PostHog

What it is and why

PostHog is all-in-one product analytics for apps and SaaS: funnels, retention, user paths, session replay, feature flags and A/B tests in a single tool. Open-source, and you can self-host it. Reach for it when you have a product or app and need to understand user behaviour and ship features behind flags — not just "site visitors", but what people actually do inside.

How to set it up (step by step)

1. Hosting: PostHog Cloud (a generous free event allowance) or self-host (open-source — full control over your data, but it needs resources).
2. Install the SDK for your platform (JS for web, mobile and server SDKs) and initialise it with your project key.
3. Send events. Autocapture of clicks and pageviews plus custom ones: posthog.capture("signed_up"), posthog.capture("purchased", {plan}).
4. Identify users — tie events to a user (posthog.identify(userId)) so retention and paths work.
5. Funnels. Build landing → signup → activation → paid and see where people drop off.
6. Retention — the retention table: do people come back after a day, after a week?
7. Session Replay — watch session recordings to see where users got stuck (like a session recorder, but aimed at the product).
8. Feature flags and A/B. Roll a feature out to 10% → measure the effect → ship it to everyone. Flags are managed from the dashboard.

Ready-made recipe

A product growth loop: the SDK sends events from the app → the funnel shows that only 30% of signups reach the "key action" (activation) → Session Replay shows where newcomers get lost in onboarding → you launch a new onboarding behind a feature flag for 50% of users (A/B) → the retention table confirms the new variant holds people better → you roll it out to 100%. Analytics + experiments + replay in one place, a closed loop of product improvement.

What it costs (honestly)

How it works: a generous free monthly allowance of events/replays/flags on Cloud — enough to get started and for small products. Beyond that you pay by volume (events, session recordings). Self-host is free — you pay for infrastructure, and for PostHog that is not trivial. Check exact limits and prices with PostHog, they change.

When it fits / when it doesn't

• Fits: you have a product/app/SaaS; you need product analytics (funnels/retention/paths); you want session replay + feature flags + A/B in one tool; you value open-source and self-hosting.
• Doesn't fit: a plain site or landing page only (overkill — use a basic web analytics tool); you need maximum simplicity as a beginner; you have no resources to self-host (take Cloud) and do not want to pay by volume.

Risks and responsibility

152-FZ: PostHog collects behavioural data and (once you call identify) ties it to a user → you need consent to process personal data and a privacy policy; session replay must mask sensitive fields (passwords, payment forms — this is configurable). Self-host means infrastructure, security and backups are on you (a plus for data localisation). Cloud means the data sits on PostHog's servers — check the geography. See the section disclaimer.

🤖 Prompt helper

You are a product analyst working with PostHog. The product is "{what: SaaS/app}", the key user action is "{which}". Help me: (1) decide which events and properties to track (a list of capture calls) for my funnel; (2) build an activation funnel and retention view — and what to read in them; (3) use session replay and feature flags to test onboarding hypotheses; (4) set up what 152-FZ requires (consent, masking in replay). Step by step.