ufWhy uf
uf and Next.js
Next.js is the framework uf has to be measured against, so this page is the audit: every App Router feature in one row, with uf's answer and one of four words beside it. The words are the point. A row marked Planned is a feature you cannot use today, whatever the rest of the table says.
What you will be able to do: check whether the Next.js feature your application depends on exists in uf, in what shape, and where it is tracked when it does not.
What you need first: nothing installed. uf compared is the shorter version, and says when to choose Next.js instead.
| Word | Means |
|---|---|
| Implemented | code and tests on main |
| Partial | implemented, with the hole named in the row |
| Planned | no code yet; the issue is linked |
| Refused | a decision not to, with the reason on the linked page |
#1357 is the issue this table is kept from. A pull request that changes a row changes both.
What kind of server this is
uf's server half is a backend for this frontend: route handlers, server actions and rendering, sized to what the interface needs. It is not where a team's domain lives. Your services, their database and their business rules stay where they are, and a uf application talks to them. That is why several Next.js rows below end in "use a route handler" or "Refused": a framework that grows a backend grows a second place for the domain to live.
It is also why no row depends on a hosting company. Server features run on
uf start and on the server adapters, each target says what it cannot do, and
what a static host cannot run is refused by name at build time rather than
dropped.
Routing
| Next.js | uf | Status |
|---|---|---|
page, layout, template, loading, error, not-found, default | $page.js, $layout.js, $template.js, $loading.js, $error.js, $not-found.js, $default.js (Routing) | Implemented |
unauthorized.js, forbidden.js | one $error.js; unauthorized() and forbidden() arrive as cases of RouteError and answer 401 and 403 | Implemented, one file on purpose |
global-error.js | a throw in the root layout, or in $error.js itself, reaches a framework boundary that renders uf's own page | Partial: a project cannot supply that page |
route.js | $route.js, which may also export QUERY | Implemented |
middleware.ts, one at the root | $middleware.js at any depth, chosen by the request path and never by a header (Answering requests) | Implemented |
(group) | (group) | Implemented |
[slug], [...slug] | the same | Implemented |
[[...slug]], the optional catch-all | nothing; write [...slug] and a page at the parent path | Planned, #1361 |
@slot parallel routes | the same (Parallel routes) | Implemented |
(.), (..), (...) intercepting routes | the same markers, only inside a slot, under Server Components and without them (Intercepting routes) | Implemented |
redirects, rewrites, headers in next.config | app.router in uf.config.js | Implemented |
basePath, trailingSlash | the same names | Implemented |
| i18n routing | @uniflowed/i18n/routing (i18n) | Implemented |
Rendering and data
| Next.js | uf | Status |
|---|---|---|
| React Server Components | React's own Flight payload, from react-server-dom-parcel (Server Components) | Implemented |
| Streaming and Suspense | HTML streaming on uf start and every server adapter but serverless, which buffers | Implemented; Partial on serverless |
| Partial prerendering | ppr: a static shell with holes streamed per request (Rendering) | Implemented |
Static generation, generateStaticParams | the same name | Implemented |
ISR and revalidate | isr, kept on disk, in Workers KV or in a store you name (Rendering) | Implemented |
revalidatePath, revalidateTag | the same names (Caching) | Implemented |
| The fetch cache | opt-in per request (Caching) | Implemented |
unstable_cache, "use cache" | cacheFunction, named explicitly; a blanket data cache is refused | Partial, a different shape |
after() | after() from @uniflowed/server | Implemented |
cookies(), headers(), draftMode() | the same names | Implemented |
connection() | nothing | Planned |
instrumentation.js, OpenTelemetry | instrumentation.js and request spans | Implemented |
Server actions
| Next.js | uf | Status |
|---|---|---|
Exported functions of a "use server" module, callable from the client | the same, with ids that are an HMAC of the build and a closed JSON grammar for arguments (Server actions) | Implemented |
useActionState, useFormStatus, useOptimistic | React's own | Implemented |
A <form action={serverFunction}> that submits before hydration | a urlencoded native post to the page, answered with the page rendered with useActionState's new state, behind Origin and Sec-Fetch-Site (Before the page hydrates) | Implemented; no multipart, so no file fields |
| A server function passed to a client component as a prop | the client component imports the "use server" module instead | Planned, #1359 |
Inline "use server" closures, with their captured variables encrypted | recognised and keyed, not callable | Planned, #1360 |
| A file upload through an action | refused at the call site; use a route handler | Refused |
| Caching an action's result | rendering.cache.actions is refused when the config loads | Refused |
Metadata and assets
| Next.js | uf | Status |
|---|---|---|
metadata, generateMetadata, JSON-LD | the same names (Metadata) | Implemented |
sitemap.js, robots.js | sitemap.xml and robots.txt, written by uf build from the route table and site.url | Implemented, generated rather than authored |
opengraph-image, rendered to a PNG | a card template; uf ships no rasteriser (An Open Graph card) | Partial |
next/image | build-time resizing with srcset and a blur placeholder, and /__uf/image behind remotePatterns for remote images (Images) | Implemented; no AVIF at build time, which is refused |
next/font | imported fonts self-hosted with a metric-matched fallback; nothing downloaded from a provider | Partial |
next/script loading strategies | nothing | Planned |
Types
The rows where Flow should put uf ahead rather than level.
| Next.js | uf | Status |
|---|---|---|
typedRoutes, which checks <Link href> | a generated route() builder whose paths and parameters uf check checks (Types for routes); <Link to> and router.push still take any string | Partial |
| Route parameters | typed per route in the generated router.js | Implemented |
searchParams | { [string]: string }, and a repeated key keeps one value | Planned: a page declares a Validator schema and receives its output type, #1362 |
| Whether an action's arguments can cross the network | uf prepare holds every action's arguments and result against the wire grammar in one uf check (The types the wire needs) | Implemented; Next.js has no equivalent |
Where it runs
| Target | Written by | Tested | Deployed to the real platform by uf's pipeline |
|---|---|---|---|
uf start, uf preview on Node.js, Bun or Deno | uf build | yes | not applicable |
| Node.js, container | --adapter node, --adapter container | yes, including a parity harness against a built artefact | no (#956) |
| Bun, Deno | --adapter bun, --adapter deno | yes, in process | no |
| Cloudflare Workers | --adapter edge | yes, under Wrangler's local runtime | no |
| AWS Lambda | --adapter serverless, bodies buffered | yes, in process | no |
| Any static host | --adapter static, which refuses server features by name | yes | not applicable |
| One executable | --compile, with no cache | yes | not applicable |
Deploy a web build has what each one needs and what it refuses.
Measured against Next.js
From tools/bench/toolchain/baseline.json: the Bench workflow on a 32-core AMD
EPYC runner, Next.js 16.3.6 against uf 0.0.0-alpha.46, each the median of
seven runs on the same generated application. Benchmarks
has every row and how it was taken.
| Stage | uf | Next.js |
|---|---|---|
| dev server, first document, cold | 1,099 ms | 1,014 ms |
| dev server, first document, warm | 875 ms | 1,020 ms |
| build, cold | 2,547 ms | 3,053 ms |
| build, warm | 2,419 ms | 1,399 ms |
| production server throughput | not measured | not measured |
uf loses the cold dev start by about 8% and the warm build by about 1.7 times.
There is no production-server comparison yet, so nothing on this site claims uf
renders faster than next start;
#1363 adds that row.
Where to go next
uf and Vite+ is next: the toolchain uf is most often compared to, and why the two answer different questions.
Edit this pagedocs/app/guide/nextjs/$page.mdx