diff --git a/CHANGELOG.md b/CHANGELOG.md
index cc2a9d9..74d3b46 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,12 @@ at boot. Entries start at 0.3.0.
 
 ## Unreleased
 
+### A malformed URL setting's boot error no longer prints the value
+
+When a URL setting such as `PLUGIN_DB_URL`, `PLUGIN_DB_ADMIN_URL` or `OTLP_ENDPOINT` can't be parsed,
+the boot error names the variable and not its value, so a DSN whose password breaks parsing doesn't
+put the password in the log.
+
 ### A secret plugin setting's bad value stays out of the boot error
 
 When a `secret` setting's value fails validation, the boot error no longer prints it, so a malformed
diff --git a/docs/reading-cost.md b/docs/reading-cost.md
index c3d477d..2e1aaa0 100644
--- a/docs/reading-cost.md
+++ b/docs/reading-cost.md
@@ -291,3 +291,16 @@ Read most (opens and searches):
 - `e2e-tests/full-flow.spec.ts` 1
 - `examples/plugins/admin/admin-users.test.ts` 1
 - `examples/plugins/admin/admin-users.ts` 1
+
+## Reading cost, chunk f0a49c300aac, finished 2026-10-31T12:47:27Z
+
+63526 new input tokens before the first commit.
+
+Read most (opens and searches):
+
+- `README.md` 4
+- `src/plugin-host/settings.test.ts` 3
+- `todo.md` 3
+- `CHANGELOG.md` 2
+- `src/plugin-host/settings.ts` 2
+- `AGENTS.md` 1
diff --git a/src/auth/bootstrap.test.ts b/src/auth/bootstrap.test.ts
index f57655b..5040804 100644
--- a/src/auth/bootstrap.test.ts
+++ b/src/auth/bootstrap.test.ts
@@ -181,6 +181,16 @@ test("provisioning still runs with nothing to provision, so orphans are reported
   assert.deepEqual(calls[0]?.pluginIds, []);
 });
 
+// The postgres driver rethrows a malformed DSN with the whole string on the error (`input`), so
+// the URL is checked here, before the driver sees it.
+test("a malformed PLUGIN_DB_ADMIN_URL is refused by name, never echoing the password", async () => {
+  const env = { PLUGIN_DB_ADMIN_URL: "postgres://admin:pa/ss@db:5432/plugins" };
+  await assert.rejects(
+    provisionPluginStorage(env, [storagePlugin("things")], SILENT, async () => ({ orphans: [], provisioned: [] })),
+    (err: Error) => err.message.includes("PLUGIN_DB_ADMIN_URL") && !err.message.includes("pa/ss"),
+  );
+});
+
 test("a plugin declaring storage without a provisioning DSN fails loud, naming the plugin", async () => {
   const { calls, provision } = recordingProvisioner();
   await assert.rejects(
diff --git a/src/auth/bootstrap.ts b/src/auth/bootstrap.ts
index 137ef59..2e3c732 100644
--- a/src/auth/bootstrap.ts
+++ b/src/auth/bootstrap.ts
@@ -8,7 +8,7 @@
 // Then prints a first-run banner; fails loud on any unexpected upstream error.
 import { existsSync, writeFileSync } from "node:fs";
 import { fileURLToPath } from "node:url";
-import { resolvePluginDbConnectionLimit, resolvePluginDbSecret } from "../config.ts";
+import { assertUrl, resolvePluginDbConnectionLimit, resolvePluginDbSecret } from "../config.ts";
 import { discoverPlugins } from "../plugin-host/discovery.ts";
 import { declaredPermissions, isValidPermissionName, type Plugin } from "../plugin-host/plugin.ts";
 import { provisionStorage } from "../plugin-host/storage-provisioning.ts";
@@ -179,6 +179,7 @@ export async function provisionPluginStorage(env: Env, plugins: Plugin[], log: L
   // Provisioned here, connected to from web: a different server means the role is created in one
   // place and looked for in another, surfacing inside a plugin as "password authentication failed".
   // Warned, not refused — web reaching a pooler that cannot run CREATE DATABASE is a legitimate split.
+  assertUrl("PLUGIN_DB_ADMIN_URL", adminUrl);
   const mismatch = serverMismatch(adminUrl, env["PLUGIN_DB_URL"]);
   if (mismatch) log.warn("PLUGIN_DB_ADMIN_URL and PLUGIN_DB_URL name different servers", { servers: mismatch });
   const result = await provision({
@@ -199,7 +200,7 @@ export async function provisionPluginStorage(env: Env, plugins: Plugin[], log: L
 export function serverMismatch(adminUrl: string, webUrl: string | undefined): string | null {
   if (!webUrl) return null;
   const [admin, web] = [safeHostPort(adminUrl), safeHostPort(webUrl)];
-  if (admin === null || web === null || admin === web) return null; // a malformed URL fails in config.ts
+  if (admin === null || web === null || admin === web) return null; // a malformed URL fails in assertUrl
   return `${admin} vs ${web}`;
 }
 
diff --git a/src/config.test.ts b/src/config.test.ts
index 62a00d5..dbd9b11 100644
--- a/src/config.test.ts
+++ b/src/config.test.ts
@@ -39,6 +39,29 @@ test("PLUGIN_DB_URL carrying credentials is refused, not silently overwritten",
   assert.equal(loadConfig({}).pluginDbUrl, undefined); // unset ⇒ storage off
 });
 
+// A DSN whose password breaks URL parsing (a bare "/") must not reach the boot error or the log.
+// The credential-bearing keys get their own value; the rest share the two readers, so one loop covers them.
+test("a malformed URL value is refused by naming the variable, never echoing the value", () => {
+  const bad: Record<string, string> = {
+    APP_URL: "https://acme:pa/ss@[host",
+    HYDRA_ADMIN_URL: "http://u:pa/ss@[hydra:4445",
+    JWKS_URL: "http://u:pa/ss@[jwks",
+    KETO_READ_URL: "http://u:pa/ss@[keto:4466",
+    KETO_WRITE_URL: "http://u:pa/ss@[keto:4467",
+    KRATOS_ADMIN_URL: "http://u:pa/ss@[kratos:4434",
+    KRATOS_PUBLIC_URL: "http://u:pa/ss@[kratos:4433",
+    OTLP_ENDPOINT: "http://otel:pa/ss@[collector:4318",
+    PLUGIN_DB_URL: "postgres://admin:pa/ss@db:5432/plugins",
+  };
+  for (const [key, value] of Object.entries(bad)) {
+    assert.throws(
+      () => loadConfig({ [key]: value }),
+      (err: Error) => err.message.includes(key) && !err.message.includes("pa/ss") && !err.message.includes(value),
+      key,
+    );
+  }
+});
+
 test("the per-role connection ceiling defaults to 10 and rejects nonsense", () => {
   assert.equal(resolvePluginDbConnectionLimit({}), 10);
   assert.equal(resolvePluginDbConnectionLimit({ PLUGIN_DB_CONNECTION_LIMIT: "25" }), 25);
diff --git a/src/config.ts b/src/config.ts
index dcceb5d..bfb81a9 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -98,26 +98,28 @@ function readEnum<T extends string>(env: Env, key: string, allowed: readonly T[]
   throw new Error(`config: ${key} must be one of ${allowed.join(", ")}, got "${value}"`);
 }
 
-// An optional absolute URL: unset/empty ⇒ undefined; a set-but-malformed value fails at boot.
-function readOptionalUrl(env: Env, key: string): string | undefined {
-  const value = env[key] || undefined;
-  if (value === undefined) return undefined;
+// Never echoes the value: a DSN whose password breaks URL parsing (a bare "/") would put the
+// password in the boot error and the log. bootstrap uses it too, before the postgres driver, which
+// rethrows a malformed DSN with the whole string attached.
+export function assertUrl(key: string, value: string): void {
   try {
     new URL(value);
   } catch {
-    throw new Error(`config: ${key} is not a valid URL: ${value}`);
+    throw new Error(`config: ${key} must be an absolute URL (its value is not shown; percent-encode special characters in a password)`);
   }
+}
+
+// An optional absolute URL: unset/empty ⇒ undefined; a set-but-malformed value fails at boot.
+function readOptionalUrl(env: Env, key: string): string | undefined {
+  const value = env[key] || undefined;
+  if (value !== undefined) assertUrl(key, value);
   return value;
 }
 
 // An absolute URL: defaults to the Ory service; validated so a typo fails at boot.
 function readUrl(env: Env, key: string, devDefault: string): string {
   const value = env[key] ?? devDefault;
-  try {
-    new URL(value);
-  } catch {
-    throw new Error(`config: ${key} is not a valid URL: ${value}`);
-  }
+  assertUrl(key, value);
   return value;
 }
 
diff --git a/todo.md b/todo.md
index c52b36d..9426548 100644
--- a/todo.md
+++ b/todo.md
@@ -12,7 +12,6 @@
 
 | ID | Release | Blocked by | Exempt | Item | L | E | I | R | S | Moves | Score |
 |---|---|---|---|---|---|---|---|---|---|---|---|
-| 55 | 0.4.21 |  | security | **Keep a URL config value out of the boot error that rejects it.** | 1 | 1 | 4 | 5 | 2 |  | 0.0 |
 | 19 | 0.5.0 |  | question | **Run the documented Docker commands on macOS and fix whatever misbehaves.** | 2 | 2 | 1 | 3 | 3 | 1 by 3 | 3.3 |
 | 16 | 0.5.0 |  | question | **Decide whether the single Keto `Resource` namespace splits into per-domain namespaces.** | 3 | 2 | 3 | 6 | 6 | 7 by 2 | 0.5 |
 | 48 | 0.5.0 |  |  | **Correct the Keto tuple in the `login.ts` and `bootstrap.ts` comments to the `granted` relation the code writes.** | 1 | 1 | 1 | 1 | 1 | code health by 4 | 28.7 |
@@ -34,20 +33,6 @@
 
 ## Details
 
-### 55. Keep a URL config value out of the boot error that rejects it.
-
-`readOptionalUrl` and `readUrl` in `src/config.ts` throw `config: ${key} is not a valid URL: ${value}`,
-so a malformed value reaches the boot error and the log. A DSN whose password breaks parsing, such as
-`postgres://admin:pa/ss@db:5432/plugins`, leaks that password. The keys that can carry credentials:
-`PLUGIN_DB_URL` (`readCredentiallessUrl` refuses userinfo only after `readOptionalUrl` has parsed it,
-so a pasted admin DSN that fails to parse is echoed), and `OTLP_ENDPOINT`, whose collector URL may
-embed basic-auth userinfo. The other URL keys, `APP_URL`, `HYDRA_ADMIN_URL`, `JWKS_URL`,
-`KETO_READ_URL`, `KETO_WRITE_URL`, `KRATOS_ADMIN_URL` and `KRATOS_PUBLIC_URL`, pass through the same
-two readers, so the fix covers them too. Name the variable and what it accepts, never the value, and
-add a test per credential-bearing key. The other readers in `config.ts` echo only non-credential
-values. `PLUGIN_DB_ADMIN_URL` isn't read in `config.ts`: `bootstrap.ts` hands it straight to
-`postgres()`. Check whether the driver echoes a malformed one.
-
 ### 19. Run the documented Docker commands on macOS and fix whatever misbehaves.
 
 Needs a Mac. Two suspects, both from `--user "$(id -u):$(id -g)"`: a macOS `id -g` is `20`, which is