diff --git a/spec/bridge/README.md b/spec/bridge/README.md
index cad288ba..964fc225 100644
--- a/spec/bridge/README.md
+++ b/spec/bridge/README.md
@@ -149,6 +149,7 @@ be handed it, so nothing is skipped for being inconvenient, and the count is vis
 | utility       | what makes it worth porting                                       |
 | ------------- | ----------------------------------------------------------------- |
 | `isValidCnpj` | regular expressions, check digits, JavaScript's own type coercion |
+| `formatCnpj`  | a shared mask helper, and three options that interact             |
 
 ## Adding a utility
 
diff --git a/spec/bridge/conformance/cases/format-cnpj.ts b/spec/bridge/conformance/cases/format-cnpj.ts
new file mode 100644
index 00000000..6363e141
--- /dev/null
+++ b/spec/bridge/conformance/cases/format-cnpj.ts
@@ -0,0 +1,28 @@
+/**
+ * What `formatCnpj` is replayed with: the whole CNPJ corpus, under every option combination.
+ */
+import { type Recorder } from "../cases.ts";
+import { cnpjCorpus } from "./_cnpj-corpus.ts";
+
+const OPTIONS = [
+	undefined,
+	{ version: 2 },
+	{ pad: true },
+	{ obfuscate: true },
+	{ pad: true, version: 2 },
+	{ obfuscate: true, version: 2 },
+	{ obfuscate: true, pad: true },
+];
+
+export const recorder: Recorder = {
+	module: "format-cnpj",
+	inputs: (shipped) => {
+		const corpus = cnpjCorpus(shipped["generateCnpj"] as (version?: 1 | 2) => string);
+		const found: unknown[][] = [];
+
+		for (const input of corpus)
+			for (const options of OPTIONS) found.push(options === undefined ? [input] : [input, options]);
+
+		return found;
+	},
+};
diff --git a/spec/bridge/source/_internals/mask.ts b/spec/bridge/source/_internals/mask.ts
new file mode 100644
index 00000000..092e94f1
--- /dev/null
+++ b/spec/bridge/source/_internals/mask.ts
@@ -0,0 +1,56 @@
+/**
+ * Laying a value over a mask, which is what every `format*` utility does.
+ *
+ * The mask is a string: `0` is a slot the value fills, `*` is a slot the value fills and the
+ * mask hides, and anything else is a separator, written only while there is still value left
+ * to write.
+ */
+
+/**
+ * Lays a value over a pattern.
+ *
+ * @param {string} value - The sanitized value.
+ * @param {string} pattern - The mask.
+ * @param {boolean} pad - Whether to left pad the value with zeros up to the number of slots.
+ * @returns {string} The masked value, cut short where the value runs out.
+ */
+export const layout = (value: string, pattern: string, pad: boolean): string => {
+	let slots = 0;
+
+	for (let index = 0; index < pattern.length; index++) {
+		if (pattern.charCodeAt(index) === 48 || pattern.charCodeAt(index) === 42) {
+			slots += 1;
+		}
+	}
+
+	let padded = value;
+
+	if (pad) {
+		padded = value.padStart(slots, "0");
+	}
+
+	let formatted = "";
+	let cursor = 0;
+
+	for (let index = 0; index < pattern.length; index++) {
+		const slot = pattern.charCodeAt(index);
+
+		if (slot === 48 || slot === 42) {
+			if (cursor >= padded.length) {
+				return formatted;
+			}
+
+			if (slot === 42) {
+				formatted += "*";
+			} else {
+				formatted += padded.slice(cursor, cursor + 1);
+			}
+
+			cursor += 1;
+		} else if (cursor < padded.length) {
+			formatted += pattern.slice(index, index + 1);
+		}
+	}
+
+	return formatted;
+};
diff --git a/spec/bridge/source/format-cnpj.ts b/spec/bridge/source/format-cnpj.ts
new file mode 100644
index 00000000..104ee34a
--- /dev/null
+++ b/spec/bridge/source/format-cnpj.ts
@@ -0,0 +1,63 @@
+/**
+ * `formatCnpj`, written once.
+ *
+ * The boundary guards are the handwritten package's, not a tidier version of them: a nullish
+ * value answers the empty string, and a value the mask outruns is cut short rather than
+ * padded, because that is what the JavaScript this repository ships already does.
+ *
+ * @see Official: https://www.gov.br/receitafederal/pt-br/assuntos/orientacao-tributaria/cadastros/cnpj
+ * @see Official: https://www.gov.br/receitafederal/pt-br/acesso-a-informacao/acoes-e-programas/programas-e-atividades/cnpj-alfanumerico
+ */
+import { NON_ALPHANUMERIC, NON_DIGIT } from "./_internals/cnpj.ts";
+import { layout } from "./_internals/mask.ts";
+import { asString, isTruthy } from "./_std.ts";
+
+/** Options of `formatCnpj`. */
+export type FormatCnpjOptions = {
+	/** Whether to left pad the value with zeros up to the number of slots in the pattern (default: `false`). */
+	pad?: boolean;
+	/** Which CNPJ format to read: `1` numeric only, `2` alphanumeric (default: `1`). */
+	version?: 1 | 2;
+	/** Whether to hide the first 2 digits and the 2 check digits with `*` (default: `false`). */
+	obfuscate?: boolean;
+};
+
+const PATTERN = "00.000.000/0000-00";
+const OBFUSCATED_PATTERN = "**.000.000/0000-**";
+
+/**
+ * Formats a given CNPJ (Cadastro Nacional da Pessoa Jurídica) value.
+ *
+ * @param {string} value - The CNPJ value to be formatted.
+ * @param {FormatCnpjOptions} [options] - Optional configuration for formatting the CNPJ.
+ * @returns {string} The formatted CNPJ string in the pattern "00.000.000/0000-00".
+ *
+ * @example
+ * ```typescript
+ * formatCnpj("12345678000195"); // "12.345.678/0001-95"
+ * formatCnpj("12345678", { pad: true }); // "00.000.012/3456-78"
+ * formatCnpj("q0SLFMBD7VX439", { version: 2 }); // "Q0.SLF.MBD/7VX4-39"
+ * formatCnpj("12345678000195", { obfuscate: true }); // "**.345.678/0001-**"
+ * ```
+ */
+export const formatCnpj = (value: string | number, options?: FormatCnpjOptions): string => {
+	if (value === null || value === undefined) {
+		return "";
+	}
+
+	const text = asString(value);
+
+	let cleaned = text.replaceAll(NON_DIGIT, "");
+
+	if (options?.version === 2) {
+		cleaned = text.replaceAll(NON_ALPHANUMERIC, "").toUpperCase();
+	}
+
+	let pattern = PATTERN;
+
+	if (isTruthy(options?.obfuscate)) {
+		pattern = OBFUSCATED_PATTERN;
+	}
+
+	return layout(cleaned, pattern, isTruthy(options?.pad));
+};