Development Diary - January 18, 2026

📋Daily Summary

Today was a landmark day for ToonNotes developer tooling. I built and deployed a complete GA4 Analytics MCP Server that provides 23 tools for querying Google Analytics 4 data programmatically. This enables Claude Code to pull real analytics data during development sessions, making the /analytics-insight skill dramatically more useful.

The MCP server covers four categories of GA4 functionality:

Query Tools: Run custom reports, get active users, top events, user metrics
Real-time Tools: Live user counts, recent events, currently viewed pages
Admin Tools: Manage custom dimensions, key events, audiences
Export Tools: Batch reports, CSV export, summary reports

The biggest challenge was authentication. Google Service Account JWT authentication required careful handling, and I spent significant time debugging a subtle issue where environment variables had trailing newlines (\n) that broke the JWT signing process.

🕐Work Sessions

Session 1: Android IAP Support

Fixed Android in-app purchase configuration and pricing across multiple currencies.

Session 2: Health Check Cron

Implemented automated health checks with cron job scheduling.

Session 3-4: GA4 Implementation Planning

Researched GA4 API capabilities and planned the MCP server architecture with three API layers (Data, Realtime, Admin).

Session 5-7: MCP Server Core Implementation

Built the complete MCP server with:

Google Service Account JWT authentication (src/auth/google.ts)
GA4 Data API client for reports (src/api/data.ts)
GA4 Realtime API for live monitoring (src/api/realtime.ts)
GA4 Admin API for configuration (src/api/admin.ts)
23 MCP tools across query, realtime, admin, and export categories

Session 8-9: Authentication Debugging

Spent considerable time debugging "invalid_grant: account not found" error:

First thought: Service account not added to GA4 → User added it → Still failed
Second thought: APIs not enabled → User enabled them → Still failed
Created debug endpoint to inspect env vars → Found trailing \n in values
Fixed using printf '%s' instead of heredoc for env var injection

Session 10: Bug Fixes & Validation

Fixed GA4 batch limit (max 5 requests, had 6)
Added defensive null handling for parseReportToRecords
Tested all 23 tools successfully with real GA4 data

Session 11: Skill Update & Documentation

Updated /analytics-insight skill to use MCP server with:

MCP tools quick reference table
Example usage patterns
Server configuration documentation

🏷️Categorized Work

Implementation (8 commits)

Complete MCP server package with 23 GA4 tools
JWT authentication with Google Service Account
Data, Realtime, and Admin API clients
Batch reporting and CSV export functionality

Infrastructure (2 commits)

Vercel deployment configuration
Environment variable setup (GA4_PROPERTY_ID, GOOGLE_SERVICE_ACCOUNT_EMAIL, GOOGLE_SERVICE_ACCOUNT_KEY)

Bug Fixes (1 commit)

Fixed batch request limit (5 max)
Added defensive handling for undefined headers in report parsing

📸Screenshots

No screenshots captured. The MCP server is a backend service without UI.

💡Insights & Learnings

💡

Environment Variable Gotcha

When setting Vercel environment variables via CLI, heredocs add trailing newlines:

# WRONG - adds \n
vercel env add VAR_NAME production <<< "value"

# CORRECT - no trailing newline
printf '%s' "value" | vercel env add VAR_NAME production

💡

GA4 Batch Request Limit

GA4 Data API limits batch requests to 5 per call. The batchRunReports endpoint will reject requests with more, returning a clear error message.

💡

MCP Server Architecture

The mcp-handler package makes creating MCP servers straightforward:

const handler = createMcpHandler(
  (server) => {
    server.tool('tool_name', schema, async (args) => { ... });
  },
  { name: 'server-name', version: '1.0.0' },
  { basePath: '/api' }
);

💡

Google Service Account Authentication

JWT tokens for Google APIs require:

Service account email
Base64-decoded private key
Correct scope (https://www.googleapis.com/auth/analytics.readonly)
Token cached for ~55 minutes (1-hour expiry minus buffer)

📊Statistics

🕐

Sessions

📝

Commits

📁

50+

Files Changed

➕

23,895

Lines Added

➖

2,349

Lines Deleted

🏷️

Implementation

Primary Category

🎯Tomorrow's Focus

Test Analytics Insight Skill - Run /analytics-insight weekly to validate the full workflow
Add More Report Types - Consider adding funnel analysis and cohort reports
Documentation - Write usage guide for the MCP server

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