# HINTS stroke in acute vestibular syndrome

HINTS

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/hints`
HTML: https://magentlab.com/docs/hints
Markdown: https://magentlab.com/docs/hints.md

Not a medical device. Not a diagnosis, dose, or listing recommendation.

## What it computes

Apply the Kattah 2009 three-step HINTS exam (Head-Impulse, Nystagmus, Test-of-Skew) from three caller-assigned flags and return whether any dangerous central sign is present.

## When to use

When an agent already has the three HINTS flags for a patient already in acute vestibular syndrome (AVS) as in Kattah 2009 and needs whether the published three-step exam is dangerous or benign. magent does not examine the patient.

## When not to use

- Not a medical device.
- Not a stroke diagnosis. magent does not examine the patient.
- For patients already in acute vestibular syndrome (AVS) as in Kattah 2009. The caller assigns the three HINTS flags.
- This is three-step HINTS only. Not HINTS-plus (hearing). magent does not take hearing loss, eye/verbal/motor GCS, or mortality tables.
- Not a substitute for neuroimaging.

## Formula

```
dangerous iff head_impulse_normal or direction_changing_nystagmus or skew_deviation; benign iff not dangerous (Kattah 2009 three-step HINTS for acute vestibular syndrome; INFARCT: Impulse Normal, Fast-phase Alternating, Refixation on Cover Test)
```

## Citation

[HINTS to Diagnose Stroke in the Acute Vestibular Syndrome](https://doi.org/10.1161/STROKEAHA.109.551234)
Kattah JC, Talkad AV, Wang DZ, Hsieh YH, Newman-Toker DE
Stroke. 2009;40(11):3504-3510
DOI: [10.1161/STROKEAHA.109.551234](https://doi.org/10.1161/STROKEAHA.109.551234)

## Worked example

### All three flags false (benign peripheral pattern)

Given: `direction_changing_nystagmus=false, head_impulse_normal=false, skew_deviation=false`

1. head_impulse_normal false (abnormal HIT implied)
2. direction_changing_nystagmus false
3. skew_deviation false
4. dangerous_any is false; dangerous is false; benign is true


### Normal head-impulse only (dangerous central sign)

Given: `direction_changing_nystagmus=false, head_impulse_normal=true, skew_deviation=false`

1. head_impulse_normal true is a dangerous central sign (INFARCT: Impulse Normal)
2. The other two flags are false
3. dangerous_any is true; dangerous is true; benign is false


## Also searched as

- HINTS exam
- HINTS stroke
- Head Impulse Nystagmus Test of Skew
- Kattah 2009 HINTS
- acute vestibular syndrome HINTS
- INFARCT HINTS
- HINTS AVS
- central vs peripheral vertigo

## Parameters

- `head_impulse_normal` (boolean, required): Normal horizontal head-impulse test (h-HIT) as assigned by the caller (Kattah 2009). true is a dangerous central sign (INFARCT: Impulse Normal). magent does not examine the patient.
- `direction_changing_nystagmus` (boolean, required): Direction-changing nystagmus in eccentric gaze as assigned by the caller (Kattah 2009). true is a dangerous central sign (INFARCT: Fast-phase Alternating). magent does not examine the patient.
- `skew_deviation` (boolean, required): Skew deviation / vertical ocular misalignment on cover test as assigned by the caller (Kattah 2009). true is a dangerous central sign (INFARCT: Refixation on Cover Test). magent does not examine the patient.

## Bulk (POST)

POST the same path with a JSON items array. The first item is the GET unit; each additional item is $0.002. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/hints`
Max items: 25
Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- POST of 1 item costs the same as GET. Lists longer than 25: chunk into multiple POSTs. Extra items still execute; do not pad dummy rows.
- The first invalid item fails the whole request (index in the 400 JSON). You are not charged.
- HTTP 200 is {count, path, items}. Each items[i] is the GET 200 body for that row.
- Catalog misses (empty matches, found=false) stay paid 200s inside that slot.
- x402 resource URL is this path plus n and body_sha256. Browsers that prefer text/html get the same paywall as GET; Pay retries POST with the same items.

Example request:

```json
{
  "items": [
    {
      "direction_changing_nystagmus": "false",
      "head_impulse_normal": "false",
      "skew_deviation": "false"
    },
    {
      "direction_changing_nystagmus": "false",
      "head_impulse_normal": "false",
      "skew_deviation": "false"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/hints

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/hints",
  "items": [
    {
      "benign": true,
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Kattah JC, Talkad AV, Wang DZ, Hsieh YH, Newman-Toker DE",
        "doi": "10.1161/STROKEAHA.109.551234",
        "id": "kattah-2009",
        "pmid": "19762709",
        "source": "Stroke. 2009;40(11):3504-3510",
        "title": "HINTS to Diagnose Stroke in the Acute Vestibular Syndrome"
      },
      "formula": "hints",
      "formula_expression": "dangerous iff head_impulse_normal or direction_changing_nystagmus or skew_deviation; benign iff not dangerous (Kattah 2009 three-step HINTS for acute vestibular syndrome; INFARCT: Impulse Normal, Fast-phase Alternating, Refixation on Cover Test)",
      "criteria": [
        {
          "factor": "head_impulse_normal",
          "met": false
        },
        {
          "factor": "direction_changing_nystagmus",
          "met": false
        },
        {
          "factor": "skew_deviation",
          "met": false
        },
        {
          "factor": "dangerous_any",
          "met": false
        }
      ],
      "dangerous": false
    },
    {
      "benign": true,
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Kattah JC, Talkad AV, Wang DZ, Hsieh YH, Newman-Toker DE",
        "doi": "10.1161/STROKEAHA.109.551234",
        "id": "kattah-2009",
        "pmid": "19762709",
        "source": "Stroke. 2009;40(11):3504-3510",
        "title": "HINTS to Diagnose Stroke in the Acute Vestibular Syndrome"
      },
      "formula": "hints",
      "formula_expression": "dangerous iff head_impulse_normal or direction_changing_nystagmus or skew_deviation; benign iff not dangerous (Kattah 2009 three-step HINTS for acute vestibular syndrome; INFARCT: Impulse Normal, Fast-phase Alternating, Refixation on Cover Test)",
      "criteria": [
        {
          "factor": "head_impulse_normal",
          "met": false
        },
        {
          "factor": "direction_changing_nystagmus",
          "met": false
        },
        {
          "factor": "skew_deviation",
          "met": false
        },
        {
          "factor": "dangerous_any",
          "met": false
        }
      ],
      "dangerous": false
    }
  ]
}
```

## Response fields

- `formula` (string): hints
- `formula_expression` (string): Kattah 2009 three-step HINTS: dangerous if any of the three caller-assigned central signs
- `dangerous` (boolean): true iff any of head_impulse_normal, direction_changing_nystagmus, or skew_deviation is true (INFARCT). Not a stroke diagnosis.
- `benign` (boolean): true iff none of the three central signs is true (not dangerous)
- `criteria` (array): Per-flag rows plus dangerous_any (met iff any of the three flags is true)
- `citation` (object): Kattah 2009 Stroke citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "benign": true,
  "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
  "citation": {
    "authors": "Kattah JC, Talkad AV, Wang DZ, Hsieh YH, Newman-Toker DE",
    "doi": "10.1161/STROKEAHA.109.551234",
    "id": "kattah-2009",
    "pmid": "19762709",
    "source": "Stroke. 2009;40(11):3504-3510",
    "title": "HINTS to Diagnose Stroke in the Acute Vestibular Syndrome"
  },
  "formula": "hints",
  "formula_expression": "dangerous iff head_impulse_normal or direction_changing_nystagmus or skew_deviation; benign iff not dangerous (Kattah 2009 three-step HINTS for acute vestibular syndrome; INFARCT: Impulse Normal, Fast-phase Alternating, Refixation on Cover Test)",
  "criteria": [
    {
      "factor": "head_impulse_normal",
      "met": false
    },
    {
      "factor": "direction_changing_nystagmus",
      "met": false
    },
    {
      "factor": "skew_deviation",
      "met": false
    },
    {
      "factor": "dangerous_any",
      "met": false
    }
  ],
  "dangerous": false
}
```

## Errors

- HTTP 400 `invalid_flag`: boolean clinical flags must be true or false Returned before settlement; you are not charged.
- HTTP 400 `invalid_items`: POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
- HTTP 400 `invalid_item_count`: items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
- HTTP 400 `invalid_item`: each items entry must be a JSON object Returned before settlement; you are not charged.

Shared HTTP 402 and 503: https://magentlab.com/docs/payments

## Related tools

- [Glasgow Coma Scale](https://magentlab.com/docs/gcs) — Compute the Glasgow Coma Scale as the sum of caller-assigned eye, verbal, and motor integers. The 1974 or 1976 edition is required.
- [GCS-Pupils](https://magentlab.com/docs/gcs-pupils) — Return the Brennan 2018 GCS-Pupils index as caller-assigned total GCS 3-15 minus pupil reactivity score (unreactive pupils 0, 1, or 2).
- [ROSIER](https://magentlab.com/docs/rosier) — Sum the seven Nor 2005 ROSIER items from caller-assigned flags and return whether the score is greater than 0 (stroke more likely).

## Payment

Unpaid requests return HTTP 402 even if query parameters or POST items are missing or invalid, so CDP and agents can index the path. After a PAYMENT-SIGNATURE, invalid params return HTTP 400 JSON before settlement. magent does not charge. Fix the params, then request a new 402 quote for that complete URL. Catalog misses (empty matches, found=false) are valid paid 200s.

- GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall).
- HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote.
- Sign accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON of accepted and payload). Magent attaches canonical extensions.bazaar on CDP verify/settle; echoing 402 bazaar is optional.
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact nonce only after a new HTTP 402.

- offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront.
- offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization.

- not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search.

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers).

Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments

Stdio MCP (one process per host): https://magentlab.com/docs/mcp

## Guarantees

- HTTP 402 is unpaid, including a missing query. After PAYMENT-SIGNATURE, invalid parameters return HTTP 400 before settlement. You are not charged. HTTP 402 never includes the tool JSON.
- exact: settlement finishes before the tool (paymentFlow upfront). batch-settlement: verify/deposit before the tool; chargedCumulativeAmount commits after HTTP 2xx. Uncertain or failed settlement fails closed (HTTP 503). Retry the same PAYMENT-SIGNATURE.
- HTTP 402 is unpaid only. Do not sign a second authorization because of a 503.
- Execution is timeout-bounded and concurrency-capped.
- Calculator inputs are stored encrypted for allowlisted operators (Magent Console). They are not in public logs, SSH lookups, catalog, or rollups. Request logs store path without query.