README.md

@@ -231,7 +231,7 @@ image, `make run` builds it and runs it on port 8080.
 | `PORT`                 | `8080`               | HTTP listen port                                                                                         |
 | `DATA_DIR`             | `./data/reports`     | Directory for compressed reports                                                                         |
 | `DATA_DIR_MAX_BYTES`   | `1073741824` (1 GiB) | Most bytes of report files kept in `DATA_DIR`, oldest deleted first; see [Report limits](#report-limits) |
-| `DEBUG`                | `false`              | Enable debug logging                                                                                     |
+| `DEBUG`                | empty                | Debug logging; any non-empty value, `false` and `0` included, turns it on                                |
 | `TRUSTED_PROXIES`      | RFC 1918 ranges      | Comma-separated CIDRs whose `X-Forwarded-For` / `X-Real-IP` headers are trusted for client IP resolution |
 | `REPORTS_PER_MINUTE`   | `60`                 | Reports each client address may send a minute; see [Report limits](#report-limits)                       |
 | `CORS_ALLOWED_ORIGINS` | empty                | Comma-separated origins whose pages may call the API; see [CORS](#cors)                                  |
@@ -254,10 +254,10 @@ an entry that is not an address at all, such as `unknown`, the direct peer is
 used. `X-Real-IP` is read only when `X-Forwarded-For` is missing or empty. The
 container image does not use this default; see [Deployment](#deployment).
 
-A variable set to a value the server cannot use, such as `PORT=abc`,
-`DEBUG=maybe` or a `BIND_ADDRESS` that is not an IP address, stops it from
-starting, with an error naming the variable. An empty variable counts as unset,
-except `TRUSTED_PROXIES`.
+A variable set to a value the server cannot use, such as `PORT=abc` or a
+`BIND_ADDRESS` that is not an IP address, stops it from starting, with an error
+naming the variable. An empty variable counts as unset, except
+`TRUSTED_PROXIES`. No value of `DEBUG` stops the start.
 
 #### Report storage
 
@@ -520,7 +520,8 @@ What the [upaas](https://git.eeqj.de/sneak/upaas) app for netwatch needs:
       report files may take; the oldest are deleted to stay under it
     - `CORS_ALLOWED_ORIGINS`, default empty: other origins whose pages may call
       the API
-    - `DEBUG`, default `false`: debug logging
+    - `DEBUG`, default empty: debug logging; any non-empty value, `false` and
+      `0` included, turns it on
     - `DATA_DIR`, default `/data/reports`: the directory the reports are kept
       in: `/data` or a path below it, with no `.` or `..` part and no extra `/`.
       The container also stops if the path goes through a symbolic link that

TODO.md

@@ -21,6 +21,12 @@ Run `make frontend-viewport-test` in CI as its own step; it is not part of
 
 # Completed Steps
 
+- 2026-10-19: `DEBUG` unset or empty leaves debug logging off, and any other
+  value, `false` and `0` included, turns it on, as the code style guide says
+  ([#159](https://git.eeqj.de/sneak/netwatch/issues/159)). No value of it stops
+  the start any more; before, only `1`, `t`, `T`, `TRUE`, `true`, `True`, `0`,
+  `f`, `F`, `FALSE`, `false` and `False` were accepted. `README.md` no longer
+  gives `false` as its default
 - 2026-10-19: check builds keep Go's modules and compiled packages between runs
   ([#118](https://git.eeqj.de/sneak/netwatch/issues/118)), on sneak's rulings in
   [prompts#113](https://git.eeqj.de/sneak/prompts/issues/113) and

internal/config/config.go

@@ -41,7 +41,6 @@ var (
 		"must be an origin, scheme://host with an optional port",
 	)
 	errNotPort = errors.New("must be a port number, 1 to 65535")
-	errNotBool = errors.New("must be true or false")
 	errNotIP   = errors.New("must be an IP address, or empty")
 
 	errMetricsCredentials = errors.New(
@@ -101,7 +100,7 @@ func New(
 	viper.SetDefault("CORS_ALLOWED_ORIGINS", "")
 	viper.SetDefault("DATA_DIR", "./data/reports")
 	viper.SetDefault("DATA_DIR_MAX_BYTES", defaultDataDirMaxBytes)
-	viper.SetDefault("DEBUG", "false")
+	viper.SetDefault("DEBUG", "")
 	// An empty BIND_ADDRESS listens on every interface.
 	viper.SetDefault("BIND_ADDRESS", "")
 	viper.SetDefault("PORT", "8080")
@@ -120,19 +119,17 @@ func New(
 		}
 	}
 
-	// Read with strconv: viper's GetInt and GetBool would read a value
-	// they cannot parse as 0 or false instead of failing.
+	// Read with strconv: viper's GetInt would read a value it cannot
+	// parse as 0 instead of failing.
 	port, err := strconv.Atoi(viper.GetString("PORT"))
 	if err != nil || port < 1 || port > math.MaxUint16 {
 		return nil, fmt.Errorf("PORT %q: %w",
 			viper.GetString("PORT"), errNotPort)
 	}
 
-	debug, err := strconv.ParseBool(viper.GetString("DEBUG"))
-	if err != nil {
-		return nil, fmt.Errorf("DEBUG %q: %w",
-			viper.GetString("DEBUG"), errNotBool)
-	}
+	// Any non-empty value turns debug logging on, "false" and "0"
+	// included, as the code style guide says.
+	debug := viper.GetString("DEBUG") != ""
 
 	// An empty TRUSTED_PROXIES trusts no proxy, but viper reads an
 	// empty environment variable as unset and would give the default,
@@ -172,8 +169,8 @@ func New(
 }
 
 // check fails with an error naming the first setting here whose value
-// the server cannot use. New checks PORT and DEBUG as it reads them,
-// and the middleware checks TRUSTED_PROXIES as it parses it.
+// the server cannot use. New checks PORT as it reads it, and the
+// middleware checks TRUSTED_PROXIES as it parses it.
 func (s *Config) check() error {
 	// viper reads a value that is not a number as 0, so this also
 	// catches a mistyped setting.

internal/config/config_test.go

@@ -127,12 +127,52 @@ func TestPortMustBeAPortNumber(t *testing.T) {
 	}
 }
 
-// TestDebugMustBeTrueOrFalse: viper reads any other value, such as
-// "yes", as false.
-func TestDebugMustBeTrueOrFalse(t *testing.T) {
-	t.Setenv("DEBUG", "yes")
+// TestDebugIsOnForAnyNonEmptyValue: unset or empty, debug logging is
+// off; any other value turns it on, "false" and "0" included, and none
+// stops the start.
+func TestDebugIsOnForAnyNonEmptyValue(t *testing.T) {
+	for _, tc := range []struct {
+		name  string
+		value string
+		unset bool
+		want  bool
+	}{
+		{name: "unset", unset: true, want: false},
+		{name: "empty", value: "", want: false},
+		{name: "false", value: "false", want: true},
+		{name: "0", value: "0", want: true},
+		{name: "yes", value: "yes", want: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			// t.Setenv first, so the variable is put back as it was
+			// after the test.
+			t.Setenv("DEBUG", tc.value)
 
-	requireConfigError(t, "DEBUG")
+			if tc.unset {
+				err := os.Unsetenv("DEBUG")
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+
+			var cfg *config.Config
+
+			app := fx.New(
+				fx.NopLogger,
+				fx.Provide(globals.New, logger.New, config.New),
+				fx.Populate(&cfg),
+			)
+
+			err := app.Err()
+			if err != nil {
+				t.Fatalf("config error = %v", err)
+			}
+
+			if cfg.Debug != tc.want {
+				t.Fatalf("Debug = %t, want %t", cfg.Debug, tc.want)
+			}
+		})
+	}
 }
 
 // TestBindAddressMustBeAnIPAddress: a host name would be looked up