diff --git a/src/package-catalog/api.rkt b/src/package-catalog/api.rkt
new file mode 100644
index 0000000..75fdd22
--- /dev/null
+++ b/src/package-catalog/api.rkt
@@ -0,0 +1,2 @@
+#lang racket/base
+
diff --git a/src/package-catalog/db.rkt b/src/package-catalog/db.rkt
new file mode 100644
index 0000000..e12847a
--- /dev/null
+++ b/src/package-catalog/db.rkt
@@ -0,0 +1,46 @@
+#lang racket/base
+
+(provide make-db
+         db?
+         db-has-key?
+         db-ref
+         db-set!
+         db-remove!
+         db-keys)
+
+(require racket/file)
+
+(struct db (name path serializer deserializer) #:transparent)
+
+(define (make-db name path serializer deserializer)
+  (make-directory* path)
+  (db name path serializer deserializer))
+
+(define (check-key what db key)
+  (unless (string? key)
+    (error what "Invalid key for db ~a: ~v" (db-name db) key)))
+
+(define (db-has-key? db key)
+  (check-key 'db-has-key? db key)
+  (file-exists? (build-path (db-path db) key)))
+
+(define (db-ref db key default-thunk)
+  (check-key 'db-ref db key)
+  (define p (build-path (db-path db) key))
+  (if (file-exists? p)
+      ((db-deserializer db) (file->value p))
+      (default-thunk)))
+
+(define (db-set! db key value)
+  (check-key 'db-set! db key)
+  (write-to-file value (build-path (db-path db) key)
+                 #:exists 'replace))
+
+(define (db-remove! db key)
+  (check-key 'db-remove! db key)
+  (define p (build-path (db-path db) key))
+  (when (file-exists? p)
+    (delete-file p)))
+
+(define (db-keys db)
+  (map path->string (directory-list (db-path db))))
diff --git a/src/package-catalog/main.rkt b/src/package-catalog/main.rkt
new file mode 100644
index 0000000..dfdb674
--- /dev/null
+++ b/src/package-catalog/main.rkt
@@ -0,0 +1,7 @@
+#lang racket/base
+
+(provide (all-from-out "structs.rkt")
+         (all-from-out "source.rkt"))
+
+(require "structs.rkt")
+(require "source.rkt")
diff --git a/src/package-catalog/source.rkt b/src/package-catalog/source.rkt
new file mode 100644
index 0000000..7e14a4a
--- /dev/null
+++ b/src/package-catalog/source.rkt
@@ -0,0 +1,182 @@
+#lang racket/base
+
+(provide (struct-out url-source)
+         (struct-out git-source)
+         package-source?
+         string->package-source
+         package-source->string
+         github-source?
+         github-user+repo)
+
+(require racket/match)
+(require net/url)
+(require pkg/name)
+(require pkg/private/repo-path)
+(require (only-in racket/string string-join))
+
+(struct url-source (url ;; String
+                    )
+        #:prefab)
+(struct git-source (host ;; String
+                    port ;; Nat or #f
+                    repo ;; String (e.g. for github.com, "/user/repo")
+                    branch ;; String
+                    path ;; Relative URL String
+                    )
+        #:prefab)
+
+(define (package-source? x)
+  (or (url-source? x)
+      (git-source? x)))
+
+(define (string->package-source str)
+  (define u (string->url str))
+  (define-values (_name type) (package-source->name+type str #f))
+  (cond
+   [(memq type '(git github))
+    (define-values (host port repo branch path)
+      (if (equal? "github" (url-scheme u))
+          (match (split-github-url u)
+            [(list* user repo branch path)
+             (values "github.com" #f (string-append user "/" repo) branch path)]
+            [(list user repo)
+             (values "github.com" #f (string-append user "/" repo) "master" '())]
+            [_ (error 'string->package-source "Invalid github url: ~v" str)])
+          (split-git-url u)))
+    ;; TODO: clean this up in repo-path.rkt
+    (git-source host
+                port
+                repo
+                branch
+                (string-join path "/"))]
+   ;; [(and (member (url-scheme u) '("http" "https"))
+   ;;       (equal? (url-host u) "github.com"))
+   ;;  ;; ... parse the path, etc., and turn it into a git-source ...
+   ;;  ]
+   [else
+    (url-source (url->string u))]))
+
+(define (package-source->string s)
+  (match s
+    [(url-source u) u]
+    [(git-source host port repo branch path)
+     (url->string (url "git"
+                       #f
+                       host
+                       port
+                       #t
+                       (url-path (path->url repo))
+                       (if (string=? path "")
+                           '()
+                           (list (cons 'path path)))
+                       branch))]))
+
+(define (github-source? s)
+  (unless (package-source? s) (error 'github-source? "Expected package-source: ~v" s))
+  (match s
+    [(git-source "github.com" #f (regexp "^([^/]+)/([^/]+)/*$") _ _) #t]
+    [_ #f]))
+
+(define (github-user+repo s)
+  (unless (github-source? s) (error 'github-user+repo "Expected github package-source: ~v" s))
+  (match (regexp-match "^([^/]+)/([^/]+)/*$" (git-source-repo s))
+    [(list _ user repo) (values user repo)]
+    [#f (error 'github-user+repo "Invalid github repo path: ~v" (git-source-repo s))]))
+
+(module+ test
+  (require rackunit)
+
+  (check-equal? (string->package-source "https://github.com/user/repo")
+                (url-source "https://github.com/user/repo"))
+  (check-equal? (string->package-source "http://example.com/some/path/to/package.zip")
+                (url-source "http://example.com/some/path/to/package.zip"))
+
+  (check-equal? (string->package-source "git://github.com/user/repo")
+                (git-source "github.com" #f "user/repo" "master" ""))
+  (check-equal? (string->package-source "git://github.com/user/repo#master")
+                (git-source "github.com" #f "user/repo" "master" ""))
+  (check-equal? (string->package-source "git://github.com/user/repo?path=/subdir1/subdir2#master")
+                (git-source "github.com" #f "user/repo" "master" "subdir1/subdir2"))
+  (check-equal? (string->package-source "git://github.com/user/repo?path=subdir1/subdir2#master")
+                (git-source "github.com" #f "user/repo" "master" "subdir1/subdir2"))
+  (check-equal? (string->package-source "git://github.com/user/repo?path=%2fsubdir1%2fsubdir2#master")
+                (git-source "github.com" #f "user/repo" "master" "subdir1/subdir2"))
+  (check-equal? (string->package-source "git://github.com/user/repo?path=subdir1%2fsubdir2#master")
+                (git-source "github.com" #f "user/repo" "master" "subdir1/subdir2"))
+  (check-equal? (string->package-source "git://github.com/user/repo#otherbranch")
+                (git-source "github.com" #f "user/repo" "otherbranch" ""))
+  (check-equal? (string->package-source "git://github.com/user/repo?path=/subdir1/subdir2#otherbranch")
+                (git-source "github.com" #f "user/repo" "otherbranch" "subdir1/subdir2"))
+  (check-equal? (string->package-source "git://github.com/user/repo?path=subdir1/subdir2#otherbranch")
+                (git-source "github.com" #f "user/repo" "otherbranch" "subdir1/subdir2"))
+  (check-equal? (string->package-source "git://github.com/user/repo?path=%2fsubdir1%2fsubdir2#otherbranch")
+                (git-source "github.com" #f "user/repo" "otherbranch" "subdir1/subdir2"))
+  (check-equal? (string->package-source "git://github.com/user/repo?path=subdir1%2fsubdir2#otherbranch")
+                (git-source "github.com" #f "user/repo" "otherbranch" "subdir1/subdir2"))
+
+  (check-exn #px"Invalid github url"
+             (lambda () (string->package-source "github://github.com/user/")))
+
+  (check-equal? (string->package-source "github://github.com/user/repo")
+                (git-source "github.com" #f "user/repo" "master" ""))
+  (check-equal? (string->package-source "github://github.com/user/repo/")
+                (git-source "github.com" #f "user/repo" "master" ""))
+  (check-equal? (string->package-source "github://github.com/user/repo/master")
+                (git-source "github.com" #f "user/repo" "master" ""))
+  (check-equal? (string->package-source "github://github.com/user/repo/master/")
+                (git-source "github.com" #f "user/repo" "master" ""))
+  (check-equal? (string->package-source "github://github.com/user/repo/master/subdir1/subdir2")
+                (git-source "github.com" #f "user/repo" "master" "subdir1/subdir2"))
+  (check-equal? (string->package-source "github://github.com/user/repo/otherbranch")
+                (git-source "github.com" #f "user/repo" "otherbranch" ""))
+  (check-equal? (string->package-source "github://github.com/user/repo/otherbranch/")
+                (git-source "github.com" #f "user/repo" "otherbranch" ""))
+  (check-equal? (string->package-source "github://github.com/user/repo/otherbranch/subdir1/subdir2")
+                (git-source "github.com" #f "user/repo" "otherbranch" "subdir1/subdir2"))
+
+  (check-equal? (package-source->string
+                 (git-source "github.com" #f "user/repo" "master" "subdir1/subdir2"))
+                "git://github.com/user/repo?path=subdir1%2Fsubdir2#master")
+  (check-equal? (package-source->string
+                 (git-source "github.com" #f "user/repo" "otherbranch" "subdir1/subdir2"))
+                "git://github.com/user/repo?path=subdir1%2Fsubdir2#otherbranch")
+
+  (define (roundtrip str)
+    (check-equal? (package-source->string (string->package-source str)) str))
+
+  (roundtrip "https://github.com/user/repo")
+  (roundtrip "http://example.com/some/path/to/package.zip")
+  (roundtrip "git://github.com/user/repo#master")
+  (roundtrip "git://github.com/user/repo#otherbranch")
+
+  (check-equal? (github-source? (string->package-source "github://github.com/user/repo")) #t)
+  (check-equal? (github-source? (string->package-source "github://github.com/user/repo/master")) #t)
+  (check-equal? (github-source? (string->package-source "github://github.com/user/repo/master/subdir")) #t)
+
+  (check-equal? (github-source? (string->package-source "git://github.com/user/repo")) #t)
+  (check-equal? (github-source? (string->package-source "git://github.com/user/repo#master")) #t)
+  (check-equal? (github-source? (string->package-source "git://github.com/user/repo?path=subdir#master")) #t)
+
+  (check-equal? (github-source? (string->package-source "git://github.com/user/repo/more")) #f)
+  (check-equal? (github-source? (string->package-source "git://github.com/user/repo/more#master")) #f)
+  (check-equal? (github-source? (string->package-source "git://github.com/user/repo/more?path=subdir#master")) #f)
+
+  (check-equal? (github-source? (string->package-source "git://github.com/user")) #f)
+  (check-equal? (github-source? (string->package-source "git://github.com/user#master")) #f)
+  (check-equal? (github-source? (string->package-source "git://github.com/user?path=subdir#master")) #f)
+
+  (check-equal? (github-source? (string->package-source "git://example.com/user/repo")) #f)
+  (check-equal? (github-source? (string->package-source "git://example.com/user/repo#master")) #f)
+  (check-equal? (github-source? (string->package-source "git://example.com/user/repo?path=subdir#master")) #f)
+
+  (define (extract-user+repo str)
+    (define-values (user repo) (github-user+repo (string->package-source str)))
+    (list user repo))
+
+  (check-equal? (extract-user+repo "github://github.com/user/repo") (list "user" "repo"))
+  (check-equal? (extract-user+repo "github://github.com/user/repo/master") (list "user" "repo"))
+  (check-equal? (extract-user+repo "github://github.com/user/repo/master/subdir") (list "user" "repo"))
+  (check-equal? (extract-user+repo "git://github.com/user/repo") (list "user" "repo"))
+  (check-equal? (extract-user+repo "git://github.com/user/repo#master") (list "user" "repo"))
+  (check-equal? (extract-user+repo "git://github.com/user/repo?path=subdir#master") (list "user" "repo"))
+  )
diff --git a/src/package-catalog/structs.rkt b/src/package-catalog/structs.rkt
new file mode 100644
index 0000000..87f6886
--- /dev/null
+++ b/src/package-catalog/structs.rkt
@@ -0,0 +1,269 @@
+#lang racket/base
+
+(provide (struct-out package)
+         package-author
+         serialize-package
+         deserialize-package
+
+         (struct-out computed-info)
+         serialize-computed-info
+         deserialize-computed-info
+
+         (struct-out github-info)
+         serialize-github-info
+         deserialize-github-info)
+
+(require racket/set)
+(require racket/match)
+(require (only-in racket/string string-split string-join))
+(require "source.rkt")
+
+;; A Time here is milliseconds-since-epoch - e.g. a result from
+;; (current-inexact-milliseconds).
+
+(define package-format-version 0) ;; IMPORTANT - UPDATE THIS AND CHANGE SERIALIZATION
+                                  ;; WHENEVER THE STRUCT DEFINITION FOR package CHANGES
+(struct package (name ;; String
+                 source ;; PackageSource
+                 description ;; String
+                 tags ;; (Listof String)
+                 authors ;; (Listof String)
+                 versions ;; (HashTable String PackageSource)
+                 ring ;; Nat
+                 last-edit ;; Time
+                 )
+        #:prefab)
+
+(define (package-author p)
+  (string-join (package-authors p) " "))
+
+(define computed-info-format-version 0) ;; IMPORTANT - UPDATE THIS AND CHANGE SERIALIZATION
+                                        ;; WHENEVER THE STRUCT DEFINITION FOR computed-info CHANGES
+(struct computed-info (package-name ;; String
+                       last-updated ;; Time, most recent change to package source
+                       last-checked ;; Time, when package source was most recently checked
+                       checksums ;; (HashTable String String), including "default" key
+                       checksum-errors ;; (HashTable String String), including "default" key
+                       github-info ;; GithubInfo or #f
+                       declared-conflicts ;; (Setof String), package names
+                       modules ;; (Listof ModulePath)
+                       dependencies ;; (Listof String), package names
+                       )
+        #:prefab)
+
+(define github-info-format-version 0) ;; IMPORTANT - UPDATE THIS AND CHANGE SERIALIZATION
+                                      ;; WHENEVER THE STRUCT DEFINITION FOR github-info CHANGES
+(struct github-info (readme-exists? ;; Boolean
+                     )
+        #:prefab)
+
+;;---------------------------------------------------------------------------
+;; This is the kind of stupid repetitive code our struct system should
+;; allow us to automate.
+
+(define (serialize-package p)
+  (match-define (package name source description tags authors versions ring last-edit) p)
+  (list 'package package-format-version
+        (hash 'name name
+              'source (package-source->string source)
+              'description description
+              'tags tags
+              'authors authors
+              'versions (for/hash [((version source) (in-hash versions))]
+                          (values version (package-source->string source)))
+              'ring ring
+              'last-edit last-edit)))
+
+(define (deserialize-package p)
+  (match p
+    [(? hash?)
+     (package (hash-ref p 'name)
+              (string->package-source (hash-ref p 'source))
+              (hash-ref p 'description "")
+              (hash-ref p 'tags '())
+              (string-split (hash-ref p 'author ""))
+              (for/hash [((version fields) (in-hash (hash-ref p 'versions (hash))))]
+                (values version (string->package-source (hash-ref fields 'source))))
+              (hash-ref p 'ring 2)
+              (hash-ref p 'last-edit 0))]
+    [(list 'package 0
+           (hash-table ['name (? string? name)]
+                       ['source (? string? source0)]
+                       ['description (? string? description)]
+                       ['tags (and (list (? string?) ...) tags)]
+                       ['authors (and (list (? string?) ...) authors)]
+                       ['versions versions0]
+                       ['ring (? number? ring)]
+                       ['last-edit (? number? last-edit)]))
+     (define source (string->package-source source0))
+     (define versions (for/hash [((version source) (in-hash versions0))]
+                        (values version (string->package-source source))))
+     (package name source description tags authors versions ring last-edit)]
+    [_
+     (error 'deserialize-package "Unrecognized serialized package: ~v" p)]))
+
+(define (serialize-computed-info ci)
+  (match-define (computed-info package-name
+                               last-updated
+                               last-checked
+                               checksums
+                               checksum-errors
+                               github-info
+                               declared-conflicts
+                               modules
+                               dependencies)
+                ci)
+  (list 'computed-info computed-info-format-version
+        (hash 'package-name package-name
+              'last-updated last-updated
+              'last-checked last-checked
+              'checksums checksums
+              'checksum-errors checksum-errors
+              'github-info (and github-info (serialize-github-info github-info))
+              'declared-conflicts declared-conflicts
+              'modules modules
+              'dependencies dependencies)))
+
+(define (deserialize-computed-info ci)
+  (match ci
+    [(? hash?)
+     (computed-info (hash-ref ci 'name)
+                    (hash-ref ci 'last-updated 0)
+                    (hash-ref ci 'last-checked 0)
+                    (let ((cs (for/hash [((v fs) (in-hash (hash-ref ci 'versions (hash))))
+                                         #:when (hash-has-key? fs 'checksum)]
+                                (values v (hash-ref fs 'checksum)))))
+                      (if (hash-has-key? ci 'checksum)
+                          (hash-set cs "default" (hash-ref ci 'checksum))
+                          cs))
+                    (let ((err (hash-ref ci 'checksum-error #f)))
+                      (if err
+                          (hash "default" err)
+                          (hash)))
+                    #f
+                    (list->set (hash-ref ci 'conflicts '()))
+                    (hash-ref ci 'modules '())
+                    (hash-ref ci 'dependencies '()))]
+    [(list 'computed-info 0
+           (hash-table ['package-name (? string? package-name)]
+                       ['last-updated (? number? last-updated)]
+                       ['last-checked (? number? last-checked)]
+                       ['checksums checksums]
+                       ['checksum-errors checksum-errors]
+                       ['github-info github-info0]
+                       ['declared-conflicts declared-conflicts]
+                       ['modules (and (list (? module-path?) ...) modules)]
+                       ['dependencies (and (list (? string?) ...) dependencies)]))
+     (define github-info (and github-info0 (deserialize-github-info github-info0)))
+     (computed-info package-name
+                    last-updated
+                    last-checked
+                    checksums
+                    checksum-errors
+                    github-info
+                    declared-conflicts
+                    modules
+                    dependencies)]
+    [_
+     (error 'deserialize-computed-info "Unrecognized serialized computed-info: ~v" ci)]))
+
+(define (serialize-github-info gi)
+  (match-define (github-info readme-exists?) gi)
+  (list 'github-info github-info-format-version
+        (hash 'readme-exists? readme-exists?)))
+
+(define (deserialize-github-info gi)
+  (match gi
+    [(list 'github-info 0
+           (hash-table ['readme-exists? readme-exists?]))
+     (github-info readme-exists?)]
+    [_
+     (error 'deserialize-github-info "Unrecognized serialized github-info: ~v" gi)]))
+
+;;---------------------------------------------------------------------------
+
+(module+ test
+  (require rackunit)
+
+  (define empty-zip "http://racket-packages.s3-us-west-2.amazonaws.com/pkgs/empty.zip")
+  (define empty-zip-checksum "9f098dddde7f217879070816090c1e8e74d49432")
+
+  (define xrepl-lib-hash
+    #hash((name . "xrepl-lib")
+          (source . "git://github.com/racket/xrepl/?path=xrepl-lib")
+          (author . "eli@racket-lang.org")
+          (last-updated . 1417912075)
+          (last-edit . 1417659583)
+          (last-checked . 1421095102)
+          (versions
+           . #hash(("5.3.5"
+                    . #hash((source
+                             . "http://racket-packages.s3-us-west-2.amazonaws.com/pkgs/empty.zip")
+                            (checksum . "9f098dddde7f217879070816090c1e8e74d49432")))
+                   ("5.3.4"
+                    . #hash((source
+                             . "http://racket-packages.s3-us-west-2.amazonaws.com/pkgs/empty.zip")
+                            (checksum . "9f098dddde7f217879070816090c1e8e74d49432")))
+                   ("5.3.6"
+                    . #hash((source
+                             . "http://racket-packages.s3-us-west-2.amazonaws.com/pkgs/empty.zip")
+                            (checksum . "9f098dddde7f217879070816090c1e8e74d49432")))))
+          (tags . ("main-distribution"))
+          (checksum-error . #f)
+          (ring . 0)
+          (checksum . "c88f8430b054d8a207a95acb0d1de0efece33510")
+          (description . "implementation (no documentation) part of \"xrepl\"")
+          (modules . ((lib "xrepl/saved-values.rkt")
+                      (lib "xrepl/xrepl.rkt")
+                      (lib "xrepl/main.rkt")))
+          (dependencies . ("base" "readline-lib" "scribble-text-lib"))
+          (conflicts . ())))
+
+  (define xrepl-lib (package "xrepl-lib"
+                             (git-source "github.com"
+                                         #f
+                                         "racket/xrepl"
+                                         "master"
+                                         "xrepl-lib")
+                             "implementation (no documentation) part of \"xrepl\""
+                             '("main-distribution")
+                             '("eli@racket-lang.org")
+                             (hash "5.3.4" (url-source empty-zip)
+                                   "5.3.5" (url-source empty-zip)
+                                   "5.3.6" (url-source empty-zip))
+                             0
+                             1417659583))
+
+  (define xrepl-lib-info (computed-info "xrepl-lib"
+                                        1417912075
+                                        1421095102
+                                        (hash "5.3.4" empty-zip-checksum
+                                              "5.3.5" empty-zip-checksum
+                                              "5.3.6" empty-zip-checksum
+                                              "default" "c88f8430b054d8a207a95acb0d1de0efece33510")
+                                        (hash)
+                                        #f
+                                        (set)
+                                        (list '(lib "xrepl/saved-values.rkt")
+                                              '(lib "xrepl/xrepl.rkt")
+                                              '(lib "xrepl/main.rkt"))
+                                        (list "base" "readline-lib" "scribble-text-lib")))
+
+  (check-equal? (deserialize-package xrepl-lib-hash) xrepl-lib)
+  (check-equal? (serialize-package xrepl-lib)
+                (list 'package package-format-version
+                      (hash 'name "xrepl-lib"
+                            'source "git://github.com/racket/xrepl?path=xrepl-lib#master"
+                            'tags '("main-distribution")
+                            'description "implementation (no documentation) part of \"xrepl\""
+                            'last-edit 1417659583
+                            'versions (hash "5.3.4" empty-zip
+                                            "5.3.5" empty-zip
+                                            "5.3.6" empty-zip)
+                            'ring 0
+                            'authors '("eli@racket-lang.org"))))
+  (check-equal? (deserialize-package (serialize-package xrepl-lib)) xrepl-lib)
+
+  (check-equal? (deserialize-computed-info xrepl-lib-hash) xrepl-lib-info)
+  (check-equal? (deserialize-computed-info (serialize-computed-info xrepl-lib-info)) xrepl-lib-info)
+  )