How to Vibe Code Your Own lemlist Alternative

You are building a production-ready software product named “Sendstep”, a deliberately focused alternative to lemlist. Build a complete, usable vertical slice—not a landing page, static mockup, or disconnected collection of components.

WORKING AGREEMENT
Before writing implementation code, produce a short technical plan that names the routes or pages, server actions or endpoints, data tables, important state transitions, authorization boundaries, background jobs, and external adapters. Resolve contradictions in favor of the narrow audience and non-goals below. Prefer a small, legible architecture over speculative abstraction, but do not omit persistence, validation, error handling, or tests.

PRODUCT BRIEF
Primary user: one seller sending a short email sequence to a personal list.
Primary outcome: upload contacts, send sequenced email, and stop the next step when someone replies.
Product principle: optimize the exact workflow below instead of copying the full breadth of lemlist. A first-time user should understand what to do from the interface itself, without a tour or documentation.

END-TO-END USER JOURNEYS
Implement all of these flows through the real interface and persistent data layer:
1. The owner uploads ten contacts, writes a two-step sequence with a wait of three days, and starts it.
2. Step one sends; a contact replies; the owner marks the reply and step two is skipped for that contact.
3. The owner pauses the sequence, and contacts still waiting do not receive the next email.

SCREENS AND INFORMATION ARCHITECTURE
Build these as coherent responsive views. Each screen must specify its primary action, secondary actions, visible status, validation feedback, empty state, loading or pending state, success confirmation, and recoverable failure state.
1. Sequence editor: ordered steps, wait days, subject, body with first-name token, and start or pause.
2. Contacts: CSV import preview, status (queued, sent, replied, bounced), and search.
3. Outbox: each send, accepted or failed, time, and a retry that skips replied rows.
4. Reply inbox: the incoming message, mark-replied action, and the contact status after save.

CORE CAPABILITIES
1. a sequence with ordered steps, wait days, subject, and body tokens
2. CSV contact import with a preview and row errors
3. queued, sent, replied, and bounced states per contact
4. a send log with retry that skips replied and bounced rows
5. a reply inbox that marks the contact and cancels later steps

DETAILED BEHAVIOR AND BUSINESS RULES
Treat these as server-enforced product requirements, not interface suggestions:
1. Send only to contacts still queued for that step, and skip any contact marked replied, paused, or bounced.
2. Create one send log row per contact and step; a retry of an already-sent step does not email again.
3. Honor pause immediately so a worker that wakes after pause does not send.
4. Rate-limit sends, keep provider credentials off the client, and store unsubscribe or bounce as a terminal state.

DATA MODEL AND LIFECYCLE
Design a small relational schema centered on Sequence, Step, Contact, SendAttempt, Reply. Before implementing it, document:
1. Each table’s purpose, primary key, ownership or tenant boundary, timestamps, status fields, and important attributes.
2. Foreign keys, uniqueness constraints, check constraints, indexes needed by the named screens, and transaction boundaries for multi-record changes.
3. The allowed lifecycle or state transitions, who may trigger each transition, which transitions are terminal or reversible, and what audit history must remain immutable.
4. Archive, retention, and deletion behavior, including what happens to dependent records and external files.
5. Idempotency strategy for submissions, jobs, imports, notifications, webhooks, or retries where applicable.
Use migrations rather than ad-hoc schema creation. Store time instants consistently and retain named timezone context whenever local schedules or dates matter. Never rely on a counter, disabled button, or client-side check to preserve a business invariant.

USERS, AUTHENTICATION, AND PERMISSIONS
Implement only the roles required by the stated audience. Make the ownership and visibility model explicit before coding. Enforce authorization in every server-side query and mutation, including search, exports, attachments, live updates, and guessed URLs—not merely by hiding controls. Use secure session defaults, protect state-changing requests, and provide an understandable signed-out, expired-session, and forbidden state. Seed distinct users when multiple roles are required so permissions can be demonstrated and tested.

INTERACTION AND VISUAL DIRECTION
The product should feel fast, calm, focused, and credible rather than like a generic admin template. Use a clear visual hierarchy, restrained color, readable typography, generous hit targets, and consistent placement for primary actions. Start with server-rendered HTML and progressively enhance only the interactions that benefit from it. The core workflow must remain understandable if enhancement fails.

Start with server-rendered Astro pages and ordinary HTML forms on Node.js. Add client JavaScript only for interactions that need browser state, browser APIs, drag-and-drop, or live updates. The core workflow must remain understandable if client JavaScript fails.

Design mobile layouts intentionally instead of simply stacking desktop panels. Support keyboard navigation, visible focus, semantic landmarks, explicit labels, useful page titles, reduced-motion preferences, and screen-reader announcements for asynchronous results. Never use color alone to communicate state. Destructive actions require clear scope and confirmation; safe repeated actions should be idempotent.

TECHNICAL DIRECTION
Build this version with Node.js and Astro. Use Astro for routing, layouts, and server-rendered pages. Start with ordinary HTML forms. Add client JavaScript only when the interface needs it. Prefer Cloudflare D1 for relational persistence, R2 for object storage, Workers for server endpoints and scheduled work, Durable Objects only for coordinated real-time state, and Workflows or Queues for durable background jobs—but only when the product requirements call for them.

Keep domain rules in testable server-side modules instead of route handlers or UI components. Separate persistence, external providers, and background work behind small interfaces without building a framework. Prefer ordinary HTML forms and URLs for durable navigation; use optimistic interaction only when failure can be reconciled clearly.

The product brief currently identifies Astro, Workers, D1 as capability context. Preserve any required native, browser-only, edge, storage, real-time, or background-processing capability through a narrow adapter appropriate to the selected framework. If the core workflow genuinely requires native or browser APIs, keep that runtime as the primary execution surface rather than simulating inaccessible capabilities or inventing an unnecessary web surface.

Integrate with transactional email and Cloudflare Cron Triggers. For every integration:
- List required environment variables in an .env.example without real secrets.
- Add a small adapter with timeouts, normalized errors, and a deterministic local fake or development path.
- Verify inbound signatures and deduplicate provider events where supported.
- Keep credentials server-side, encrypt long-lived provider tokens at rest, and redact secrets and sensitive payloads from logs.
- Define retry, backoff, and idempotency behavior for any side effect that can be repeated.

SECURITY AND PRIVACY
Send only to contacts still queued for that step, honor pause and replied states in the worker, and keep provider credentials off the client.
Validate, normalize, and length-limit all untrusted input on the server. Escape rendered content by default, sanitize any intentionally accepted markup, rate-limit public or abuse-prone actions, and use private object storage plus short-lived authorized URLs for sensitive files. Collect the minimum personal data necessary for the named workflow. Document retention and deletion behavior. Add specific protections for the riskier surfaces in this app, such as uploads, redirects, outbound requests, email delivery, OAuth, webhooks, CSV import or export, and real-time connections.

ACCEPTANCE SCENARIOS
Automate these app-specific scenarios at the most appropriate level:
1. A contact marked replied after step one never receives step two.
2. Starting an already-running sequence does not duplicate queued sends.
3. An invalid CSV row is reported and no contacts from that file are saved.

TESTING
Add focused unit tests for state transitions, authorization predicates, normalization, date or money calculations, and other risky domain rules. Add integration tests for persistence constraints and each external adapter’s success, timeout, retry, and rejection paths. Add at least one browser-level test for every end-to-end journey above, including one small-screen viewport. Tests must use isolated data and run through a documented single command.

OPERATIONS AND FAILURE RECOVERY
Add structured server logs with request, job, or event correlation IDs but no secrets or unnecessarily sensitive data. Make failures actionable in both the interface and logs. Background work must expose pending, succeeded, failed, and retrying states where relevant; do not silently swallow errors. Include safe database migration and rollback guidance, seed data, backup and restore notes, external-data cleanup behavior, and a basic health or diagnostic path appropriate to the stack.

DELIVERABLES
Ship the working application, migrations, representative seed data, tests, .env.example, and a concise README. The README must cover prerequisites, local setup, environment variables, migrations, seed and test commands, deployment, integration setup, backup and restore, security decisions, and known limitations. Seed data should exercise the happy path plus at least one empty, failed, overdue, expired, archived, or permission-restricted state relevant to the product.

DEFINITION OF DONE
The app is complete when a fresh developer can follow the README, create and migrate the database, run the app, sign in as each relevant role, complete every named journey using real persisted data, refresh without losing state, recover from common failures, and use the core interface on phone and desktop. All acceptance scenarios pass, permission boundaries are covered by tests, and no core screen is left as a placeholder.

NON-GOALS
Do not build a lead database, LinkedIn automation, or a dialer. Hunter already covers saved email patterns. Mailchimp already covers a broadcast to a list.

You are building a production-ready software product named “Sendstep”, a deliberately focused alternative to lemlist. Build a complete, usable vertical slice—not a landing page, static mockup, or disconnected collection of components.

WORKING AGREEMENT
Before writing implementation code, produce a short technical plan that names the routes or pages, server actions or endpoints, data tables, important state transitions, authorization boundaries, background jobs, and external adapters. Resolve contradictions in favor of the narrow audience and non-goals below. Prefer a small, legible architecture over speculative abstraction, but do not omit persistence, validation, error handling, or tests.

PRODUCT BRIEF
Primary user: one seller sending a short email sequence to a personal list.
Primary outcome: upload contacts, send sequenced email, and stop the next step when someone replies.
Product principle: optimize the exact workflow below instead of copying the full breadth of lemlist. A first-time user should understand what to do from the interface itself, without a tour or documentation.

END-TO-END USER JOURNEYS
Implement all of these flows through the real interface and persistent data layer:
1. The owner uploads ten contacts, writes a two-step sequence with a wait of three days, and starts it.
2. Step one sends; a contact replies; the owner marks the reply and step two is skipped for that contact.
3. The owner pauses the sequence, and contacts still waiting do not receive the next email.

SCREENS AND INFORMATION ARCHITECTURE
Build these as coherent responsive views. Each screen must specify its primary action, secondary actions, visible status, validation feedback, empty state, loading or pending state, success confirmation, and recoverable failure state.
1. Sequence editor: ordered steps, wait days, subject, body with first-name token, and start or pause.
2. Contacts: CSV import preview, status (queued, sent, replied, bounced), and search.
3. Outbox: each send, accepted or failed, time, and a retry that skips replied rows.
4. Reply inbox: the incoming message, mark-replied action, and the contact status after save.

CORE CAPABILITIES
1. a sequence with ordered steps, wait days, subject, and body tokens
2. CSV contact import with a preview and row errors
3. queued, sent, replied, and bounced states per contact
4. a send log with retry that skips replied and bounced rows
5. a reply inbox that marks the contact and cancels later steps

DETAILED BEHAVIOR AND BUSINESS RULES
Treat these as server-enforced product requirements, not interface suggestions:
1. Send only to contacts still queued for that step, and skip any contact marked replied, paused, or bounced.
2. Create one send log row per contact and step; a retry of an already-sent step does not email again.
3. Honor pause immediately so a worker that wakes after pause does not send.
4. Rate-limit sends, keep provider credentials off the client, and store unsubscribe or bounce as a terminal state.

DATA MODEL AND LIFECYCLE
Design a small relational schema centered on Sequence, Step, Contact, SendAttempt, Reply. Before implementing it, document:
1. Each table’s purpose, primary key, ownership or tenant boundary, timestamps, status fields, and important attributes.
2. Foreign keys, uniqueness constraints, check constraints, indexes needed by the named screens, and transaction boundaries for multi-record changes.
3. The allowed lifecycle or state transitions, who may trigger each transition, which transitions are terminal or reversible, and what audit history must remain immutable.
4. Archive, retention, and deletion behavior, including what happens to dependent records and external files.
5. Idempotency strategy for submissions, jobs, imports, notifications, webhooks, or retries where applicable.
Use migrations rather than ad-hoc schema creation. Store time instants consistently and retain named timezone context whenever local schedules or dates matter. Never rely on a counter, disabled button, or client-side check to preserve a business invariant.

USERS, AUTHENTICATION, AND PERMISSIONS
Implement only the roles required by the stated audience. Make the ownership and visibility model explicit before coding. Enforce authorization in every server-side query and mutation, including search, exports, attachments, live updates, and guessed URLs—not merely by hiding controls. Use secure session defaults, protect state-changing requests, and provide an understandable signed-out, expired-session, and forbidden state. Seed distinct users when multiple roles are required so permissions can be demonstrated and tested.

INTERACTION AND VISUAL DIRECTION
The product should feel fast, calm, focused, and credible rather than like a generic admin template. Use a clear visual hierarchy, restrained color, readable typography, generous hit targets, and consistent placement for primary actions. Start with server-rendered HTML and progressively enhance only the interactions that benefit from it. The core workflow must remain understandable if enhancement fails.

Render with TanStack Start and server-side React by default. Use server functions for authenticated form mutations and add client components only for interactions that genuinely require browser state, browser APIs, drag-and-drop, or live updates. The core workflow must remain understandable before client-side JavaScript finishes loading.

Design mobile layouts intentionally instead of simply stacking desktop panels. Support keyboard navigation, visible focus, semantic landmarks, explicit labels, useful page titles, reduced-motion preferences, and screen-reader announcements for asynchronous results. Never use color alone to communicate state. Destructive actions require clear scope and confirmation; safe repeated actions should be idempotent.

TECHNICAL DIRECTION
Build this version with Node.js and TanStack Start. Use TanStack Router for file-based routes, server functions for authenticated mutations, and server rendering for the first paint. Use a real SQL database with versioned migrations and an isolated test database. Access object storage through a server-only adapter, and run slow or retryable work in a real job or workflow system instead of the request lifecycle.

Keep domain rules in testable server-side modules instead of route handlers or UI components. Separate persistence, external providers, and background work behind small interfaces without building a framework. Prefer ordinary HTML forms and URLs for durable navigation; use optimistic interaction only when failure can be reconciled clearly.

The product brief currently identifies Astro, Workers, D1 as capability context. Preserve any required native, browser-only, edge, storage, real-time, or background-processing capability through a narrow adapter appropriate to the selected framework. If the core workflow genuinely requires native or browser APIs, keep that runtime as the primary execution surface rather than simulating inaccessible capabilities or inventing an unnecessary web surface.

Integrate with transactional email and Cloudflare Cron Triggers. For every integration:
- List required environment variables in an .env.example without real secrets.
- Add a small adapter with timeouts, normalized errors, and a deterministic local fake or development path.
- Verify inbound signatures and deduplicate provider events where supported.
- Keep credentials server-side, encrypt long-lived provider tokens at rest, and redact secrets and sensitive payloads from logs.
- Define retry, backoff, and idempotency behavior for any side effect that can be repeated.

SECURITY AND PRIVACY
Send only to contacts still queued for that step, honor pause and replied states in the worker, and keep provider credentials off the client.
Validate, normalize, and length-limit all untrusted input on the server. Escape rendered content by default, sanitize any intentionally accepted markup, rate-limit public or abuse-prone actions, and use private object storage plus short-lived authorized URLs for sensitive files. Collect the minimum personal data necessary for the named workflow. Document retention and deletion behavior. Add specific protections for the riskier surfaces in this app, such as uploads, redirects, outbound requests, email delivery, OAuth, webhooks, CSV import or export, and real-time connections.

ACCEPTANCE SCENARIOS
Automate these app-specific scenarios at the most appropriate level:
1. A contact marked replied after step one never receives step two.
2. Starting an already-running sequence does not duplicate queued sends.
3. An invalid CSV row is reported and no contacts from that file are saved.

TESTING
Add focused unit tests for state transitions, authorization predicates, normalization, date or money calculations, and other risky domain rules. Add integration tests for persistence constraints and each external adapter’s success, timeout, retry, and rejection paths. Add at least one browser-level test for every end-to-end journey above, including one small-screen viewport. Tests must use isolated data and run through a documented single command.

OPERATIONS AND FAILURE RECOVERY
Add structured server logs with request, job, or event correlation IDs but no secrets or unnecessarily sensitive data. Make failures actionable in both the interface and logs. Background work must expose pending, succeeded, failed, and retrying states where relevant; do not silently swallow errors. Include safe database migration and rollback guidance, seed data, backup and restore notes, external-data cleanup behavior, and a basic health or diagnostic path appropriate to the stack.

DELIVERABLES
Ship the working application, migrations, representative seed data, tests, .env.example, and a concise README. The README must cover prerequisites, local setup, environment variables, migrations, seed and test commands, deployment, integration setup, backup and restore, security decisions, and known limitations. Seed data should exercise the happy path plus at least one empty, failed, overdue, expired, archived, or permission-restricted state relevant to the product.

DEFINITION OF DONE
The app is complete when a fresh developer can follow the README, create and migrate the database, run the app, sign in as each relevant role, complete every named journey using real persisted data, refresh without losing state, recover from common failures, and use the core interface on phone and desktop. All acceptance scenarios pass, permission boundaries are covered by tests, and no core screen is left as a placeholder.

NON-GOALS
Do not build a lead database, LinkedIn automation, or a dialer. Hunter already covers saved email patterns. Mailchimp already covers a broadcast to a list.