diff --git a/modules/netcheck/cmd/netcheck/checks.go b/modules/netcheck/cmd/netcheck/checks.go
new file mode 100644
index 0000000..152b6e4
--- /dev/null
+++ b/modules/netcheck/cmd/netcheck/checks.go
@@ -0,0 +1,173 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"math"
+	"net"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Bounds on what a caller may ask: a check is a probe, never a wait anyone can make long.
+const (
+	DefaultTimeout = 3 * time.Second
+	MostTimeout    = 30 * time.Second
+)
+
+// TCPResult is what netcheck_tcp answers.
+type TCPResult struct {
+	Host      string `json:"host"`
+	Port      int    `json:"port"`
+	Address   string `json:"address,omitempty"`
+	Reachable bool   `json:"reachable"`
+	ElapsedMS int64  `json:"elapsed_ms"`
+	Error     string `json:"error,omitempty"`
+}
+
+// CheckTCP opens one TCP connection and closes it, sending nothing. A port that refuses or a host
+// that does not answer is a result, not a failure of the tool; only a malformed question is.
+func CheckTCP(host string, port int, timeout time.Duration) (TCPResult, error) {
+	if port < 1 || port > 65535 {
+		return TCPResult{}, fmt.Errorf("port %d is not a TCP port (1-65535)", port)
+	}
+	out := TCPResult{Host: host, Port: port}
+	start := time.Now()
+	conn, err := net.DialTimeout("tcp", net.JoinHostPort(host, strconv.Itoa(port)), timeout)
+	out.ElapsedMS = time.Since(start).Milliseconds()
+	if err != nil {
+		out.Error = err.Error()
+		return out, nil
+	}
+	out.Address = conn.RemoteAddr().String()
+	out.Reachable = true
+	_ = conn.Close()
+	return out, nil
+}
+
+// DNSResult is what netcheck_dns answers.
+type DNSResult struct {
+	Name      string   `json:"name"`
+	Type      string   `json:"type"`
+	Answers   []string `json:"answers"`
+	ElapsedMS int64    `json:"elapsed_ms"`
+	Error     string   `json:"error,omitempty"`
+}
+
+// DNSTypes are the record types netcheck_dns looks up.
+var DNSTypes = []string{"A", "AAAA", "CNAME", "TXT", "MX"}
+
+// CheckDNS looks a name up with the machine's resolver. Built without cgo, Go's own resolver reads
+// the machine's /etc/resolv.conf and /etc/hosts, which is the resolver this machine's programs use.
+// A name that does not resolve is a result with its error; an unknown type is refused.
+func CheckDNS(name, kind string, timeout time.Duration) (DNSResult, error) {
+	kind = strings.ToUpper(strings.TrimSpace(kind))
+	if kind == "" {
+		kind = "A"
+	}
+	known := false
+	for _, t := range DNSTypes {
+		known = known || t == kind
+	}
+	if !known {
+		return DNSResult{}, fmt.Errorf("type %q is not one netcheck_dns looks up (%s)", kind, strings.Join(DNSTypes, ", "))
+	}
+	out := DNSResult{Name: name, Type: kind, Answers: []string{}}
+	ctx, cancel := context.WithTimeout(context.Background(), timeout)
+	defer cancel()
+	r := net.DefaultResolver
+	start := time.Now()
+	var err error
+	switch kind {
+	case "A", "AAAA":
+		network := "ip4"
+		if kind == "AAAA" {
+			network = "ip6"
+		}
+		var ips []net.IP
+		if ips, err = r.LookupIP(ctx, network, name); err == nil {
+			for _, ip := range ips {
+				out.Answers = append(out.Answers, ip.String())
+			}
+		}
+	case "CNAME":
+		var cname string
+		if cname, err = r.LookupCNAME(ctx, name); err == nil {
+			out.Answers = append(out.Answers, cname)
+		}
+	case "TXT":
+		var txts []string
+		if txts, err = r.LookupTXT(ctx, name); err == nil {
+			out.Answers = append(out.Answers, txts...)
+		}
+	case "MX":
+		var mxs []*net.MX
+		if mxs, err = r.LookupMX(ctx, name); err == nil {
+			for _, mx := range mxs {
+				out.Answers = append(out.Answers, fmt.Sprintf("%d %s", mx.Pref, mx.Host))
+			}
+		}
+	}
+	out.ElapsedMS = time.Since(start).Milliseconds()
+	if err != nil {
+		out.Error = err.Error()
+	}
+	if kind != "MX" {
+		sort.Strings(out.Answers)
+	}
+	return out, nil
+}
+
+// text is a required string argument.
+func text(args map[string]any, key string) (string, error) {
+	s, _ := args[key].(string)
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return "", fmt.Errorf("%s is required", key)
+	}
+	return s, nil
+}
+
+// whole is an integer argument, given as a JSON number or a numeric string; fallback when absent.
+func whole(args map[string]any, key string, fallback int) (int, error) {
+	v, given := args[key]
+	if !given || v == nil {
+		if fallback == 0 {
+			return 0, fmt.Errorf("%s is required", key)
+		}
+		return fallback, nil
+	}
+	switch n := v.(type) {
+	case float64:
+		if n != math.Trunc(n) {
+			return 0, fmt.Errorf("%s must be a whole number, not %v", key, n)
+		}
+		return int(n), nil
+	case string:
+		i, err := strconv.Atoi(strings.TrimSpace(n))
+		if err != nil {
+			return 0, fmt.Errorf("%s must be a whole number, not %q", key, n)
+		}
+		return i, nil
+	}
+	return 0, errors.New(key + " must be a whole number")
+}
+
+// timeoutOf is timeout_ms, defaulted and bounded.
+func timeoutOf(args map[string]any) (time.Duration, error) {
+	ms, err := whole(args, "timeout_ms", int(DefaultTimeout/time.Millisecond))
+	if err != nil {
+		return 0, err
+	}
+	if ms < 1 {
+		return 0, fmt.Errorf("timeout_ms must be at least 1, not %d", ms)
+	}
+	d := time.Duration(ms) * time.Millisecond
+	if d > MostTimeout {
+		d = MostTimeout
+	}
+	return d, nil
+}
diff --git a/modules/netcheck/cmd/netcheck/checks_test.go b/modules/netcheck/cmd/netcheck/checks_test.go
new file mode 100644
index 0000000..8e2af86
--- /dev/null
+++ b/modules/netcheck/cmd/netcheck/checks_test.go
@@ -0,0 +1,68 @@
+package main
+
+import (
+	"net"
+	"testing"
+	"time"
+)
+
+func TestATCPPortThatListensIsReachableAndOneThatDoesNotIsNot(t *testing.T) {
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	port := l.Addr().(*net.TCPAddr).Port
+	got, err := CheckTCP("127.0.0.1", port, time.Second)
+	if err != nil || !got.Reachable || got.Error != "" {
+		t.Fatalf("a listening port: %+v, %v", got, err)
+	}
+	l.Close()
+	got, err = CheckTCP("127.0.0.1", port, time.Second)
+	if err != nil || got.Reachable || got.Error == "" {
+		t.Fatalf("a closed port is reported as a result with its error, not a failure: %+v, %v", got, err)
+	}
+}
+
+func TestAPortOutsideTheRangeIsRefused(t *testing.T) {
+	for _, p := range []int{0, -1, 65536} {
+		if _, err := CheckTCP("127.0.0.1", p, time.Second); err == nil {
+			t.Errorf("port %d was accepted", p)
+		}
+	}
+}
+
+func TestDNSAnswersFromTheMachinesResolverAndRefusesAnUnknownType(t *testing.T) {
+	got, err := CheckDNS("localhost", "a", time.Second)
+	if err != nil || got.Type != "A" || len(got.Answers) == 0 {
+		t.Fatalf("localhost A: %+v, %v", got, err)
+	}
+	if _, err := CheckDNS("localhost", "SRV", time.Second); err == nil {
+		t.Fatal("an unknown record type was accepted")
+	}
+	got, err = CheckDNS("no-such-name.invalid", "A", time.Second)
+	if err != nil || got.Error == "" || len(got.Answers) != 0 {
+		t.Fatalf("a name that does not resolve is a result with its error: %+v, %v", got, err)
+	}
+}
+
+func TestTimeoutIsDefaultedAndBounded(t *testing.T) {
+	if d, _ := timeoutOf(map[string]any{}); d != DefaultTimeout {
+		t.Errorf("default: %v", d)
+	}
+	if d, _ := timeoutOf(map[string]any{"timeout_ms": float64(10 * 60 * 1000)}); d != MostTimeout {
+		t.Errorf("bounded: %v", d)
+	}
+	if _, err := timeoutOf(map[string]any{"timeout_ms": float64(0)}); err == nil {
+		t.Error("a zero timeout was accepted")
+	}
+}
+
+func TestBothToolsAreListedUnprefixed(t *testing.T) {
+	names := map[string]bool{}
+	for _, tool := range tools() {
+		names[tool.Name] = true
+	}
+	if !names["netcheck_tcp"] || !names["netcheck_dns"] || len(names) != 2 {
+		t.Fatalf("tools: %v", names)
+	}
+}
diff --git a/modules/netcheck/cmd/netcheck/main.go b/modules/netcheck/cmd/netcheck/main.go
new file mode 100644
index 0000000..98cb507
--- /dev/null
+++ b/modules/netcheck/cmd/netcheck/main.go
@@ -0,0 +1,72 @@
+// netcheck's Go tools bundle (novox/hq ADR 0188, ADR 0193): a process the node's runtime launches
+// and speaks MCP over stdio to, through the Go SDK. It serves the two checks that are the machine's
+// own sockets and resolver — a TCP connect and a DNS lookup — and nothing that changes anything.
+// The module's HTTP check is its TypeScript bundle; the runtime serves both under one module.
+package main
+
+import (
+	"fmt"
+	"os"
+
+	stdio "git.novox.be/novox/mesh-sdk/go"
+)
+
+func main() {
+	// An empty name serves as the module the runtime names (MESH_SERVED_MODULE): netcheck.
+	if err := stdio.Serve("", tools()); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+func tools() []stdio.Tool {
+	return []stdio.Tool{
+		{
+			Name: "netcheck_tcp",
+			Description: "Check whether a TCP port is reachable from this machine: opens one connection " +
+				"and closes it at once, sending nothing. Answers reachable, elapsed_ms and the error when not.",
+			Input: map[string]any{
+				"host":       map[string]any{"type": "string", "description": "host name or IP address"},
+				"port":       map[string]any{"type": "integer", "description": "TCP port, 1-65535"},
+				"timeout_ms": map[string]any{"type": "integer", "description": "give up after this long (default 3000, at most 30000)"},
+			},
+			Run: func(args map[string]any) (any, error) {
+				host, err := text(args, "host")
+				if err != nil {
+					return nil, err
+				}
+				port, err := whole(args, "port", 0)
+				if err != nil {
+					return nil, err
+				}
+				timeout, err := timeoutOf(args)
+				if err != nil {
+					return nil, err
+				}
+				return CheckTCP(host, port, timeout)
+			},
+		},
+		{
+			Name: "netcheck_dns",
+			Description: "Look a name up with this machine's resolver (its /etc/resolv.conf and /etc/hosts). " +
+				"type is A, AAAA, CNAME, TXT or MX; answers the records found, or the error.",
+			Input: map[string]any{
+				"name":       map[string]any{"type": "string", "description": "the name to look up"},
+				"type":       map[string]any{"type": "string", "enum": []string{"A", "AAAA", "CNAME", "TXT", "MX"}, "description": "record type (default A)"},
+				"timeout_ms": map[string]any{"type": "integer", "description": "give up after this long (default 3000, at most 30000)"},
+			},
+			Run: func(args map[string]any) (any, error) {
+				name, err := text(args, "name")
+				if err != nil {
+					return nil, err
+				}
+				kind, _ := args["type"].(string)
+				timeout, err := timeoutOf(args)
+				if err != nil {
+					return nil, err
+				}
+				return CheckDNS(name, kind, timeout)
+			},
+		},
+	}
+}
diff --git a/modules/netcheck/go.mod b/modules/netcheck/go.mod
new file mode 100644
index 0000000..83fdfe3
--- /dev/null
+++ b/modules/netcheck/go.mod
@@ -0,0 +1,5 @@
+module netcheck
+
+go 1.22
+
+require git.novox.be/novox/mesh-sdk/go v0.1.6
diff --git a/modules/netcheck/go.sum b/modules/netcheck/go.sum
new file mode 100644
index 0000000..0dd6061
--- /dev/null
+++ b/modules/netcheck/go.sum
@@ -0,0 +1,2 @@
+git.novox.be/novox/mesh-sdk/go v0.1.6 h1:9qzdYONYbJdWcu6sxQcq9v1LI0JxcfkiKYkMUzJSkVQ=
+git.novox.be/novox/mesh-sdk/go v0.1.6/go.mod h1:GFuZUElBZ9A++mxgIKo97aXXo+kV0uJ/UkbhQPPIbrY=
diff --git a/modules/netcheck/http.ts b/modules/netcheck/http.ts
new file mode 100644
index 0000000..0a49add
--- /dev/null
+++ b/modules/netcheck/http.ts
@@ -0,0 +1,84 @@
+// netcheck's HTTP check — the module's own code, in TypeScript (novox/hq ADR 0039, ADR 0188). One
+// request, HEAD or GET, never a body sent and never a body read: the status, how long it took and
+// a few headers that say what answered. Redirects are reported, not followed, so a check reaches
+// exactly the address it was given.
+
+export const METHODS = ["HEAD", "GET"] as const;
+export type Method = (typeof METHODS)[number];
+
+/** The headers worth reporting: what answered and what it says it is, nothing it set for a client. */
+export const REPORTED_HEADERS = [
+  "content-type", "content-length", "server", "location", "date",
+  "cache-control", "last-modified", "etag",
+] as const;
+
+export const DEFAULT_TIMEOUT_MS = 5000;
+export const MOST_TIMEOUT_MS = 30000;
+
+export interface HttpResult {
+  url: string;
+  method: Method;
+  status?: number;
+  statusText?: string;
+  elapsed_ms: number;
+  headers: Record<string, string>;
+  error?: string;
+}
+
+/** Only http and https are checked; anything else — file:, data:, ftp: — is refused by name. */
+export function checkedUrl(raw: unknown): URL {
+  const text = typeof raw === "string" ? raw.trim() : "";
+  if (!text) throw new Error("url is required");
+  let url: URL;
+  try {
+    url = new URL(text);
+  } catch {
+    throw new Error(`${JSON.stringify(text)} is not a URL`);
+  }
+  if (url.protocol !== "http:" && url.protocol !== "https:") {
+    throw new Error(`netcheck_http checks http and https URLs only, not ${url.protocol}`);
+  }
+  return url;
+}
+
+export function checkedMethod(raw: unknown): Method {
+  const m = (typeof raw === "string" && raw.trim() ? raw.trim() : "HEAD").toUpperCase();
+  if (!(METHODS as readonly string[]).includes(m)) {
+    throw new Error(`method ${m} is not one netcheck_http uses (${METHODS.join(", ")}): a check never changes anything`);
+  }
+  return m as Method;
+}
+
+export function checkedTimeout(raw: unknown): number {
+  if (raw === undefined || raw === null || raw === "") return DEFAULT_TIMEOUT_MS;
+  const n = Number(raw);
+  if (!Number.isInteger(n) || n < 1) throw new Error(`timeout_ms must be a whole number of at least 1, not ${String(raw)}`);
+  return Math.min(n, MOST_TIMEOUT_MS);
+}
+
+/** Make one request and report how it went. A refused connection or a timeout is a result with its
+ *  error; only a malformed question throws. */
+export async function checkHttp(args: Readonly<Record<string, unknown>>, fetcher: typeof fetch = fetch): Promise<HttpResult> {
+  const url = checkedUrl(args.url);
+  const method = checkedMethod(args.method);
+  const timeout = checkedTimeout(args.timeout_ms);
+  const started = performance.now();
+  const out: HttpResult = { url: url.toString(), method, elapsed_ms: 0, headers: {} };
+  try {
+    const res = await fetcher(url, { method, redirect: "manual", signal: AbortSignal.timeout(timeout) });
+    out.elapsed_ms = Math.round(performance.now() - started);
+    out.status = res.status;
+    out.statusText = res.statusText;
+    for (const h of REPORTED_HEADERS) {
+      const v = res.headers.get(h);
+      if (v !== null) out.headers[h] = v;
+    }
+    // The body is not read: a check asks whether something answers, not what it says.
+    await res.body?.cancel().catch(() => {});
+  } catch (err) {
+    out.elapsed_ms = Math.round(performance.now() - started);
+    const e = err as Error & { cause?: { message?: string; code?: string } };
+    out.error = e.name === "TimeoutError" ? `no answer within ${timeout} ms` : (e.cause?.code ?? e.cause?.message ?? e.message);
+  }
+  return out;
+}
diff --git a/modules/netcheck/module.json b/modules/netcheck/module.json
new file mode 100644
index 0000000..9ee8e8f
--- /dev/null
+++ b/modules/netcheck/module.json
@@ -0,0 +1,35 @@
+{
+  "module": "netcheck",
+  "version": "1",
+  "tools": [
+    "netcheck_tcp",
+    "netcheck_dns",
+    "netcheck_http"
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "tools-go",
+        "kind": "bundle",
+        "language": "go",
+        "system": "arch",
+        "from": "cmd/netcheck",
+        "binary": "netcheck",
+        "loads": [
+          "netcheck"
+        ]
+      },
+      {
+        "name": "tools-typescript",
+        "kind": "bundle",
+        "language": "typescript",
+        "entrypoints": [
+          "tools/index.js"
+        ],
+        "loads": [
+          "tools/index.js"
+        ]
+      }
+    ]
+  }
+}
diff --git a/modules/netcheck/package.json b/modules/netcheck/package.json
new file mode 100644
index 0000000..5d96e26
--- /dev/null
+++ b/modules/netcheck/package.json
@@ -0,0 +1,17 @@
+{
+  "name": "@novox/module-netcheck",
+  "version": "0.1.0",
+  "description": "netcheck — read-only network checks from a machine, as one module carrying a Go tools bundle (TCP, DNS) and a TypeScript one (HTTP) (novox/hq ADR 0188, ADR 0193).",
+  "type": "module",
+  "private": true,
+  "scripts": {
+    "test": "node --test --experimental-strip-types 'test/*.test.ts'"
+  },
+  "dependencies": {
+    "@novox/mesh-sdk": "^0.1.6"
+  },
+  "devDependencies": {
+    "@types/node": "^22.0.0",
+    "typescript": "^5.6.0"
+  }
+}
diff --git a/modules/netcheck/test/http.test.ts b/modules/netcheck/test/http.test.ts
new file mode 100644
index 0000000..bec2566
--- /dev/null
+++ b/modules/netcheck/test/http.test.ts
@@ -0,0 +1,52 @@
+// The HTTP check refuses what is not http(s) and what would change something, and reports a status,
+// a refusal and a timeout as results (novox/hq ADR 0188: a tools bundle is read-only and harmless).
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { createServer } from "node:http";
+import type { AddressInfo } from "node:net";
+import { checkHttp, checkedMethod, checkedUrl } from "../http.ts";
+
+test("only http and https URLs are checked", () => {
+  for (const bad of ["file:///etc/passwd", "ftp://example.org/", "data:text/plain,hi", "javascript:1", "", "not a url"]) {
+    assert.throws(() => checkedUrl(bad), `${bad} was accepted`);
+  }
+  assert.equal(checkedUrl("https://example.org/x").protocol, "https:");
+});
+
+test("only HEAD and GET are used", () => {
+  assert.equal(checkedMethod(undefined), "HEAD");
+  assert.equal(checkedMethod("get"), "GET");
+  for (const bad of ["POST", "PUT", "DELETE", "PATCH"]) assert.throws(() => checkedMethod(bad));
+});
+
+test("a status, its headers and a redirect not followed", async () => {
+  const server = createServer((req, res) => {
+    if (req.url === "/moved") { res.writeHead(302, { location: "/elsewhere" }); res.end(); return; }
+    res.writeHead(200, { "content-type": "text/plain", "x-secret": "not reported" });
+    res.end(req.method === "GET" ? "body" : undefined);
+  });
+  await new Promise<void>((ok) => server.listen(0, "127.0.0.1", ok));
+  const base = `http://127.0.0.1:${(server.address() as AddressInfo).port}`;
+  try {
+    const head = await checkHttp({ url: base + "/" });
+    assert.equal(head.status, 200);
+    assert.equal(head.method, "HEAD");
+    assert.equal(head.headers["content-type"], "text/plain");
+    assert.equal(head.headers["x-secret"], undefined);
+    const moved = await checkHttp({ url: base + "/moved", method: "GET" });
+    assert.equal(moved.status, 302);
+    assert.equal(moved.headers.location, "/elsewhere");
+  } finally {
+    server.close();
+  }
+});
+
+test("a refused connection is a result with its error", async () => {
+  const server = createServer();
+  await new Promise<void>((ok) => server.listen(0, "127.0.0.1", ok));
+  const port = (server.address() as AddressInfo).port;
+  await new Promise<void>((ok) => server.close(() => ok()));
+  const got = await checkHttp({ url: `http://127.0.0.1:${port}/`, timeout_ms: 2000 });
+  assert.equal(got.status, undefined);
+  assert.ok(got.error, "no error reported");
+});
diff --git a/modules/netcheck/tools/index.ts b/modules/netcheck/tools/index.ts
new file mode 100644
index 0000000..701089a
--- /dev/null
+++ b/modules/netcheck/tools/index.ts
@@ -0,0 +1,28 @@
+// netcheck's TypeScript tools bundle (novox/hq ADR 0188, ADR 0193): what the builder's launcher
+// imports and serves over MCP on stdio. Its Go bundle serves the TCP and DNS checks; this one the
+// HTTP check — one module, two languages, one runtime that knows neither.
+
+import { registerModuleTools, type ToolDefinition } from "@novox/mesh-sdk/tools";
+import { checkHttp, DEFAULT_TIMEOUT_MS, METHODS, MOST_TIMEOUT_MS } from "../http.js";
+
+export function getNetcheckHttpTools(): ToolDefinition[] {
+  return [
+    {
+      name: "netcheck_http",
+      description:
+        "Check whether an http(s) URL answers from this machine: one HEAD or GET, no body sent or read, " +
+        "redirects reported and not followed. Answers status, elapsed_ms and a few headers.",
+      input: {
+        url: { type: "string", description: "an http:// or https:// URL" },
+        method: { type: "string", enum: [...METHODS], description: "HEAD (default) or GET" },
+        timeout_ms: {
+          type: "integer",
+          description: `give up after this long (default ${DEFAULT_TIMEOUT_MS}, at most ${MOST_TIMEOUT_MS})`,
+        },
+      },
+      run: async (args) => checkHttp(args),
+    },
+  ];
+}
+
+registerModuleTools("netcheck", () => getNetcheckHttpTools());
diff --git a/modules/netcheck/tsconfig.json b/modules/netcheck/tsconfig.json
new file mode 100644
index 0000000..e4f66ed
--- /dev/null
+++ b/modules/netcheck/tsconfig.json
@@ -0,0 +1,12 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "noEmit": true
+  },
+  "include": ["http.ts", "tools/index.ts"]
+}