Investigate Signup Spike

Investigate Signup Spike

Use this skill when investigating abnormal signup volume, user registration spikes, or suspected bot/abuse waves. The user may provide a time window, an alert link, or simply describe what they're seeing.

Before starting, ask the user for:

• Database access method (tool name or connection details)
• App/platform name (for web searches)
• Time window to investigate
• Key table/column names for users, messages, sessions, and referrals (schemas vary — confirm before querying)

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Output

This skill produces two deliverables, both saved as markdown files:

1. Detailed Report (signup_spike_investigation_.md)

A comprehensive investigation covering all phases below. Save to the working directory.

2. One-Page Summary (signup_spike_summary_.md)

A concise, scannable summary (max ~60 lines). Structure it exactly as:

# Signup Spike Summary — 

**Window:**  -  UTC | **Volume:**  signups | **Baseline:** ~/hr | **Spike:** ~x

## What Happened

## Key Numbers
| Metric | Value |
|--------|-------|
| Total signups | |
| Spike vs baseline | |
| Dominant cohort | |
| Onboarding completed | |
| Active users (sent messages) | |
| Suspected multi-accounts | |

## Cohort Breakdown

## Risk Assessment
- **Bot likelihood:**  — 
- **Multi-account abuse:** 
- **Referral-driven:** 

## Hypothesis: Probable Cause

## Recommended Actions

## Full Report
See: `signup_spike_investigation_.md`

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Framing Rules

Follow these rules in BOTH reports:

• Hypothesis language: Use "likely", "suggests", "consistent with", "appears to be". Never state unverified conclusions as fact.
• VPN != fraud: Only flag VPN usage as suspicious when combined with other signals (shared IP + similar names, multi-account patterns).
• Shared IP != same person: Always categorize shared IPs by historical account volume before concluding multi-account abuse. High-traffic VPN exit nodes (20+ total accounts) are likely coincidence.

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Investigation Phases

Run phases in order. Each phase informs the next. Parallelize queries within a phase when possible.

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Phase 1: Establish the Spike

Goal: Confirm the spike, measure magnitude, find the inflection point.

Data to retrieve:

• Total signup count within the investigation window
• Hourly signup volume over the past 24h to establish a baseline
• Per-minute signup rate within the window to pinpoint the inflection point

Record: spike magnitude (Nx baseline), exact start time, sustained rate (signups/min).

---

Phase 2: Demographics

Goal: Identify geographic concentration, VPN patterns, onboarding completion, profile quality.

Data to retrieve (run in parallel):

• Signup count grouped by country
• Signup count grouped by timezone
• Country x timezone cross-tab — mismatches (e.g., country=DE, timezone=Asia/Tehran) indicate VPN usage
• Signup count grouped by onboarding status
• Signup count grouped by email domain

If a dominant cohort emerges: run a 24h hourly breakdown filtered to that cohort alongside total signups to see when it started diverging from baseline.

For users with null country/timezone (abandoned onboarding): estimate origin using name script patterns (Unicode ranges for Devanagari, Arabic/Persian, Cyrillic, Latin, etc.). Label these as heuristic estimates in the report.

VPN detection logic: country is typically sourced from IP geolocation; timezone comes from the browser/OS. A mismatch between the two suggests the user's real location differs from their IP.

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Phase 3: Referral Analysis

Goal: Determine whether the spike is organic or referral-chain driven. Skip if your platform has no referral system.

Data to retrieve:

• Top referrers by number of referred signups within the window
• Referral vs organic breakdown (referred_by null vs not null)

Key indicators:

• High referral count = someone is actively incentivizing signups (referral chain or coordinated invite spam)
• Low referral count = externally driven (social media post, viral content, third-party listing)

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Phase 4: Usage Patterns — Bot or Human?

Goal: Classify users as bots, sign-and-abandon accounts, or genuine users.

Data to retrieve (run in parallel):

• Count of users who sent at least one message vs total signups
• Top users by message/session count
• Sample of 30-50 recent messages from new users — eyeball for repetitive, templated, or gibberish content
• Message script/language distribution (especially for users with null country/timezone)

Bot Indicator Checklist:

| Signal | Bot | Human | |--------|-----|-------| | Message content | Repetitive, templated, gibberish | Diverse topics, multilingual | | Sessions per user | 1 session | Multiple sessions, different topics | | Onboarding | Rarely completes | 50%+ complete | | Language diversity | Single script | Multiple scripts | | Content quality | Generic, copy-pasted | Contextual, specific questions |

Look specifically for copy-pasted prompts that appear across many users — a strong signal of tutorial-driven or coordinated activity.

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Phase 5: Multi-Account Detection

Goal: Identify users running multiple accounts.

Assumes you have a way to map users to IPs, and IP metadata (org, fraud score, network type) from an IP intelligence provider.

Data to retrieve — run sequentially:

1. Shared IP overview: Count of IP addresses shared by 2+ new users, and total affected users
2. Cluster detail: For each shared IP, retrieve user count, names, emails, IP metadata (org, country, fraud score, network type)
3. Historical IP volume: For each shared IP, count total accounts ever seen — used to distinguish real multi-accounts from shared VPN exit nodes
4. Name duplicates: Users with identical (normalized) names who signed up in the window
5. Cluster size distribution: How many pairs, triples, quads+ exist

Classify each shared IP by historical volume:

• 1-5 total accounts ever: high confidence same person
• 6-20 total accounts: uncertain, needs additional signal
• 20+ total accounts: likely shared VPN node, probably coincidence

Multi-account signal strength (strongest to weakest):

1. Same name variant + same IP — definite
2. Same email stem + same IP — definite
3. Residential ISP IP, site:twitter.com OR site:x.com `
4. telegram
5. site:youtube.com
6. "" signup invite

Region-specific search tips:

• Persian/Iranian: Search Aparat (site:aparat.com), Virgool (site:virgool.io), use Persian keywords like کسب درآمد (earn money), رایگان (free). Persian Telegram channels are NOT web-indexed — recommend manual search.
• Indian: Search YouTube, use Hindi keywords
• Brazilian: Search YouTube, use Portuguese keywords
• Nigerian: Search Twitter/X, YouTube

Also check:

• Your app's official social accounts for recent posts
• Your blog/changelog for recent announcements (new features, promotions, partnerships)

State findings as hypotheses. If no definitive source is found, say so and list the most probable candidates.

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Phase 7: Write Reports

Produce both deliverables.

Detailed Report Structure (signup_spike_investigation_.md)

1. Executive Summary — 2-3 sentences: spike magnitude, probable cause (as hypothesis), bot verdict
2. Timeline and Volume — hourly/minute breakdown tables, baseline comparison, inflection point
3. User Demographics — geography tables, VPN mismatch analysis, onboarding funnel, name-based estimation (clearly labeled as estimates)
4. Referral Analysis — referral vs organic breakdown, top referrers if applicable
5. Usage Patterns — activity metrics, message content samples, language distribution, bot assessment checklist
6. Multi-Account Analysis — shared IP overview, confidence tiers, definite cases table, cluster size distribution, estimated multi-account rate
7. Source Attribution — web search findings, probable trigger hypothesis, what could not be found
8. Recommendations — monitoring, abuse prevention, product, growth (4-5 bullets each)

One-Page Summary

Follow the template from the Output section. Keep it under 60 lines. Link to the detailed report at the bottom.

Save both files to the working directory and inform the user of both file paths.

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Tips and Gotchas

• Confirm schema first: Table and column names vary significantly across platforms. Always ask or verify before querying — common variations include registered_at vs created_at, display_name vs name, updated_at vs modified_at.
• Parallelize aggressively: Within each phase, most data retrieval tasks are independent. Run them in parallel to save time.
• Read replica lag: If querying a read replica, data may be slightly behind. Account for this with very recent signups.
• Large joins may timeout: Break complex joins into smaller sequential queries if needed.
• IP data location: IP-to-user mapping and IP metadata are often in separate tables. Confirm structure before Phase 5.
• Onboarding nulls: Users who abandoned onboarding mid-flow will have null country/timezone. Use message content and name scripts to estimate origin.
• Rate limits: Log/search tools often have rate limits. If blocked, wait and retry or note the gap in the report.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: theultimateshyam
• Source: theultimateshyam/claude-skills
• License: MIT

Install and usage instructions live in the source repository linked above.