content_id: string) {
  const content = await db.query.contents.findFirst({
    where: and(
      eq(contents.tenant_id, tenant_id),
      eq(contents.id, content_id)
    ),
  });

  if (!content) throw new Error(`Content ${content_id} not found`);
  return content;
}

// Stage 3: Prepare - Format prompt
function prepare(content: Content): string {
  return `Analyze this content and provide structured output.

CONTENT:
${content.body}

Respond with JSON matching this schema:
{
  "summary": "2-3 sentence summary",
  "sentiment": "positive" | "neutral" | "negative",
  "topics": ["topic1", "topic2"],
  "action_items": ["action1", "action2"]
}`;
}

// Stage 4: Process - LLM call with caching
async function process(
  prompt: string,
  cacheDir: string,
  cacheKey: string
): Promise<string> {
  const cachePath = join(cacheDir, `${cacheKey}.json`);

  // Check cache first
  if (existsSync(cachePath)) {
    return JSON.parse(readFileSync(cachePath, "utf-8")).response;
  }

  const client = new Anthropic();
  const response = await client.messages.create({
    model: "claude-sonnet-4-20250514",
    max_tokens: 1024,
    messages: [{ role: "user", content: prompt }],
  });

  const text = response.content[0].type === "text"
    ? response.content[0].text
    : "";

  // Cache result
  mkdirSync(cacheDir, { recursive: true });
  writeFileSync(cachePath, JSON.stringify({
    response: text,
    timestamp: new Date().toISOString()
  }));

  return text;
}

// Stage 5: Parse - Validate with Zod
function parse(response: string): Analysis {
  const jsonMatch = response.match(/\{[\s\S]*\}/);
  if (!jsonMatch) throw new Error("No JSON found in response");

  const parsed = JSON.parse(jsonMatch[0]);
  return AnalysisSchema.parse(parsed);
}

// Stage 6: Render - Save to database
async function render(
  tenant_id: string,
  content_id: string,
  analysis: Analysis
) {
  await db.update(contents)
    .set({
      analysis_summary: analysis.summary,
      analysis_sentiment: analysis.sentiment,
      analysis_topics: analysis.topics,
      updated_at: new Date(),
    })
    .where(and(
      eq(contents.tenant_id, tenant_id),
      eq(contents.id, content_id)
    ));

  return analysis;
}

// Main pipeline function
export async function analyzeContent(
  tenant_id: string,
  content_id: string
): Promise<Analysis> {
  const cacheDir = join(process.cwd(), ".cache", "analyses", tenant_id);

  const content = await acquire(tenant_id, content_id);
  const prompt = prepare(content);
  const response = await process(prompt, cacheDir, content_id);
  const analysis = parse(response);
  await render(tenant_id, content_id, analysis);

  return analysis;
}

Python Pipeline Example (FastAPI)

# app/pipelines/content_analyzer.py
from pathlib import Path
from pydantic import BaseModel
from anthropic import Anthropic
import json

class Analysis(BaseModel):
    summary: str
    sentiment: str  # positive | neutral | negative
    topics: list[str]
    action_items: list[str]

class ContentAnalyzerPipeline:
    def __init__(self, tenant_id: str, cache_dir: Path | None = None):
        self.tenant_id = tenant_id
        self.cache_dir = cache_dir or Path(".cache/analyses") / tenant_id
        self.client = Anthropic()

    async def acquire(self, content_id: str, db: AsyncSession) -> Content:
        """Stage 1: Get content from database."""
        result = await db.execute(
            select(Content).where(
                Content.tenant_id == self.tenant_id,
                Content.id == content_id
            )
        )
        content = result.scalar_one_or_none()
        if not content:
            raise ValueError(f"Content {content_id} not found")
        return content

    def prepare(self, content: Content) -> str:
        """Stage 2: Format prompt."""
        return f"""Analyze this content and provide structured output.

CONTENT:
{content.body}

Respond with JSON:
{{
  "summary": "2-3 sentence summary",
  "sentiment": "positive" | "neutral" | "negative",
  "topics": ["topic1", "topic2"],
  "action_items": ["action1"]
}}"""

    async def process(self, prompt: str, cache_key: str) -> str:
        """Stage 3: LLM call with file-based caching."""
        cache_path = self.cache_dir / f"{cache_key}.json"

        # Check cache
        if cache_path.exists():
            return json.loads(cache_path.read_text())["response"]

        response = self.client.messages.create(
            model="claude-sonnet-4-20250514",
            max_tokens=1024,
            messages=[{"role": "user", "content": prompt}]
        )

        text = response.content[0].text

        # Cache result
        self.cache_dir.mkdir(parents=True, exist_ok=True)
        cache_path.write_text(json.dumps({
            "response": text,
            "timestamp": datetime.utcnow().isoformat()
        }))

        return text

    def parse(self, response: str) -> Analysis:
        """Stage 4: Parse and validate with Pydantic."""
        import re
        match = re.search(r'\{[\s\S]*\}', response)
        if not match:
            raise ValueError("No JSON found in response")
        return Analysis.model_validate_json(match.group())

    async def render(
        self,
        content_id: str,
        analysis: Analysis,
        db: AsyncSession
    ) -> Analysis:
        """Stage 5: Save to database."""
        await db.execute(
            update(Content)
            .where(
                Content.tenant_id == self.tenant_id,
                Content.id == content_id
            )
            .values(
                analysis_summary=analysis.summary,
                analysis_sentiment=analysis.sentiment,
                analysis_topics=analysis.topics,
                updated_at=datetime.utcnow()
            )
        )
        await db.commit()
        return analysis

    async def run(self, content_id: str, db: AsyncSession) -> Analysis:
        """Execute full pipeline."""
        content = await self.acquire(content_id, db)
        prompt = self.prepare(content)
        response = await self.process(prompt, content_id)
        analysis = self.parse(response)
        return await self.render(content_id, analysis, db)

Phase 3: File System as State Machine

Key insight from Karpathy: File existence determines work state.

# Pipeline state management
def get_pipeline_state(work_dir: Path, item_id: str) -> str:
    """Determine pipeline state from file existence."""
    item_dir = work_dir / item_id

    if not item_dir.exists():
        return "pending"
    if not (item_dir / "raw.json").exists():
        return "acquired"
    if not (item_dir / "prepared.txt").exists():
        return "prepared"
    if not (item_dir / "response.json").exists():
        return "processed"
    if not (item_dir / "analysis.json").exists():
        return "parsed"
    return "complete"

def resume_pipeline(work_dir: Path, item_id: str):
    """Resume from last successful stage."""
    state = get_pipeline_state(work_dir, item_id)

    if state == "pending":
        acquire(item_id)
    if state in ["pending", "acquired"]:
        prepare(item_id)
    if state in ["pending", "acquired", "prepared"]:
        process(item_id)
    if state in ["pending", "acquired", "prepared", "processed"]:
        parse(item_id)

    return load_analysis(item_id)

Benefits:

• Idempotent restarts: Kill and resume anytime
• Debuggable: Inspect intermediate files
• Cost-efficient: Never re-call LLM for completed work
• Parallel-safe: Each item in own directory

Phase 4: Structured Output Design

Disclose parsing intent to the model - models perform better when they know how output will be used.

## Good Prompt (Parsing Disclosed)
Analyze this article and provide structured output.

I will parse this programmatically, so respond with valid JSON matching:
{
  "summary": "2-3 sentences",
  "sentiment": "positive" | "neutral" | "negative",
  "topics": ["string array"],
  "confidence": 0.0-1.0
}

Ensure the JSON is complete and parseable.

## Bad Prompt (Parsing Hidden)
Analyze this article. Give me a summary, sentiment, and topics.

Structured Output Patterns

// Pattern 1: Section markers for complex output
const prompt = `Analyze this document.

Respond in this exact format:
===SUMMARY===
[2-3 sentence summary]
===SENTIMENT===
[positive/neutral/negative]
===TOPICS===
[comma-separated topics]
===END===`;

function parse(response: string) {
  const sections = {
    summary: extractSection(response, "SUMMARY"),
    sentiment: extractSection(response, "SENTIMENT"),
    topics: extractSection(response, "TOPICS").split(",").map(s => s.trim()),
  };
  return sections;
}

// Pattern 2: JSON with schema disclosure
const prompt = `Analyze this content.

Respond with a JSON object. I will parse this with Zod, so ensure it matches:
{
  "summary": string (required, 50-200 chars),
  "sentiment": "positive" | "neutral" | "negative" (required),
  "topics": string[] (required, 1-5 items),
  "confidence": number (required, 0.0-1.0)
}`;

Phase 5: Architectural Reduction

Fewer tools = better performance (Vercel d0 case study)

Principles

1. Start minimal: Only add tools when demonstrably needed
2. Combine operations: One tool that does A+B > two separate tools
3. Remove unused tools: If success rate improves, keep it removed
4. Mask, don't delete: Keep in context but mark unavailable (KV-cache optimization)

// Grey Haven: Minimal tool pattern
const MINIMAL_TOOLS = [
  {
    name: "read_database",
    description: "Query tenant data using Drizzle ORM",
    // Combines: list tables, query table, get schema
  },
  {
    name: "update_record",
    description: "Update a record in the database",
    // Combines: update, insert, upsert operations
  },
];

// NOT: 10 separate CRUD tools

Phase 6: Cost Estimation

Estimate before building, adjust architecture based on scale.

def estimate_pipeline_cost(
    num_items: int,
    avg_input_tokens: int,
    avg_output_tokens: int,
    model: str = "claude-sonnet-4-20250514"
) -> dict:
    """Estimate total cost for pipeline run."""

    # Pricing per million tokens (as of Dec 2025)
    PRICING = {
        "claude-sonnet-4-20250514": {"input": 3.00, "output": 15.00},
        "claude-opus-4-5-20251101": {"input": 15.00, "output": 75.00},
        "claude-haiku-3-5-20241022": {"input": 0.80, "output": 4.00},
    }

    rates = PRICING[model]

    total_input = num_items * avg_input_tokens
    total_output = num_items * avg_output_tokens

    input_cost = (total_input / 1_000_000) * rates["input"]
    output_cost = (total_output / 1_000_000) * rates["output"]

    return {
        "items": num_items,
        "total_input_tokens": total_input,
        "total_output_tokens": total_output,
        "input_cost": f"${input_cost:.2f}",
        "output_cost": f"${output_cost:.2f}",
        "total_cost": f"${input_cost + output_cost:.2f}",
        "cost_per_item": f"${(input_cost + output_cost) / num_items:.4f}",
    }

# Example: Karpathy's HN Time Capsule
estimate_pipeline_cost(
    num_items=128,        # articles
    avg_input_tokens=2000, # article + prompt
    avg_output_tokens=500, # analysis
    model="claude-opus-4-5-20251101"
)
# Result: ~$5-10 total, $0.04-0.08 per article

Agent-Assisted Development Workflow

When building LLM features with Claude Code:

1. Define the Task

"I need to analyze customer support tickets and categorize them
by urgency, topic, and suggested response template."

2. Validate Manually

1. Take one real support ticket
2. Paste into Claude.ai with your prompt
3. Verify the output quality
4. Note token usage for cost estimation

3. Design Pipeline Stages

- Acquire: Query tickets from database (Drizzle)
- Prepare: Format ticket + customer context
- Process: Claude API call with structured output
- Parse: Validate with Zod schema
- Render: Update ticket record, notify agent

4. Implement with File Caching

- Each ticket gets a directory: .cache/tickets/{ticket_id}/
- Stage outputs saved as JSON files
- Pipeline resumes from last successful stage

5. Estimate and Optimize

- 1000 tickets/day × 1500 tokens avg = 1.5M tokens
- Sonnet 4: ~$4.50/day input, ~$22.50/day output
- Consider batching, caching common responses

Anti-Patterns to Avoid

When to Apply This Skill

Use this skill when:

• Building any LLM-powered feature
• Creating data processing pipelines
• Implementing AI agents or assistants
• Designing chat-based interfaces
• Building content generation systems
• Creating analysis/classification pipelines
• Integrating Claude into Grey Haven apps

Critical Reminders

1. Manual prototype first - Always validate with target model before automation
2. Pipeline architecture - Deterministic stages around non-deterministic LLM
3. File system state - Use file existence for pipeline progress
4. Structured outputs - Disclose parsing intent in prompts
5. Minimal tools - Fewer tools = higher success rate
6. Cost estimation - Calculate before building at scale
7. Cache aggressively - Never re-call LLM for completed work
8. Tenant isolation - Include tenant_id in all database queries
9. Error tolerance - Design for graceful degradation
10. Incremental processing - Build resume-friendly pipelines

Template Reference

These patterns integrate with Grey Haven templates:

• cvi-template: TanStack Start + Claude integration
• cvi-backend-template: FastAPI + Anthropic SDK pipelines

Skill Version: 1.0