diff --git a/plans/agent-briefings/primitives-loop.md b/plans/agent-briefings/primitives-loop.md
index 84cbb654..36893ecf 100644
--- a/plans/agent-briefings/primitives-loop.md
+++ b/plans/agent-briefings/primitives-loop.md
@@ -54,7 +54,9 @@ Steps:
       primitives in `hosts/ocaml/sx_primitives.ml` (or equivalent); wire into evaluator.
       Note: Vector type + most prims were already present; added bounds-checked vector-ref/set!
       and optional start/end to vector-copy. 10/10 vector tests pass (r7rs suite).
-- [ ] Spec: add vector entries to `spec/primitives.sx` with type signatures and descriptions.
+- [x] Spec: add vector entries to `spec/primitives.sx` with type signatures and descriptions.
+      All 10 vector primitives now have :as type annotations, :returns, and :doc strings.
+      make-vector: optional fill param; vector-copy: optional start/end (done prev step).
 - [ ] JS bootstrapper: implement vectors in `hosts/javascript/platform.js` (or equivalent);
       ensure `sx-browser.js` rebuild picks them up.
 - [ ] Tests: 40+ tests in `spec/tests/test-vectors.sx` covering construction, ref, set!,
@@ -196,5 +198,6 @@ Brief each language's loop agent (or do inline) after rebasing their branch onto
 
 _Newest first._
 
+- 2026-04-25: Phase 1 spec step done — all 10 vector primitives in spec/primitives.sx have full :as type annotations, :returns, :doc; make-vector optional fill param added.
 - 2026-04-25: Phase 1 OCaml step done — bounds-checked vector-ref/set!, vector-copy now accepts optional start/end, spec/primitives.sx doc updated. 10/10 r7rs vector tests pass, 4747 total (394 pre-existing hs-upstream fails unchanged).
 - 2026-04-25: Phase 0 complete — stopped CL/APL/Ruby/Tcl loops (all 4 idle at shell); confirmed E38 (tokenizer :end/:line) and E39 (WebWorker stub) both have implementation commits.
diff --git a/spec/primitives.sx b/spec/primitives.sx
index ddbbaf60..70cf5177 100644
--- a/spec/primitives.sx
+++ b/spec/primitives.sx
@@ -170,15 +170,15 @@
 
 (define-primitive
   "make-vector"
-  :params ((n :as number))
+  :params ((n :as number) (fill :as any :optional true))
   :returns "vector"
-  :doc "Create vector of size n, optionally filled.")
+  :doc "Create vector of length n, each element initialised to fill (default nil).")
 
 (define-primitive
   "vector"
-  :params ()
+  :params (:rest (elts :as any))
   :returns "vector"
-  :doc "Create vector from arguments.")
+  :doc "Construct a vector from its arguments.")
 
 (define-primitive
   "vector?"
@@ -190,31 +190,31 @@
   "vector-length"
   :params ((v :as vector))
   :returns "number"
-  :doc "Number of elements.")
+  :doc "Number of elements in vector v.")
 
 (define-primitive
   "vector-ref"
   :params ((v :as vector) (i :as number))
   :returns "any"
-  :doc "Element at index.")
+  :doc "Element at 0-based index i. Error if out of bounds.")
 
 (define-primitive
   "vector-set!"
   :params ((v :as vector) (i :as number) (val :as any))
   :returns "nil"
-  :doc "Set element at index.")
+  :doc "Mutate element at index i to val. Error if out of bounds.")
 
 (define-primitive
   "vector->list"
   :params ((v :as vector))
   :returns "list"
-  :doc "Convert vector to list.")
+  :doc "Convert vector to a fresh list.")
 
 (define-primitive
   "list->vector"
   :params ((l :as list))
   :returns "vector"
-  :doc "Convert list to vector.")
+  :doc "Convert list to a fresh vector.")
 
 ;; --------------------------------------------------------------------------
 ;; Core — Predicates
@@ -223,7 +223,7 @@
   "vector-fill!"
   :params ((v :as vector) (val :as any))
   :returns "nil"
-  :doc "Fill all elements.")
+  :doc "Set every element of v to val in place.")
 
 (define-primitive
   "vector-copy"