Chapter 18: Perplexity Cost Optimization

Purpose: Reduce Perplexity MCP costs by 80%+ using cache-first pattern Prerequisites: Perplexity MCP configured, Basic Memory MCP installed Time to Implement: 15 minutes ROI: $0.005 per cached query (80%+ budget savings on repeat topics)

The Problem

Perplexity MCP charges $0.005 per query (~$5/month budget). Without caching:

Same research topics are searched repeatedly
Budget depletes quickly on common queries
No institutional memory of research results

The Solution: Cache-First Pattern

Before ANY Perplexity search:

Check Memory MCP cache first (mcp__basic-memory__search_notes("topic"))
If found → Use cached result (FREE!)
If not found → Use Perplexity, then IMMEDIATELY cache results

Setup

1. Configure Both MCPs

In .mcp.json or .claude/mcp_servers.json:

{
  "mcpServers": {
    "perplexity": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "perplexity-mcp"],
      "env": {
        "PERPLEXITY_API_KEY": "${PERPLEXITY_API_KEY}"
      }
    },
    "basic-memory": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@anthropics/mcp-server-basic-memory"],
      "env": {
        "MEMORY_PATH": "~/basic-memory"
      }
    }
  }
}

2. Create Research Cache Folder

The cache should be global (available across all projects):

mkdir -p ~/basic-memory/research-cache

3. Add Cache-First Rule to CLAUDE.md

Add this to your project’s CLAUDE.md Critical Rules section:

### Perplexity Cache-First Rule
PATTERN: "ALWAYS check Memory MCP before Perplexity"
BEFORE_SEARCH: "mcp__basic-memory__search_notes('topic')"
IF_FOUND: "Use cached result (FREE!)"
IF_NOT_FOUND: "Use Perplexity, then cache with mcp__basic-memory__write_note(folder='research-cache')"
ROI: "$0.005 per cached query, 80%+ savings"

The Workflow

Step 1: Check Cache First

# Before any Perplexity search
mcp__basic-memory__search_notes("topic keywords")

If results found → STOP! Use the cached result.

Step 2: Only Then Use Perplexity

# Only if cache miss
mcp__perplexity__search(query="your research question")

Step 3: Immediately Cache Results

# RIGHT AFTER every Perplexity search
mcp__basic-memory__write_note(
    title="Topic Keywords Summary",
    content="""# Research: [Topic]
**Source**: Perplexity search
**Date**: [Today's date]
**Query**: [What you searched for]

## Key Findings
- Finding 1
- Finding 2
- Finding 3

## Sources
- [List sources from Perplexity response]
""",
    folder="research-cache"
)

Naming Convention for Cache Notes

Use descriptive, searchable titles:

Topic	Cache Title
React 19 features	`react-19-features-2025`
Claude Code hooks	`claude-code-hooks-guide`
PostgreSQL optimization	`postgresql-query-optimization`
Node.js best practices	`nodejs-best-practices-2025`

Cost Analysis

Without Caching

| Searches/Month | Cost | |—————-|——| | 100 | $0.50 | | 500 | $2.50 | | 1000 | $5.00 |

With Cache-First (80% hit rate)

| Searches/Month | Actual Queries | Cost | |—————-|—————-|——| | 100 | 20 | $0.10 | | 500 | 100 | $0.50 | | 1000 | 200 | $1.00 |

Savings: 80% cost reduction

Example: Research Cache in Action

Scenario: You need to look up “Claude Code hooks” for the 5th time this month.

Without caching (old way):

User: "How do Claude Code hooks work?"
Claude: [Uses Perplexity] → $0.005
...(next week)...
User: "What hook types are available?"
Claude: [Uses Perplexity again] → $0.005

Cost: $0.01+ and growing

With caching (new way):

User: "How do Claude Code hooks work?"
Claude: [Checks cache] → Found 'claude-code-hooks-guide' → FREE!
...(next week)...
User: "What hook types are available?"
Claude: [Checks same cache] → Same note → FREE!

Cost: $0.005 (one-time) + $0.00 (all future)

Validation Checklist

Perplexity MCP configured and working
Basic Memory MCP configured and working
research-cache/ folder created
Cache-first rule added to CLAUDE.md
Test: Cache miss → Perplexity → Cache write
Test: Cache hit → No Perplexity call

MCP Integration Guide - Setting up MCPs
Memory Bank Hierarchy - Knowledge organization
perplexity-cache-skill - Executable workflow

Evidence

Source Project: Production production system Validation: research-cache/ folder with 10+ cached results Pattern: Documented in CLAUDE.md as mandatory rule Enforcement: PostToolUse hook reminder after every Perplexity call

Cost Optimization Authority: Proven pattern for 80%+ Perplexity cost reduction Usage: Implement on any project using Perplexity MCP Created: December 2025