In this post I'll give updates about open source I worked on during July and August 2026.
To see previous OSS updates, go here.
I'd like to thank all the sponsors and contributors who make this work possible. Without you, the projects below would not be as mature or would not exist or be maintained at all! So a sincere thank you to everyone who contributes to the sustainability of these projects.

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In the past two months it was summertime in Europe. Due to a couple of heatwaves, it was the perfect time to spend inside and enjoy my new air conditioning, while coding ;-).
The first half of July was mostly spent on improving performance and compatibility of SCI on CLJS. SCI now JIT-compiles interpreted function bodies to JavaScript at runtime, which closes a lot of the gap with compiled ClojureScript: a tight numeric loop went from ~175ms to ~7ms, over 20 times faster than the interpreter. Implementing core protocols on custom types now also works. There's hardly anything you can't do in SCI that you can do in compiled CLJS. I released new versions of scittle and nbb that take full advantage of this.
Also in the middle of July, clj-kondo got a pretty cool enhancement. It infers types of function arguments from how they are used. E.g. when you write (defn foo [x] (inc x)) we can infer that foo is a function that takes a number. I took this principle as far as I could while preventing false positives. Of course, clj-kondo supports the latest Clojure 1.13 destructuring changes too.
In the second half of July I spent significant time on improving babashka tasks with automatic help and completions, backed by babashka.cli. You can read all about that in this blog post: Babashka tasks with automatic help and completions
In August I had the pleasure of giving a talk about Reagami at Func Prog Sweden. In the talk I gave an interactive demo of how to use Reagami in a Squint project through a REPL. I also went into detail on the algorithm that powers the fast DOM diffing. While preparing for the talk, I added SSR to Reagami too. You can view the talk on YouTube:
The last few weeks of August I created babashka.ffi, a new namespace in babashka to call C libraries. See my previous blog post: Babashka 1.13.220 gets FFI. To validate the design I wrote four libraries with it: babashka.sqlite, babashka.duckdb, babashka.postgres and filewatcher. Each one exercised a different corner of the API, along with some examples based on raylib. PacMan is particularly cool:

Right now I'm looking forward to giving a babashka workshop at the Clojure/conj together with Rahul Dé. We're still polishing the workshop material behind the scenes and I'm excited to see how it's turning out. I'm sure it'll be a lot of fun and hope to catch many of you there.
In between all of this, I also worked on squint. It now supports the core protocols, so you can plug in your own collections and use them with core functions. E.g. you can use Immutable.js with Squint. I'm thinking about lightweight immutable persistent data structures for squint, but so far I haven't had much need for them, outside of Advent of Code puzzles.
The above was all about making existing projects better. But I also had a few new creative ideas:
Here are some highlights per project. See each project's CHANGELOG.md for the full list.
Babashka: native, fast-starting Clojure interpreter for scripting.
babashka.ffi: call C functions in shared libraries straight from babashka and JVM Clojure! See the guide--static and --dynamic options override the automatic selection:exec-args can sit directly on a task, not only under :cli, the way (exec ...) already reads it. Before, it was ignored on an :exec-fn or :cmd task:cli spec adds to the runner-level :tasks {:cli {:spec ...}} instead of replacing it. An option from the runner level keeps its coercion and default, and --help lists it under Inherited options:exec-fn runs when another task :depends on it. Before, it did nothing:exec-fn task named in :depends also parse for the CLI task that runs, with their coercion and default. --help lists them under Inherited options:cmd can be a symbol naming a var that holds the command tree, like :cli. Its namespace loads on demand:depends) too--help and shell completions, through the new :exec-fn and :cmd keys. See the blog post! These task keys should be considered experimental and may change in a future version of babashka, depending on feedback from the community:keys!, :syms!, :strs!, & inside a directive, :select, :all and :defaults. Adds req! and some-vals to clojure.coreclojure.core/Inst protocol on records, types and reify, and with extend-protocol and extend-typeproxy of java.io.Writer supports the one-argument write and append, so binding *out* to it works$HOME when the OS does not supply a home directory, e.g. for LDAP users in the static binary:eval and :print options of clojure.main/repl being ignored in the interactive REPL (@jeroenvandijk)babashka.ffi: call C functions in shared libraries from Clojure. New library, also usable from JVM Clojure. See the guide and the examples. The API is experimental
babashka.sqlite: SQLite for babashka through babashka.ffi
with-conn, queries, aggregates, transactions, last-insert-rowid, interrupt, and create-function! for defining a Clojure function callable from SQLbabashka.duckdb: DuckDB for babashka through babashka.ffi
babashka.postgres: PostgreSQL for babashka through babashka.ffi and libpq
connect, close!, with-conn, query, execute!, with-transaction, in-transaction?, cancel!, json, jsonb, version, server-version:read-json and :write-jsonwith-conn hook, CI on three operating systemsfilewatcher: watch files and directories from babashka
babashka.ffi: FSEvents on macOS, inotify on Linux, ReadDirectoryChangesW on Windows, and polling everywherecloseSCI: Configurable Clojure/Script interpreter suitable for scripting
js/Function. This is enabled by default and needs no configuration. When JIT is enabled, loops and numerical computations become much faster (and, in unrestricted contexts, JS interop too)eval is unavailable (e.g. under a Content Security Policy) SCI falls back to the interpreter. Results, error messages and error locations should be identical. And of course, it works under :advanced compilationjs/globalThis.SCI_DISABLE_JIT = true before loading SCI, or in your Google Closure compile settings with :closure-defines {sci.core/disable-jit true}instance? and js globals no longer fall back to the interpreterdeftype, defrecord and reify, and host code calling protocol methods on such instances dispatches into the sci implementations. Works under :advanced compilationdeftype and defrecord fields are JS accessors on the type's prototype: (.-field x) works on instances, (set! (.-field x) v) mutates deftype fields:unrestricted option on init and eval-string: when true, evaluated code may mutate built-in vars and CLJS instance interop skips :classes checks. The option applies only to the context it was passed toenable-unrestricted-access! now throws. Use the :unrestricted option instead. The old function set a process-global flag that leaked into nested contexts:async true in the attr map of defnaset on a primitive array was reflective and 170x slower than aset-doubleloop now report a located stack frame for the loop form instead of a frame without location (all platforms, including babashka)clj-kondo: static analyzer and linter for Clojure code that sparks joy.
(defn f [s] (subs s 1)) (f 42) will warn, since the evidence (subs s 1) tells us that s should be a string.(defn f [{:keys [x]}] (inc x)) (f {:x "foo"}) will warn. A key whose use rejects nil and that has no :or default is required.(defn cfg [] {:port "8080"}) (let [{:keys [port]} (cfg)] (inc port)) will warn.(inc (:y {})) will warn.if or the body of when when it is guarded by a known predicate. E.g. (if (string? x) (inc x) ...) will warn.clojure.core from 23 to 150 vars. E.g. (interleave 1 [2]) and (mod "a" 2) will warn.:constant-condition: warn on a condition whose truthiness is the same on every run. On by default. Replaces :condition-always-true, whose config and ignores still apply to always-true conditions, and takes over the cond catch-all warning from :unreachable-code:keys!, :syms! and :strs! and report them at call sites:select in map destructuring. The bound map's keys are known to the type checker:defaults in map destructuring, error when used without :or:analyze-call hook rewrites a call, clj-kondo checks the arity of the original function but not its parameter types.:discouraged-var: new per-var :positions option (a set or vector of :call and/or :value) to limit the warning to call position or value position. A var passed to a higher-order function such as map counts as :value.:seq-rest: suggest using (next x) over (seq (rest x)). Defaults to :off (@tomdl89)clojure.test.check.clojure-test/defspec#_ before an unmatched reader conditional discards the next form. E.g. [#_#?(:cljs 1) 2] reads as [] in :clj and will warn.comment forms no longer count for :shadowed-var, :unused-private-var and :inline-def.1.11.babashka CLI: Turn Clojure functions into CLIs!
:positional spec marker: positional args get their own Arguments: help section and may not be passed as options:restrict-args: error on positional args not consumed by :args->opts:cmd-aliases on a table entry or tree node gives a command one or more alternative names.:coerce takes the rest of its token as its value, like getopt: -J-Dfoo=bar binds "-Dfoo=bar", -p80 binds 80. Flag letters may precede the valued option in a cluster: with :b a flag and :a valued, -ba x parses as -b -a x:spec options under Inherited options:. The parser always accepted these options, but help did not show themformat-command-help accepts :spec, the dispatch-level spec, so a standalone call shows the same options as dispatchdispatch: the command named on the command line wins over the :exec-args of its ancestors. A value the user typed at an ancestor level still wins over both:enum values for validation, help and completion:doc and :epilog as a vector of lines, joined with newlines:cmd may be a vector of [name command] pairs, preserving command order without :cmd-order(repeat :k))parse-opts* resolves :spec so its :coerce/:collect entries steer parsing like in parse-opts--keep-order, so fish offers options in the order they are emitted, long option before its short alias, rather than sorting short options firstprefix-needed styleSquint: CLJS syntax to JS compiler
squint.immutable. Added a lot of protocols and made sure core functions work properly with themILookup, IAssociative, IMap, ICounted, IKVReduce, ICollection, IEmptyableCollection and IEquiv protocols. get, assoc, contains?, find, dissoc, count, reduce-kv, conj, empty and = dispatch to them on custom types. Plain objects and arrays keep their fast pathsIStack, IIndexed, IVector, IWriter and IPrintWithWriter protocols, write-all, and an ITransientVector -pop! slot; nth, peek, pop, pop!, subvec, vec, vector?, sequential?, set?, map?, seq, = and printing dispatch to custom collection typesequiv, hash, hash-ordered-coll, hash-unordered-coll and the IHash protocol. hash follows equiv: plain mutable objects and arrays hash by referenceIMeta and IWithMeta protocols; meta and with-meta dispatch through them and the internal meta symbol property is goneclojure.set dispatches through the collection protocols: results keep the input's type, membership tests against a protocol set are value-based, and rename-keys/map-invert no longer mutate a recorddefrecord, record? and the IRecord marker protocol. Records store their fields as own string-keyed properties and implement the map-facing protocols, so keyword lookup, keys, seq, assoc, conj and = work through the regular core functions. assoc keeps the record type, dissoc of a basis field gives a plain map, printing gives #TypeName{:a 1}:keys!/:syms!/:strs! for required keys, & inside them for keys required but not bound, :select, :all, :defaults, and :or by key& {:keys [...]} now destructures a map instead of the raw rest args, and a seq destructured as a map is read as kwargsrecur inside try no longer emits an illegal continue:as-alias in ns :require like CLJS: no runtime import, only a compile-time alias so a namespaced keyword such as ::alias/x resolves:require-global and :refer-global to ns, binding globals loaded via a script tag to consts without emitting an import:squint/compile-time opt-in mechanism for macro/compile-time namespaces. See doc/compile-time.mddefmacro is compile-time only: no longer emitted to the runtime module, and :refering a macro no longer emits a runtime import for it, matching CLJS^:dev/after-load + ^:dev/before-load hooks similar to shadow-cljs.indexOf on a lazy seq now uses reference equality like a JS array, not value equality. This diverges from CLJS but keeps = out of any bundle that only builds lazy seqs, shrinking a conj bundle from 3801 to 2215 bytesSymbol.for for protocol method dispatch, so pulling in multiple copies of squint.core (e.g. via http://esm.sh/) does not break protocol dispatchCherry: Experimental ClojureScript to ES6 module compiler
cherry.test with clojure.test-compatible testing API, requirable as cljs.test or clojure.testcherry.test/report is a multimethod dispatching on [*current-reporter* type] like cljs.test, so reporting can be extended with defmethod^:dev/after-load / ^:dev/before-load hot-reload hooks, sharing squint's implementation: import cherry from 'cherry-cljs/vite.js'reify, defmulti/defmethod and the vswap! macro. #'foo emits foo's value, like squintset! and binding work across ESM modules. cljs.core dynamic vars are exported as accessor boxes proxying the real vardefprotocol :extend-via-metadata impls resolve under the fully qualified method symbol, so replicant's mutation-log renderer works: replicant's own test suite passes under cherrydeftype implementing cljs.core protocols such as Inst, IIterable and IAtom: their marker properties were Closure-renamed in the precompiled core and missing from the emitter's core protocol set. The externs list and the set are now generated from cljs.core's protocols (bb gen-externs) and the build fails on driftPROTOCOL_SENTINEL with coexisting CLJS runtimes in the same JS realm{:squint/compile-time true} load only their compile-time part into the macro environment, like squint--help/-h, argument validation and error messages via babashka.cli's dispatch, like squint. Adds watch and nrepl-server commands, shell tab completion, and reads options from cherry.edn instead of squint.ednChoq: a ~5 MB binary running the cherry compiler on embedded QuickJS
url and util, @babashka/fs, and a test runnerBuzz: write a web application with the JVM or babashka only
tube-pod: turn YouTube videos into a private podcast
yt-dlp, writes an RSS feed and serves bothmulti-snake: snake for as many players as show up
Reagami: A minimal zero-deps Reagent-like for Squint and CLJS
reagami.ssr to render hiccup to an HTML string on the JVM, Babashka, Squint and CLJS. See Server-side renderingreagami.core/render (the regular render function) now hydrates a server-rendered page. It adopts the existing DOM instead of clearing the rootnpm create reagami-app my-app to create a Vite project with hot reload and a browser nREPL:on-render now takes a map: (fn [{:keys [node lifecycle state save]}]). Call save with a value to keep it for the next call, and read it back as state. In previous versions, the hook took three arguments and its return value became the statemoveBefore where the browser has it, so a moved subtree keeps its iframe state, animations, focus and selection (#54)value, checked, selected and disabled on a tag with a hyphen as attributes, not as JS properties. A custom element observes attributes, so a property never had any effect. Native elements still handle them as properties:on-rated, now reach the element through addEventListener, because a browser only wires an on* property for standard events<todo-list> custom element, used from Squint, from JavaScript with and without Reagami:on-render nodes and other :on-render improvementscljbang: a Clojure-like language that runs as Emacs Lisp
fn and defn, loop/recur with a tail position check, try/throw/ex-info, case, atoms, syntax quote including nesting, &form and &env in macros, regex and set literals, #_, edn/read-string, slurp and spitel! for calling Emacs Lisp names that are not valid Clojure symbolsnbb: Scripting in Clojure on Node.js using SCI
js/Function. This is enabled by default. This makes loops, numerical computations and JS interop much fasterglob, copy, move, create-dirs, delete-tree, with-temp-dir, path helpers and more) is available via (require '[babashka.fs :as fs]), matching BabashkaILookup, etc) on deftype and defrecorddeftype/defrecord field interop, set! on ^:unsynchronized-mutable fields, add cljs.core type classes like PersistentHashMap, write-all and goog.math.Longprn in nREPLScittle: Execute Clojure(Script) directly from browser script tags via SCI
js/Function. This is enabled by defaultreagent to 1.2.0, re-frame to 1.4.7, replicant to 2026.06.2 and shadow-cljs to 3.4.11squint-inline: write squint functions and inline expressions in a ClojureScript project
assoc, update-in and select-keys work on those without js->clj and clj->js:js-provider :import, and each function's tree-shaken size is recordedEdamame: configurable EDN and Clojure parser with location metadata and more
:refer + rename in :auto-resolve-ns:auto-resolve-ns, qualify syntax-quoted imported classes (e.g. `Date with (:import [java.util Date])) with the full classname:auto-resolve-ns, leave method, constructor and dotted syntax-quoted symbols (`.toString, `Bar., `foo.bar) as-is, matching Clojurefs: file system utility library for Clojure
@babashka/fs npm packagehttp-client: HTTP client for Clojure and babashka
http-server: serve static assets
Content-Range last-pos per RFC 9110, suffix ranges (bytes=-N, previously a 500), clamping last-pos beyond EOF, reading the full range, and a test suite (@slagyr)Cream: Clojure + GraalVM Crema native binary
pom.xml when there is no deps.edn, and recompile Java sources when a dependency changedgraaljs-cherry: a native-image cherry REPL on GraalJS
--small build without itclj-kondo-browser: a static Clojure source browser built from clj-kondo analysis
grasp: Grep Clojure code using clojure.spec regexes
deps.clj: a faithful port of the Clojure CLI Bash script to Clojure
lein-clj-kondo and clj-kondo-bb: released alongside each clj-kondo release
These are some other projects I'm involved with, but little to no activity happened in the past two months.
Published: 2026-09-02
Tagged: clojure oss updates