Productivity · Side quest build

Build your own Slack

Your team may need three channels, not 3,000 integrations. Slack charges $15–$18 per person per month — that’s $180–$216 a year per person — for something you can replace with focused software of your own. Here is the honest scope, the honest timeline, and the exact prompt to hand your coding agent.

from 4 daysOnly for a focused team

Who this replacement is for

This build targets a small internal team that wants searchable asynchronous conversation. The goal: support a handful of durable topic channels without recreating an entire chat ecosystem. If you need more than that, keep paying — the point of building it yourself is owning a tool shaped exactly like your workflow, not re-implementing a venture-funded roadmap.

How long it actually takes

One number would be a lie, so here are three. Each tier is a real, usable product — pick the one that matches how much of Slack you actually use.

EstimateWhat you get
4 dayschannels, messages, threads
2 weeks+reactions, file uploads, search, unread markers
3 months+voice calls, app platform, mobile apps — the part you should probably skip

What a minimal Slack alternative needs

Data model

Workspace, Channel, Membership, Message, Reaction

Integrations

company OAuth, object storage, email

Capability context

Astro, Durable Objects, D1

The guardrail

Treat private-channel authorization as a server-side invariant and rate-limit posting.

Deliberate non-goals

Do not build voice calls, app bots, external guests, enterprise retention controls, or mobile apps.

The complete build prompt

Copy this into your coding agent of choice. It is scoped for a useful v1 — journeys, screens, business rules, data model, security, tests, and acceptance scenarios included. Pick your stack:

You are building a production-ready software product named “Campfire”, a deliberately focused alternative to Slack. 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: a small internal team that wants searchable asynchronous conversation.
Primary outcome: support a handful of durable topic channels without recreating an entire chat ecosystem.
Product principle: optimize the exact workflow below instead of copying the full breadth of Slack. 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. A workspace admin signs in through company OAuth, creates public project channels and a private leadership channel, then manages membership for the private channel.
2. A teammate posts a message with an attachment, edits a typo, receives emoji reactions, and continues a focused discussion in a thread.
3. A returning teammate opens their unread channel markers, searches by phrase and author, jumps to the matching message in context, and configures an email digest.

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. Conversation shell: channel sidebar with public, joined private, and unread states; active message stream; composer; member presence hints; and jump-to-latest control.
2. Channel detail: chronological messages, date separators, attachment cards, reaction summaries, edit and delete menus, thread counts, and unread boundary.
3. Thread panel: parent message, ordered replies, participant list, reply composer, reactions, attachment support, and return-to-channel context.
4. Search and workspace settings: phrase, channel, person, and date filters; highlighted results; channel membership controls; digest schedule; and attachment limits.

CORE CAPABILITIES
1. public and private channels with membership controls
2. messages, threads, emoji reactions, edits, and deletes
3. file attachments and unfurled internal links
4. full-text search by channel, person, and date
5. unread markers and an email digest instead of push notifications

DETAILED BEHAVIOR AND BUSINESS RULES
Treat these as server-enforced product requirements, not interface suggestions:
1. Check workspace and private-channel membership server-side for every read, search, post, reaction, attachment, and live-update subscription.
2. Give messages and replies stable sequence positions; persist them before broadcast so reconnecting clients can request all events after their last cursor.
3. Edits retain original author and edited time, while deletes become permission-safe tombstones so thread order and audit history remain coherent.
4. Store attachments privately, validate type and size before completion, serve them through short-lived signed URLs, and rate-limit posting by member and workspace.

DATA MODEL AND LIFECYCLE
Design a small relational schema centered on Workspace, Channel, Membership, Message, Reaction. 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. Use HTMX for form submissions, partial navigation, and server-driven updates, then Alpine.js only for small local browser state. The core workflow must remain understandable if either enhancement layer 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 the AHA stack: Astro for routing, layouts, and server-rendered pages; HTMX for interactions that benefit from HTML fragment responses; and Alpine.js for small, local interface state. 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, Durable Objects, 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 company OAuth and object storage and email. 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
Treat private-channel authorization as a server-side invariant and rate-limit posting.
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. Given a member outside a private channel, when they guess its URL or search for its contents, no channel metadata, message, or attachment is disclosed.
2. Given a client disconnects after posting but before receiving confirmation, when it retries with the same idempotency key, exactly one message appears.
3. Given unread messages and thread replies since a member’s last visit, when they open the channel, the boundary is correct and marking read advances monotonically.

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 voice calls, app bots, external guests, enterprise retention controls, or mobile apps.

Frequently asked questions

How long does it take to build your own Slack?

A basic version — channels, messages, threads — takes about 4 days. Roughly 2 weeks+ gets you a solid v1 with reactions, file uploads, search, unread markers. Matching everything Slack really does (voice calls, app platform, mobile apps) is closer to 3 months+, which is exactly why you should scope down instead.

How much does Slack cost if I keep subscribing?

Slack runs $15–$18 per person per month on public paid plans, which is $180–$216 per year for every person on your team. A focused self-built replacement costs your build time plus close-to-zero hosting.

What stack should I use to build a Slack alternative?

The build prompt on this page ships in four flavors: the AHA stack (Astro, HTMX, Alpine.js), Next.js, Laravel, and Ruby on Rails. The capability context for this product is Astro, Durable Objects, D1. Pick the stack you already know — the scope matters more than the framework.

What features does a minimal Slack replacement need?

A useful v1 needs: public and private channels with membership controls; messages, threads, emoji reactions, edits, and deletes; file attachments and unfurled internal links; full-text search by channel, person, and date; unread markers and an email digest instead of push notifications. Everything else is scope creep until you personally miss it.

What should I deliberately not build?

Do not build voice calls, app bots, external guests, enterprise retention controls, or mobile apps.

Prompt copied. Go ship it.