Convex + Next.js

Use this skill to

• Bootstrap Convex in a new or existing Next.js app.
• Add a feature end to end: schema, indexes, functions, UI hooks, auth, and deployment.
• Debug typical integration failures: missing provider, missing generated code, bad client/server boundaries, missing env vars.
• Review whether Convex is a good fit for a realtime or collaborative Next.js feature.

Do not use this skill when

• The task is plain Next.js UI work with no Convex dependency.
• The backend is definitely not Convex and the user is not considering migration.
• The problem is generic database theory with no Next.js/Convex implementation work.

Default posture

• Use npx convex dev for development.
• Keep reactive hooks in Client Components.
• Prefer indexed queries over .filter(...).
• Treat unbounded lists as paginated by default.
• Put external I/O in actions; add "use node" only if Node APIs or unsupported packages are required.
• Require input validation on public functions; add return validation unless there is a good reason not to.
• Add explicit auth and ownership checks for user data.
• Prefer helper functions or custom wrappers when the same auth/tenant checks repeat.

Starting questions to answer from the repo

1. Is this a new app, an existing Next.js app, or a migration?
2. App Router, Pages Router, or both?
3. Does the feature need reactivity, SSR, server actions, or all three?
4. Is the dataset bounded or should it paginate?
5. Is auth already present? If yes, is it client-only or needed on the server too?
6. Would a Convex component make this feature more reusable or isolated?

Workflow 1 — Choose the right starting path

A. Brand new project

Prefer:

npm create convex@latest

If the user already has a Next.js app structure they want to keep, use path B instead.

B. Existing Next.js app

Install Convex and start dev sync:

npm install convex
npx convex dev

Expected outcomes:

• convex/ exists, or the custom functions directory from convex.json
• generated files appear under _generated/
• a dev deployment or local deployment is connected
• NEXT_PUBLIC_CONVEX_URL is available for the frontend

See references/01-setup-and-decision-tree.md.

Workflow 2 — Model data for query patterns, not screen shapes

Before writing UI, define:

• the tables
• the ownership fields
• the indexes needed for the main reads
• whether lists are bounded or paginated
• whether files should live in Convex File Storage instead of large documents

Rules:

• Prefer flat relational-style documents over deep nested blobs.
• Use v.id("table") for relationships.
• Add indexes for every repeated filter/sort path you know you need.
• If the query would scan an unbounded table, redesign the index or paginate it.

See references/02-schema-and-indexes.md.

Workflow 3 — Pick the correct Convex function shape

Query

Use for pure reads. Keep them small, indexed, and predictable.

Mutation

Use for writes and transactional read-write logic.

Action

Use for external APIs, long-running work, or non-transactional orchestration.

• Stay in the default Convex runtime if fetch is enough.
• Add "use node" only when you need Node-only APIs or unsupported packages.
• Files with "use node" should contain actions only.

Detailed patterns: references/03-functions-and-safety.md

Workflow 4 — Enforce validation, auth, and ownership early

For public functions:

• define args
• usually define returns
• call ctx.auth.getUserIdentity() when the function is protected
• check ownership or team membership, not just authentication
• move repeated checks into helpers or custom wrappers once duplication starts to spread

If auth or tenant checks repeat in many functions, consider:

• convex/lib/auth.ts helpers
• thin wrappers/custom functions for query, mutation, or action
• shared policy helpers for tenant/resource checks

See references/05-auth-and-access-control.md.

Workflow 5 — Respect Next.js boundaries

• useQuery, useMutation, useAction, usePaginatedQuery, and usePreloadedQuery belong in Client Components.
• For reactive-first pages with good first paint, use preloadQuery in a Server Component and usePreloadedQuery in a Client Component.
• For server-only reads, use fetchQuery.
• For Server Actions or Route Handlers, use fetchMutation or fetchAction.

Do not call React hooks from Server Components.

See references/04-nextjs-client-and-server-boundaries.md.

Workflow 6 — Treat large lists as a pagination problem

Use pagination by default when:

• the user says “all”, “feed”, “activity”, “history”, “messages”, “notifications”, “search results”, or “infinite scroll”
• the table can grow without a natural hard limit
• you would otherwise reach for .collect() on a user-facing list

Pattern:

• backend query uses .paginate(paginationOpts)
• React client uses usePaginatedQuery

See references/06-pagination-performance-and-realtime.md.

Workflow 7 — Consider components when the feature wants isolation

A Convex component is often worth it when the feature:

• has its own schema, functions, and internal jobs
• should be reusable across apps
• would otherwise pollute the root convex/ folder with tightly-coupled code

Use normal app code when the feature is small and specific to one app.

See references/07-components-migrations-and-reuse.md.

Workflow 8 — Choose the right development mode

• On your own machine or in a local coding agent, standard npx convex dev is usually right.
• In remote or background agents that cannot log in, use Agent Mode.
• For isolated local-only development, use local deployments.

See references/08-local-dev-agent-mode-and-cloud-agents.md.

Workflow 9 — Validate before you stop

Run:

python {baseDir}/scripts/validate_project.py --root .

Useful flags:

python {baseDir}/scripts/validate_project.py --root . --strict
python {baseDir}/scripts/validate_project.py --root . --json

The validator checks for the common failures this skill is designed to catch:

• missing Convex installation or generated code
• missing provider or env wiring
• hook usage in non-client components
• implicit table access
• .collect() or .filter() smells in queries
• missing validators on Convex functions
• risky "use node" file mixes
• scheduler calls aimed at public functions
• missing TypeScript strictness or missing Convex ESLint plugin

Workflow 10 — Deploy cleanly

During normal development, keep using:

npx convex dev

For production or CI:

npx convex deploy

For Vercel builds, the common pattern is:

npx convex deploy --cmd "npm run build"

See references/09-deploy-ci-and-vercel.md.

What a strong final implementation usually includes

• updated convex/schema.ts
• new or updated indexes
• public functions with args and usually returns
• auth or ownership checks where needed
• UI wired through the generated api
• "use client" only where it is actually needed
• paginated lists instead of unbounded collects
• a note about required env vars
• commands the user should run to verify the change

Response shape to prefer when making code changes

1. State the files to add or edit.
2. Explain the architectural choice in one sentence.
3. Apply the code changes.
4. Run the validator or describe the exact checks to run.
5. Call out any follow-up env vars, auth setup, deploy steps, or migration concerns.

Reference map

• Setup and choosing a path: references/01-setup-and-decision-tree.md
• Schema and index design: references/02-schema-and-indexes.md
• Functions, validation, Node actions, scheduler safety: references/03-functions-and-safety.md
• Next.js client/server boundaries and SSR: references/04-nextjs-client-and-server-boundaries.md
• Auth and access control: references/05-auth-and-access-control.md
• Pagination, performance, and realtime: references/06-pagination-performance-and-realtime.md
• Components, migrations, and reuse: references/07-components-migrations-and-reuse.md
• Local dev, Agent Mode, and local deployments: references/08-local-dev-agent-mode-and-cloud-agents.md
• Deploy and CI: references/09-deploy-ci-and-vercel.md
• Troubleshooting and smoke tests: references/10-troubleshooting-and-smoke-tests.md