Polar

What we tell an AI agent working on a project that uses Polar —2 rules, 2 learned the hard way.

Build a rootnote set for a Polar project Plain text

Polar publishes its own file for agents — docs.polar.sh/llms.txt. That is what the tool is and where its documentation lives. This page is the other half: where it catches agents out. Why both.

Polar for payments

Check a merchant of record's acceptable-use policy against what the product does, before building

Hard-won · Leon Mallett (captivated.online) with Claude Code · reviewed 2026-10-19

Read the restricted-categories list before any integration work, and judge it against what the product actually does — not against what kind of company you are.
Legitimate software was rejected or banned here more than once after integration had started: automated social posting, AI-generated video, and a directory carrying advertising each fell foul of a policy written with something else in mind. Weeks of work were lost each time.
Where anything is close, ask the provider in writing first. An approval given at onboarding is not the same as one given for the feature that ships.

Polar's sandbox does not enforce the eligibility gate, and its signatures deviate from the spec they cite

Hard-won · Leon Mallett (captivated.online) with Claude Code · reviewed 2026-10-15

Three things cost real time here, and none is in the documentation:

An eligibility gate the sandbox does not enforce. Flows that pass in sandbox fail in production, so sandbox success is not evidence.
A signature scheme that deviates from the spec it cites. Implementing the referenced standard faithfully produces rejected webhooks.
Webhook orderings that zero out an active subscription if handlers assume arrival order.

Treat sandbox agreement as a necessary condition and never a sufficient one, and make handlers order-independent rather than ordering-tolerant.

Full account: Wiring Polar billing and webhooks without cutting off paying customers

Polar for licensing

Also applies to every licensing choice, so it is not repeated here:

Revoke a licence when what was paid for ends, never when the customer cancels
A licence check must never lock out somebody who paid

All of it is included when you build a set.

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