diff --git a/ismism.ts/src/eid/is.ts b/ismism.ts/src/eid/is.ts
new file mode 100644
index 0000000..14daaed
--- /dev/null
+++ b/ismism.ts/src/eid/is.ts
@@ -0,0 +1,142 @@
+import type { Act, Agd, Aut, Id, Itm, Mnu, Ord, Rec } from "./typ.ts"
+
+export const lim_nam = 16
+export const lim_intro = 2048
+export const lim_msg = 256
+export const lim_src = 256
+export const lim_jwt = 512
+export const len_code = 6
+export const lim_code = 10 ** len_code
+
+export const lst_re = 2
+export const lim_re = 64
+
+export const lim_sec = 8
+export const lim_uid = 128
+export const lim_res = 64
+
+export const lim_itm = 16
+export const lim_loc = 16
+
+export const lim_gol = 8
+export const lim_img = 8
+export const lim_mnu = 2
+
+export const lim_mrk = 5
+export const lim_dst = 24
+
+export const lim_md = 2048 * 8
+export const lim_pin = 4
+
+export const lim_sup = 1
+export const lim_aud = 1
+export const lim_aut = 7
+
+export function is_lim(
+	n: number,
+	lim: number,
+) {
+	return 0 <= n && n <= lim
+}
+
+export function is_id(
+	id: Id["_id"]
+) {
+	return typeof id === "number" && id > 0
+}
+export function is_idl(
+	id: Id["_id"][],
+	lim: number,
+) {
+	return id.length <= lim && id.every(is_id)
+}
+export function is_nam(
+	nam: string
+) {
+	return typeof nam === "string" && /^[\u4E00-\u9FFF]{2,16}$/.test(nam)
+}
+export function is_intro(
+	intro: Id["intro"]
+) {
+	return typeof intro === "string" && intro.length <= lim_intro
+}
+export function is_msg(
+	msg: string
+) {
+	return typeof msg === "string" && 2 <= msg.length && msg.length <= lim_msg
+}
+export function is_src(
+	src: string
+) {
+	return typeof src === "string" && src.length <= lim_src && src.startsWith("http")
+}
+
+export function is_itm(
+	itm: Itm
+) {
+	return Object.keys(itm).length === 3 && is_nam(itm.nam) && itm.rmb >= 0 && itm.amt >= 0
+}
+export function is_loc(
+	loc: Mnu["loc"][0]
+) {
+	Object.keys(loc).length === 2 && is_nam(loc.nam) && is_src(loc.src)
+}
+export function is_mnu(
+	mnu: Mnu
+) {
+	return Object.keys(mnu).length === 5
+		&& is_nam(mnu.nam)
+		&& Object.keys(mnu.utc).length === 2 && mnu.utc.end >= mnu.utc.start
+		&& Object.keys(mnu.lim).length === 3 && mnu.lim.amt >= 0 && mnu.lim.sum >= 0 && mnu.lim.week >= 0
+		&& mnu.itm.every(is_itm) && mnu.loc.every(is_loc)
+}
+export function is_acc(
+	acc: Agd["acc"]
+) {
+	return Object.keys(acc).length === 4 && is_src(acc.src)
+		&& acc.expense <= acc.fund && acc.fund <= acc.budget
+}
+export function is_gol(
+	gol: Agd["gol"]
+) {
+	return gol.length <= lim_gol && gol.every(g =>
+		Object.keys(g).length === 2 && is_nam(g.nam) && is_lim(g.pct, 100)
+	)
+}
+export function is_img(
+	img: Agd["img"]
+) {
+	return img.length <= lim_img && img.every(m =>
+		Object.keys(m).length === 2 && is_nam(m.nam) && is_src(m.src)
+	)
+}
+
+export function is_recid(
+	recid: Rec["_id"]
+) {
+	return Object.keys(recid).length === 3 && is_id(recid.uid) && is_id(recid.aid) && Number.isInteger(recid.utc)
+}
+export function is_rev(
+	rev: NonNullable<Ord["rev"]>
+) {
+	return Object.keys(rev).length === 3 && is_idl(rev.uid, lim_re) && is_lim(rev.mrk, lim_mrk) && is_msg(rev.msg)
+}
+
+export function is_md(
+	md: string
+) {
+	return typeof md === "string" && md.length <= lim_md
+}
+
+export function is_aut(
+	aut: Aut["aut"],
+	a?: Aut["aut"][0],
+) {
+	return aut.every(a => ["sup", "aud", "aut", "wsl", "lit"].includes(a))
+		&& (!a || aut.includes(a))
+}
+export function is_actid(
+	actid: Act["_id"]
+) {
+	return typeof actid === "string" && len_code <= actid.length && actid.length <= lim_jwt
+}