# AGENTS.md — Build guide for WooCommerce Subscriptions ## Project scope Build a small recurring-billing service for one product using hosted Stripe Checkout and verified billing events. Expose a server-side entitlement check and an operator reconciliation view; this is not a WordPress plugin clone. Catalogue verdict: kinda. The actual hard part of recurring billing lives at the payment processor, not in this plugin: Stripe Billing already does tokenization, renewal attempts, SCA, proration and dunning. So an agent can absolutely wire a small self-hosted checkout plus webhook listener plus entitlement table in a weekend, and for one product with two or three plans that is genuinely enough. What you cannot one-shot is the part that makes this extension worth a license: living inside WooCommerce so that orders, coupons, taxes, shipping, emails, reports and forty other plugins all understand a subscription. If you already run a real Woo store, replacing this means rebuilding the glue, not the billing. If you just want money to arrive monthly for something you built, you never needed WordPress in the first place. Use the implementation prompt below to define the deliverable. Complete each phase's acceptance checks before extending the scope. ## Working agreement - Inspect the repository and its existing instructions before choosing paths, dependencies or commands. Keep one coherent stack and explain changes to the proposed architecture. - Plan a vertical slice that accepts a real input and produces the useful output described below. Persist only the state the prompt calls for; respect memory-only and upstream-managed workflows. Use fixtures only when they are clearly labelled. - After scaffolding, document the actual install, development, check and build commands in README and keep them synchronized with the package or project manifest. Do not report commands as successful unless they ran. - Work in small steps. At handoff, list implemented flows, checks actually performed, remaining blockers, and any credentials or provider setup the owner must supply. - Do not publish, spend money, contact customers, delete source data or run irreversible migrations without the project owner's authorization. ## Prerequisites - Node, persistent SQLite, a configured Stripe account and webhook secret, public HTTPS callbacks and authenticated customer/owner sessions. Check tax/payment requirements separately. - Implementation components: Node.js, TypeScript and Express with server-rendered HTML and small browser modules. SQLite through better-sqlite3 with migrations, prepared statements and a single background worker. Stripe Checkout/Billing Portal, verified raw-body webhooks and a supported session/magic-link authentication library. - Scope boundary: Tax advice, multiple payment processors and WooCommerce compatibility are outside scope. ## Stack and architecture - Node.js, TypeScript and Express with server-rendered HTML and small browser modules. - SQLite through better-sqlite3 with migrations, prepared statements and a single background worker. - Stripe Checkout/Billing Portal, verified raw-body webhooks and a supported session/magic-link authentication library. - Domain model: hardcoded product plans, Stripe customer/session IDs, subscription snapshots, entitlement policies and webhook receipts ## Security and data integrity - Public routes accept only their documented inputs with rate/size limits. Protect every owner/customer action with authenticated authorization and CSRF checks; keep secrets outside exports and redact personal data from logs. - Correctness boundary: Out-of-order events cannot overwrite newer subscription state; access follows a documented paid/trial/grace/cancel policy rather than a return URL. - Use short SQLite transactions and persist job state before starting work. Give retries stable operation IDs; report incomplete or unknown results instead of silently repeating them. - Use a consistent SQLite backup and an attachment manifest. Export portable JSON/CSV, then restore to a new directory without overwriting the original data. ## Agent implementation rules - Project rule — data model: hardcoded product plans, Stripe customer/session IDs, subscription snapshots, entitlement policies and webhook receipts - Project rule — preserve this invariant: Out-of-order events cannot overwrite newer subscription state; access follows a documented paid/trial/grace/cancel policy rather than a return URL. - Project rule — acceptance evidence: Replay and reorder subscription callbacks, then reconcile against Stripe to the same access state; a cancelled entitlement cannot pass the protected endpoint. ## Optional agent skills and references - Optional external skill: [web-design-guidelines](https://github.com/vercel-labs/agent-skills/blob/main/skills/web-design-guidelines/SKILL.md) — Review web interfaces for accessibility, keyboard focus, forms, navigation and interaction quality. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. - Optional external skill: [sharp-edges](https://github.com/trailofbits/skills/blob/main/plugins/sharp-edges/skills/sharp-edges/SKILL.md) — Review security-sensitive APIs and configuration for dangerous defaults and easy-to-misuse interfaces. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. - Optional external skill: [stripe-best-practices](https://github.com/stripe/ai/blob/main/skills/stripe-best-practices/SKILL.md) — Plan Stripe checkout, subscriptions, webhooks, platform payments and secure API integration. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. Read the linked SKILL.md and its dependencies before adding a skill. Select only the skills matching this project's runtime and task; their documentation does not supply API access, credentials or approval to perform external actions. Pin the reviewed revision where the tool supports it. Follow the chosen agent's documented project-level installation mechanism. ## Distribution ideas These are optional planning notes. Obtain the owner's approval before publishing or contacting anyone. - Demonstrate the actual WooCommerce Subscriptions-inspired workflow with owned or clearly labeled sample data: Build a small recurring-billing service for one product using hosted Stripe Checkout and verified billing events. Expose a server-side entitlement check and an operator reconciliation view; this is not a WordPress plugin clone. - Publish a reproducible walkthrough with this observable result: Replay and reorder subscription callbacks, then reconcile against Stripe to the same access state; a cancelled entitlement cannot pass the protected endpoint. - Explain who can operate this scoped tool, its setup and ongoing costs, and these remaining product gaps: Tax advice, multiple payment processors and WooCommerce compatibility are outside scope. Avoid guaranteed savings, performance scores or implied endorsement. ## Engineering roadmap 1. Phase 1 — Scope and fixtures. Implement this bounded workflow: Build a small recurring-billing service for one product using hosted Stripe Checkout and verified billing events. Expose a server-side entitlement check and an operator reconciliation view; this is not a WordPress plugin clone. Record prerequisites, select representative user-owned fixtures and document the unsupported features: Tax advice, multiple payment processors and WooCommerce compatibility are outside scope. 2. Phase 2 — Durable model. Model hardcoded product plans, Stripe customer/session IDs, subscription snapshots, entitlement policies and webhook receipts Add migrations or a versioned document format, explicit validation, stable IDs and a visible import-error report. Preserve this rule: Out-of-order events cannot overwrite newer subscription state; access follows a documented paid/trial/grace/cancel policy rather than a return URL. 3. Phase 3 — Complete the first useful path. Implement the workflow's input, review and output interface, with clear controls and explicit empty/error states. Use short SQLite transactions and persist job state before starting work. Give retries stable operation IDs; report incomplete or unknown results instead of silently repeating them. 4. Phase 4 — Permissions and integration failure. Public routes accept only their documented inputs with rate/size limits. Protect every owner/customer action with authenticated authorization and CSRF checks; keep secrets outside exports and redact personal data from logs. Request integration credentials and permissions only for the enabled feature; show a disconnected state instead of mock results. 5. Phase 5 — Portable handoff. Use a consistent SQLite backup and an attachment manifest. Export portable JSON/CSV, then restore to a new directory without overwriting the original data. Include setup, operating limits, fixture walkthrough and shutdown/restart instructions in the README. 6. Phase 6 — Acceptance scenarios. Replay and reorder subscription callbacks, then reconcile against Stripe to the same access state; a cancelled entitlement cannot pass the protected endpoint. Repeat the workflow after restart and with a denied permission or unavailable dependency; show recoverable failure rather than a success placeholder. ## Paid-product capabilities outside this build - Integration with the WooCommerce order, coupon, tax and shipping machinery, so subscriptions are no longer just orders your other plugins understand - Gateway breadth: you are married to one processor instead of the dozen Woo supports - Customer-facing plan switching, pausing, resubscribing and prorated upgrades in your own UI, unless you accept the hosted portal as-is - Admin reporting, renewal calendars and bulk actions over thousands of subscribers - Years of edge case handling for partial renewals, mixed carts, manual renewals and payment method migrations ## Implementation prompt WORKING SLICE Build a small recurring-billing service for one product using hosted Stripe Checkout and verified billing events. Expose a server-side entitlement check and an operator reconciliation view; this is not a WordPress plugin clone. Build this scoped WooCommerce Subscriptions-inspired workflow with a documented data model and visible failure states. Architecture - Node.js, TypeScript and Express with server-rendered HTML and small browser modules. - SQLite through better-sqlite3 with migrations, prepared statements and a single background worker. - Stripe Checkout/Billing Portal, verified raw-body webhooks and a supported session/magic-link authentication library. Prerequisites and limits Node, persistent SQLite, a configured Stripe account and webhook secret, public HTTPS callbacks and authenticated customer/owner sessions. Check tax/payment requirements separately. Outside this release: Tax advice, multiple payment processors and WooCommerce compatibility are outside scope. Data model and correctness hardcoded product plans, Stripe customer/session IDs, subscription snapshots, entitlement policies and webhook receipts Invariant: Out-of-order events cannot overwrite newer subscription state; access follows a documented paid/trial/grace/cancel policy rather than a return URL. Use short SQLite transactions and persist job state before starting work. Give retries stable operation IDs; report incomplete or unknown results instead of silently repeating them. Security and privacy Public routes accept only their documented inputs with rate/size limits. Protect every owner/customer action with authenticated authorization and CSRF checks; keep secrets outside exports and redact personal data from logs. Recovery and export Use a consistent SQLite backup and an attachment manifest. Export portable JSON/CSV, then restore to a new directory without overwriting the original data. Implementation order 1. Phase 1 — Scope and fixtures. Implement this bounded workflow: Build a small recurring-billing service for one product using hosted Stripe Checkout and verified billing events. Expose a server-side entitlement check and an operator reconciliation view; this is not a WordPress plugin clone. Record prerequisites, select representative user-owned fixtures and document the unsupported features: Tax advice, multiple payment processors and WooCommerce compatibility are outside scope. 2. Phase 2 — Durable model. Model hardcoded product plans, Stripe customer/session IDs, subscription snapshots, entitlement policies and webhook receipts Add migrations or a versioned document format, explicit validation, stable IDs and a visible import-error report. Preserve this rule: Out-of-order events cannot overwrite newer subscription state; access follows a documented paid/trial/grace/cancel policy rather than a return URL. 3. Phase 3 — Complete the first useful path. Implement the workflow's input, review and output interface, with clear controls and explicit empty/error states. Use short SQLite transactions and persist job state before starting work. Give retries stable operation IDs; report incomplete or unknown results instead of silently repeating them. 4. Phase 4 — Permissions and integration failure. Public routes accept only their documented inputs with rate/size limits. Protect every owner/customer action with authenticated authorization and CSRF checks; keep secrets outside exports and redact personal data from logs. Request integration credentials and permissions only for the enabled feature; show a disconnected state instead of mock results. 5. Phase 5 — Portable handoff. Use a consistent SQLite backup and an attachment manifest. Export portable JSON/CSV, then restore to a new directory without overwriting the original data. Include setup, operating limits, fixture walkthrough and shutdown/restart instructions in the README. 6. Phase 6 — Acceptance scenarios. Replay and reorder subscription callbacks, then reconcile against Stripe to the same access state; a cancelled entitlement cannot pass the protected endpoint. Repeat the workflow after restart and with a denied permission or unavailable dependency; show recoverable failure rather than a success placeholder. Acceptance Replay and reorder subscription callbacks, then reconcile against Stripe to the same access state; a cancelled entitlement cannot pass the protected endpoint. Use real source data or clearly labeled fixtures. Explain unsupported input and provider failures; do not fabricate analytics, delivery receipts, accuracy claims or security guarantees. Optional agent guidance Optional external skill: [web-design-guidelines](https://github.com/vercel-labs/agent-skills/blob/main/skills/web-design-guidelines/SKILL.md) — Review web interfaces for accessibility, keyboard focus, forms, navigation and interaction quality. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. Optional external skill: [sharp-edges](https://github.com/trailofbits/skills/blob/main/plugins/sharp-edges/skills/sharp-edges/SKILL.md) — Review security-sensitive APIs and configuration for dangerous defaults and easy-to-misuse interfaces. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. Optional external skill: [stripe-best-practices](https://github.com/stripe/ai/blob/main/skills/stripe-best-practices/SKILL.md) — Plan Stripe checkout, subscriptions, webhooks, platform payments and secure API integration. Review its instructions and compatibility before use; it does not grant deployment, data-access or publication permission. Project rule — data model: hardcoded product plans, Stripe customer/session IDs, subscription snapshots, entitlement policies and webhook receipts Project rule — preserve this invariant: Out-of-order events cannot overwrite newer subscription state; access follows a documented paid/trial/grace/cancel policy rather than a return URL. Project rule — acceptance evidence: Replay and reorder subscription callbacks, then reconcile against Stripe to the same access state; a cancelled entitlement cannot pass the protected endpoint. ## Completion evidence Demonstrate the prompt's acceptance scenarios against the scoped workflow. Include setup from a clean checkout and failure recovery. Check persistence across restart and export/restore only for the state the prompt says to store; for memory-only tools, confirm that temporary content is discarded as specified. Record actual results and remaining limitations. A detailed plan alone does not establish a working replacement.