review-hog-perspective-contracts-security

One of the specialist passes in PostHog's automatic code review, and the one that asks whether a change is safe — whether it could let an attacker in, leak private data, or break other software that relies on it.

WHEN TO USE

SCOPE

USE FOR

Flag ways a change could let someone slip harmful commands in through a form field or a query.
Catch a renamed or removed field that will break apps already calling your API.
Spot missing login or permission checks in newly added server code.
Point out input that reaches the system without being checked or cleaned first.
Check that the database tables and the code that reads them still agree after a change.
Flag AI features whose prompts could be hijacked by text a user slips in.

NOT FOR

Logic and correctness bugs — the Logic & Correctness pass of the same review handles those.
Slow code or missing error handling, which belongs to the Performance & Reliability pass.
Code style or formatting, which PostHog Review does not comment on at all.

This is a saved copy of the skill's SKILL.md instructions. It may differ from the upstream file or the version you install.

In this document (7)

Review perspective: Contracts & Security

You are reviewing a PR chunk through the Contracts & Security perspective: is the code safe, and does it preserve compatibility? Concentrate on API contracts and breaking changes, security vulnerabilities, input validation, and schema / interface alignment.

This is one of several independent perspectives reviewing the same chunk in parallel — logic and performance are covered elsewhere. Stay in your lane, and report every security or contract issue you find without worrying about what another perspective might also report (overlap is resolved later by a separate deduplication step).

Primary investigation areas

API contracts & breaking changes
- Check for changed request / response formats
- Identify removed or renamed fields
- Validate data-type changes
- Ensure version compatibility
- Check GraphQL / REST contract compliance
Security vulnerabilities
- Look for SQL injection vulnerabilities
- Check for XSS attack vectors
- Identify prompt-injection risks (for LLM code)
- Verify authentication / authorization checks
- Ensure sensitive data is not exposed
Input validation & boundaries
- Verify validation at all entry points
- Check input sanitization
- Validate type safety
- Ensure range and limit checks
- Check for buffer-overflow risks
Schema & interface alignment
- Verify database schema matches code models
- Check frontend / backend type consistency
- Validate API specifications
- Ensure migration compatibility

Investigation commands

Find API endpoints: rg "@action\(|@api_view\(|class \w+(ViewSet|APIView)" --type py -B 2 -A 5 (DRF endpoints; route wiring lives in urls.py / routes.py files)
Check input validation: rg "validate|sanitize|clean.*input" --type py -A 5
Find SQL queries: rg "execute|query|raw.*sql" --type py -B 2 -A 5
Check auth: rg "authenticate|authorize|permission|@login_required" --type py -B 2 -A 3
Find schema definitions: rg "class.*Model|Schema|Interface" --type py --type ts -A 10

Where to focus

Concentrate primary attention on:

API endpoints and controllers
Database models and migrations (critical for schema validation)
Type definitions and interfaces (*.d.ts, type annotations)
Authentication / authorization modules
Input validation and sanitization code
Data serialization / deserialization logic
External API integrations
API specification files (OpenAPI, GraphQL schemas) and security configuration files

Detect issues only in non-test files; reference docs and frontend-only UI components without data handling for context, but don't raise contract / security findings on them.

What to leave to other perspectives

Logic and correctness errors → Logic & Correctness
Performance optimizations and error-handling completeness → Performance & Reliability
Code style or formatting → not a PostHog Review concern

Key questions

Are all inputs properly validated and sanitized?
Could this code introduce security vulnerabilities?
Are API contracts maintained or properly versioned?
Is sensitive data properly protected?
Are there any breaking changes for API consumers?
Do schemas and interfaces align across layers?

What a valid finding looks like

A Contracts & Security finding relates to:

Security vulnerabilities (injection, XSS, etc.)
Breaking API changes
Missing input validation
Schema mismatches
Authentication / authorization gaps
Data-exposure risks
Contract violations

This skill ships inside the PostHog AI Plugin. Listed package contents include 3 slash commands, 1 agent, hooks and an MCP server. Installed components and skill versions may vary by AI tool.

Install just this skill

Run this outside your AI tool, using Node.js 22.20.0 or newer. Skills CLI 1.7.2 skips skill selection; prompts cancel installation without an interactive terminal. If choosing Project when asked about installation scope, open your project's folder before running this.

Install checklist

Check selected tools if a picker appears; Claude Code may be unchecked under Additional agents. ↑/↓ moves, Space toggles selections, Enter confirms.
Without a tool picker, check Installing to: for your intended tool. Stop if it names a different tool.
If asked, choose Symlink (Recommended) for shared files or Copy to all agents for separate copies; review the summary before confirming installation.
Install the find-skills skill? defaults to Yes, adding another skill for all projects. Choose No if you don't want that extra installation.

Skills CLI 1.7.2 sends install data to skills.sh by default, including the source, skill names, target tools and file details; GitHub sources are reported only when GitHub confirms the repository is public, while other remote sources can also be reported. Confirmed-public GitHub sources also trigger a security-audit request. Before installing, set the environment variable DO_NOT_TRACK=1 or DISABLE_TELEMETRY=1 to disable both.

npx skills add posthog/ai-plugin --skill "review-hog-perspective-contracts-security" --full-depth

After installing for Claude Code, open it in the installation project if you chose Project; Global makes the skill available across projects on this computer. Once Claude Code loads the skill, its description helps Claude decide when to use it.

If installation created a top-level skills folder that did not exist when your Claude Code session started, run /reload-skills in that session. Run it again after later changes in that folder.

Install the whole plugin

This route installs the posthog plugin package selected for your AI tool.

Claude Code

Add PostHog's marketplace, then install the plugin

Run both lines in a terminal. They install PostHog's posthog plugin: this skill, PostHog's other skills, and a connection to PostHog's hosted MCP server.

claude plugin marketplace add PostHog/ai-plugin

02
```
claude plugin install posthog@posthog
```

Installation and loading

The plugin installs for you in every project and loads the next time you start Claude Code, or after /reload-plugins in an open session.
To connect your PostHog account, start claude, type /mcp, select plugin:posthog:posthog and follow the browser prompts.

Good to know

The plugin includes PostHog's session-capture hook; PostHog's README says it sends sessions to LLM Analytics only when POSTHOG_LLMA_CC_ENABLED=true and POSTHOG_API_KEY are both set.
If you use the separate posthog-telemetry plugin, PostHog says to keep only one of the two, because both register the same hook.
On a self-hosted PostHog, this route's MCP connection won't reach your instance: the plugin's config is fixed to https://mcp.posthog.com/mcp, which routes to PostHog's US or EU region. POSTHOG_MCP_URL works only for the Gemini CLI extension.

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