diff --git a/ADR.md b/ADR.md
index b1d3fc5..cd33292 100644
--- a/ADR.md
+++ b/ADR.md
@@ -76,3 +76,22 @@ Consequences: Without the key no secret can be saved or used, and a changed key
 secrets unusable until they are entered again. SHA-256 does not slow down guessing a weak key, so
 the key has to be long and random. Anyone who reaches the routes can replace credentials, as the
 applications have no authentication.
+
+## ADR-4: The key of a credential store is a path, so related stores share one object
+
+Status: Accepted
+
+Context: sql-query-webui keeps connection profiles of PostgreSQL and of SQL Server. As stores of
+top-level keys, the keys have to carry the kind in their names, and a key such as `connections`
+does not say which kind it holds once there are several.
+
+Decision: The key of a store is a key of `config.json` or a path of keys separated by dots, such
+as `connections.pg` and `connections.mssql`. The store reads the list at the path, reports its
+problems by `<path>.<index>.<field>`, and a write sets the list at the path, creating the objects
+of the path that are missing, or are not objects, and keeping their other keys, so stores of one
+object can be written one after the other. The kind stays the store's, not a field of an entry
+(ADR-3).
+
+Consequences: A key of `config.json` holding a dot cannot be the key of a store. A single key
+reads and writes as before, so applications of one-key stores need no change. The application
+checks the object of a path, such as the keys it allows in it, itself.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index fa56d0d..7f0b41c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## 0.3.0
+
+feature: the key of a credential store may be a path of keys, so stores of several kinds share one object of config.json.
+
+- `CredentialStore.key` is a key of `config.json` or a path of keys separated by dots, such as
+  `connections.pg`; read, validate, write and `credentialValues` use the list at that path, and a
+  write creates the objects of the path that are missing and keeps their other keys.
+
 ## 0.2.1
 
 fix: a credential store holds credentials of one kind, without a kind field in its entries, and the dialog edits several stores in tabs.
diff --git a/README.md b/README.md
index 9ce6b06..2f783eb 100644
--- a/README.md
+++ b/README.md
@@ -124,7 +124,19 @@ saved or used; a secret encrypted with another key cannot be decrypted and has t
 again.
 
 `CredentialStore` describes a store: the path of `config.json`, the key, the kind, the reserved
-names and whether a missing `config.json` reads as `{}`.
+names and whether a missing `config.json` reads as `{}`. The key is a key of `config.json` or a
+path of keys separated by dots, such as `connections.pg`, for a list in nested objects; a write
+creates the objects of the path that are missing and keeps their other keys, so stores of several
+kinds can share one object:
+
+```json
+{
+  "connections": {
+    "pg": [{ "name": "state", "host": "db.example.com", "port": 5432, "...": "..." }],
+    "mssql": [{ "name": "warehouse", "host": "sql.example.com", "port": 1433, "...": "..." }]
+  }
+}
+```
 
 - `credentialProblems(value, store)`: the problems of the key's value by `<key>.<index>.<field>`,
   for the application's own check of `config.json`.
diff --git a/package-lock.json b/package-lock.json
index 0291af0..f6cfa93 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@koszewscy/sk-react-toolkit",
-  "version": "0.2.1",
+  "version": "0.3.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@koszewscy/sk-react-toolkit",
-      "version": "0.2.1",
+      "version": "0.3.0",
       "devDependencies": {
         "@emotion/react": "^11.14.0",
         "@emotion/styled": "^11.14.1",
diff --git a/package.json b/package.json
index 14d75a5..2162481 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@koszewscy/sk-react-toolkit",
-  "version": "0.2.1",
+  "version": "0.3.0",
   "description": "Shared code of the React and Fastify web applications: web components, server helpers and the Vite font plugin.",
   "private": true,
   "type": "module",
diff --git a/server/credentials.ts b/server/credentials.ts
index b6b09d7..91884f1 100644
--- a/server/credentials.ts
+++ b/server/credentials.ts
@@ -8,7 +8,8 @@ import { decrypt, encrypt, encryptionKey } from './secrets.ts'
 
 /**
  * A credential store: the list under key of config.json at configPath, every entry of the kind the application gives,
- * with the names reserved for its own credentials. With missingAsEmpty a missing config.json reads as {}, and the
+ * with the names reserved for its own credentials. key is a key of config.json or a path of keys separated by dots,
+ * such as connections.pg, for a list in nested objects. With missingAsEmpty a missing config.json reads as {}, and the
  * first write creates it.
  */
 export type CredentialStore = {
@@ -114,9 +115,30 @@ export function credentialProblems(entries: unknown, store: Pick<CredentialStore
   return problems
 }
 
+const isObject = (value: unknown): value is Record<string, unknown> => value !== null && typeof value === 'object' && !Array.isArray(value)
+
+/** The value of data at key, a key or a path of keys separated by dots; undefined when it is not there. */
+function valueAt(data: Record<string, unknown>, key: string): unknown {
+  return key.split('.').reduce<unknown>((value, part) => (isObject(value) ? value[part] : undefined), data)
+}
+
+/**
+ * data with value at key, a key or a path of keys separated by dots, after the other keys of its object; the objects
+ * of the path that are missing, or are not objects, are created, and their other keys kept.
+ */
+function withValue(data: Record<string, unknown>, key: string, value: unknown): Record<string, unknown> {
+  const [first, ...rest] = key.split('.')
+  if (rest.length > 0) {
+    return { ...data, [first]: withValue(isObject(data[first]) ? data[first] : {}, rest.join('.'), value) }
+  }
+  const others = { ...data }
+  delete others[first]
+  return { ...others, [first]: value }
+}
+
 /** The entries of the store's key in config.json; a value that is not a list reads as none. */
 function entriesOf(data: Record<string, unknown>, store: CredentialStore): Record<string, unknown>[] {
-  const entries = data[store.key]
+  const entries = valueAt(data, store.key)
   return Array.isArray(entries) ? entries.filter((entry) => entry !== null && typeof entry === 'object') : []
 }
 
@@ -185,7 +207,7 @@ function toEntries(profiles: CredentialProfile[], data: Record<string, unknown>,
  */
 export function credentialValues(store: CredentialStore, name: string): CredentialValues {
   const { data } = read(store)
-  const [problem] = Object.entries(credentialProblems(data[store.key], store))
+  const [problem] = Object.entries(credentialProblems(valueAt(data, store.key), store))
   if (problem !== undefined) {
     throw new HttpError(500, `${problem[0]} in ${store.configPath} ${problem[1]}.`)
   }
@@ -234,8 +256,8 @@ export function registerCredentialRoutes(app: FastifyInstance, store: Credential
   function problemsOf(value: CredentialProfile[], data: Record<string, unknown>): Record<string, string> {
     const problems: Record<string, string> = {}
     for (const [path, message] of Object.entries(credentialProblems(toEntries(value, data, store, () => 'new'), store))) {
-      const [, index, field] = path.split('.')
-      problems[field === undefined ? index ?? store.key : `${index}.${field}`] = `${field ?? 'The credential'} ${message}.`
+      const [index, field] = path.slice(store.key.length + 1).split('.')
+      problems[field === undefined ? index || store.key : `${index}.${field}`] = `${field ?? 'The credential'} ${message}.`
     }
     if (key() === null) {
       value.forEach((profile, index) => {
@@ -279,11 +301,9 @@ export function registerCredentialRoutes(app: FastifyInstance, store: Credential
       throw new HttpError(422, 'The credentials are not valid.', problems)
     }
     const sealing = key()!
-    const others = { ...file.data }
-    delete others[store.key]
     const entries = toEntries(request.body.value, file.data, store, (secret) => encrypt(secret, sealing))
     try {
-      writeFileSync(store.configPath, `${JSON.stringify({ ...others, [store.key]: entries }, null, 2)}\n`)
+      writeFileSync(store.configPath, `${JSON.stringify(withValue(file.data, store.key, entries), null, 2)}\n`)
     } catch (error) {
       throw new HttpError(500, `${store.configPath} cannot be written: ${(error as Error).message}`)
     }