/Wiki/sources/honojs__hono/2026/https-hono-dev-llms-full-txt-manual-validator-78b974053630-manual-validator-s0101-c0004.md
Manual validator (5) - hono-docs
Manual validator (5) Source evidence: /Sources/raw/honojs hono/honojs hono.md Canonical citation: https://hono.dev/llms full.txt manual validator Summary ts...
Manual validator (5)
Source evidence: /Sources/raw/honojshono/honojshono.md Canonical citation: https://hono.dev/llms-full.txt#manual-validator
Summary
## Content
```ts
// ❌ this will not work
app.post(
'/api',
validator('header', (value, c) => {
// idempotencyKey is always undefined
// so this middleware always return 400 as not expected
const idempotencyKey = value['Idempotency-Key']
if (idempotencyKey == undefined || idempotencyKey === '') {
throw new HTTPException(400, {
message: 'Idempotency-Key is required',
})
}
return { idempotencyKey }
}),
(c) => {
const { idempotencyKey } = c.req.valid('header')
// ...
}
)
// ✅ this will work
app.post(
'/api',
validator('header', (value, c) => {
// can retrieve the value of the header as expected
const idempotencyKey = value['idempotency-key']
if (idempotencyKey == undefined || idempotencyKey === '') {
throw new HTTPException(400, {
message: 'Idempotency-Key is required',
})
}
return { idempotencyKey }
}),
(c) => {
const { idempotencyKey } = c.req.valid('header')
// ...
}
)
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