# SAVE-score (Schmidt 2015)

SAVE-score

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

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

## What it computes

Sum Schmidt 2015 Table 4 SAVE-score cells including the published constant −6 and return class I–V with hospital survival percents.

## When to use

When an agent has caller-assigned pre-ECMO Table 4 predictors and needs the published integer SAVE-score and class, not a cannulation order and not Chen 2016 modified SAVE.

## When not to use

- Not a medical device. magent does not assign VA-ECMO, does not cannulate, and does not examine the patient.
- Not a cannulation order, eCPR protocol, or futility determination. Derivation excluded ECMO during CPR.
- Schmidt 2015 Table 4 only, plus the published constant −6. Not Chen 2016 modified SAVE (no lactate cell). Not RESP (VV-ECMO).
- Diagnoses and acute pre-ECMO organ failures may stack (Table 4: select one or more). Other diagnoses score 0. Acute and chronic renal failure are separate cells.
- A score of 0 is approximately 50% hospital survival in the paper text; this tool returns the Table 4 class percent (I 75, II 58, III 42, IV 30, V 18), not a continuous logit.
- Organ-failure flags, PIP, blood pressure, pulse pressure, and bicarbonate are caller-assigned. magent does not measure labs or airway pressure.

## Formula

```
SAVE = constant(−6) + age(18–38 → 7, 39–52 → 4, 53–62 → 3, ≥63 → 0) + weight_kg(≤65 → 1, 66–89 → 2, ≥90 → 0) + myocarditis(3) + refractory_vt_vf(2) + post_heart_or_lung_transplant(3) + congenital_heart_disease(−3) + liver_failure(−3) + cns_dysfunction(−3) + acute_renal_failure(−3) + chronic_renal_failure(−6) + intubation_hours(≤10 → 0, 11–29 → −2, ≥30 → −4) + pip_cmh2o(≤20 → 3) + pre_ecmo_cardiac_arrest(−2) + diastolic_bp_mm_hg(≥40 → 3) + pulse_pressure_mm_hg(≤20 → −2) + bicarbonate_mmol_l(≤15 → −3); diagnoses and acute organ failures may stack (Table 4 select one or more); other diagnoses 0; range −35 to 17; class I >5 → 75%, II 1–5 → 58%, III −4 to 0 → 42%, IV −9 to −5 → 30%, V ≤−10 → 18%
```

## Citation

[Predicting survival after ECMO for refractory cardiogenic shock: the survival after veno-arterial-ECMO (SAVE)-score](https://doi.org/10.1093/eurheartj/ehv194)
Schmidt M, Burrell A, Roberts L, et al.
Eur Heart J. 2015;36(33):2246-2256
DOI: [10.1093/eurheartj/ehv194](https://doi.org/10.1093/eurheartj/ehv194)

## Worked example

### Offset-only adult row (constant −6, no other Table 4 cells)

Given: `acute_renal_failure=false, age=70, bicarbonate_mmol_l=24, chronic_renal_failure=false, cns_dysfunction=false, congenital_heart_disease=false, diastolic_bp_mm_hg=35, intubation_hours=5, liver_failure=false, myocarditis=false, pip_cmh2o=25, post_heart_or_lung_transplant=false, pre_ecmo_cardiac_arrest=false, pulse_pressure_mm_hg=40, refractory_vt_vf=false, weight_kg=95`

1. Age ≥63 → 0; weight ≥90 → 0; no diagnosis flags → 0; no organ-failure flags → 0
2. Intubation ≤10 → 0; PIP >20 → 0; no arrest → 0; DBP <40 → 0; pulse pressure >20 → 0; HCO3 >15 → 0
3. Constant −6 on every row
4. Score = −6; class IV (−9 to −5); hospital_survival_percent 30


### Younger age, myocarditis, and other Table 4 protective cells

Given: `acute_renal_failure=false, age=30, bicarbonate_mmol_l=24, chronic_renal_failure=false, cns_dysfunction=false, congenital_heart_disease=false, diastolic_bp_mm_hg=45, intubation_hours=5, liver_failure=false, myocarditis=true, pip_cmh2o=18, post_heart_or_lung_transplant=false, pre_ecmo_cardiac_arrest=false, pulse_pressure_mm_hg=40, refractory_vt_vf=false, weight_kg=70`

1. Age 18–38 → 7; weight 66–89 → 2; myocarditis → 3; PIP ≤20 → 3; DBP ≥40 → 3
2. No stacked forbidden cells; congenital false; no risk cells
3. Constant −6
4. Score = 7+2+3+3+3−6 = 12; class I; hospital_survival_percent 75


## Also searched as

- SAVE score
- SAVE-score
- survival after VA-ECMO
- Schmidt SAVE
- veno-arterial ECMO survival
- hospital survival after ECMO
- VA-ECMO SAVE

## Parameters

- `age` (integer, required): Age in years (18-120). Schmidt 2015 Table 4: 18–38 → 7, 39–52 → 4, 53–62 → 3, ≥63 → 0. Adult SAVE-score; magent does not assign pediatric VA-ECMO.
- `weight_kg` (number, required): Weight in kg (20-400). Table 4 / Table 3 bands: ≤65 → 1, 66–89 → 2, ≥90 → 0. 65 kg scores 1 (≤65 before the 65–89 typeset overlap). Caller-supplied; magent does not weigh the patient.
- `myocarditis` (boolean, required): Acute myocarditis diagnosis (Table 4, +3). Diagnoses are not mutually exclusive (select one or more). true or false. Caller-assigned.
- `refractory_vt_vf` (boolean, required): Refractory ventricular tachycardia or fibrillation (Table 4, +2). May stack with other diagnosis flags. true or false. Caller-assigned.
- `post_heart_or_lung_transplant` (boolean, required): Post heart or lung transplantation (Table 4, +3). May stack with other diagnosis flags. true or false. Caller-assigned.
- `congenital_heart_disease` (boolean, required): Congenital heart disease (Table 4, −3). May stack with other diagnosis flags. true or false. Caller-assigned.
- `liver_failure` (boolean, required): Acute pre-ECMO liver failure (Table 4, −3). Paper footnote: bilirubin ≥33 µmol/L or ALT or AST >70 U/L. Acute organ failures may stack. true or false. Caller-assigned; magent does not measure labs.
- `cns_dysfunction` (boolean, required): Acute pre-ECMO CNS dysfunction (Table 4, −3): neurotrauma, stroke, encephalopathy, cerebral embolism, seizure or epileptic syndromes. May stack. true or false. Caller-assigned; magent does not examine the patient.
- `acute_renal_failure` (boolean, required): Acute pre-ECMO renal failure (Table 4, −3): creatinine >1.5 mg/dL with or without RRT. Distinct from chronic_renal_failure. May stack. true or false. Caller-assigned.
- `chronic_renal_failure` (boolean, required): Chronic renal failure (Table 4, −6): kidney damage or GFR <60 mL/min/1.73 m² for ≥3 months. Distinct from acute_renal_failure. true or false. Caller-assigned.
- `intubation_hours` (number, required): Hours of intubation before ECMO (0-720). Table 4: ≤10 → 0, 11–29 → −2, ≥30 → −4. Caller-supplied; magent does not read a ventilator log.
- `pip_cmh2o` (number, required): Peak inspiratory pressure in cmH2O (5-80). Table 4: ≤20 → +3, otherwise 0. Worst value as assigned by the caller. magent does not read airway pressure.
- `pre_ecmo_cardiac_arrest` (boolean, required): Cardiac arrest before ECMO (Table 4, −2). Derivation excluded eCPR during cannulation. true or false. Caller-assigned.
- `diastolic_bp_mm_hg` (number, required): Diastolic blood pressure in mm Hg before ECMO (1-200). Worst value within 6 h of cannulation. Table 4: ≥40 → +3, otherwise 0. magent does not measure blood pressure.
- `pulse_pressure_mm_hg` (number, required): Pulse pressure in mm Hg before ECMO (0-200). Worst value within 6 h. Table 4: ≤20 → −2, otherwise 0. Caller-supplied; magent does not subtract systolic minus diastolic.
- `bicarbonate_mmol_l` (number, required): Serum bicarbonate in mmol/L before ECMO (1-50). Worst value within 6 h. Table 4: ≤15 → −3, otherwise 0. magent does not measure HCO3.

## 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/save`
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": [
    {
      "acute_renal_failure": "false",
      "age": "70",
      "bicarbonate_mmol_l": "24",
      "chronic_renal_failure": "false",
      "cns_dysfunction": "false",
      "congenital_heart_disease": "false",
      "diastolic_bp_mm_hg": "35",
      "intubation_hours": "5",
      "liver_failure": "false",
      "myocarditis": "false",
      "pip_cmh2o": "25",
      "post_heart_or_lung_transplant": "false",
      "pre_ecmo_cardiac_arrest": "false",
      "pulse_pressure_mm_hg": "40",
      "refractory_vt_vf": "false",
      "weight_kg": "95"
    },
    {
      "acute_renal_failure": "false",
      "age": "70",
      "bicarbonate_mmol_l": "24",
      "chronic_renal_failure": "false",
      "cns_dysfunction": "false",
      "congenital_heart_disease": "false",
      "diastolic_bp_mm_hg": "35",
      "intubation_hours": "5",
      "liver_failure": "false",
      "myocarditis": "false",
      "pip_cmh2o": "25",
      "post_heart_or_lung_transplant": "false",
      "pre_ecmo_cardiac_arrest": "false",
      "pulse_pressure_mm_hg": "40",
      "refractory_vt_vf": "false",
      "weight_kg": "95"
    }
  ]
}
```

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

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/save",
  "items": [
    {
      "components": [
        {
          "factor": "myocarditis",
          "points": 0,
          "present": false
        },
        {
          "factor": "refractory_vt_vf",
          "points": 0,
          "present": false
        },
        {
          "factor": "post_heart_or_lung_transplant",
          "points": 0,
          "present": false
        },
        {
          "factor": "congenital_heart_disease",
          "points": 0,
          "present": false
        },
        {
          "value": 70,
          "factor": "age",
          "points": 0,
          "present": false
        },
        {
          "value": 95.0,
          "factor": "weight_kg",
          "points": 0,
          "present": false
        },
        {
          "factor": "liver_failure",
          "points": 0,
          "present": false
        },
        {
          "factor": "cns_dysfunction",
          "points": 0,
          "present": false
        },
        {
          "factor": "acute_renal_failure",
          "points": 0,
          "present": false
        },
        {
          "factor": "chronic_renal_failure",
          "points": 0,
          "present": false
        },
        {
          "value": 5.0,
          "factor": "intubation_hours",
          "points": 0,
          "present": false
        },
        {
          "value": 25.0,
          "factor": "pip_cmh2o",
          "points": 0,
          "present": false
        },
        {
          "factor": "pre_ecmo_cardiac_arrest",
          "points": 0,
          "present": false
        },
        {
          "value": 35.0,
          "factor": "diastolic_bp_mm_hg",
          "points": 0,
          "present": false
        },
        {
          "value": 40.0,
          "factor": "pulse_pressure_mm_hg",
          "points": 0,
          "present": false
        },
        {
          "value": 24.0,
          "factor": "bicarbonate_mmol_l",
          "points": 0,
          "present": false
        },
        {
          "factor": "constant",
          "points": -6,
          "present": 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": "Schmidt M, Burrell A, Roberts L, et al.",
        "doi": "10.1093/eurheartj/ehv194",
        "id": "schmidt-2015",
        "pmid": "26033984",
        "source": "Eur Heart J. 2015;36(33):2246-2256",
        "title": "Predicting survival after ECMO for refractory cardiogenic shock: the survival after veno-arterial-ECMO (SAVE)-score"
      },
      "formula": "save",
      "formula_expression": "SAVE = constant(−6) + age(18–38 → 7, 39–52 → 4, 53–62 → 3, ≥63 → 0) + weight_kg(≤65 → 1, 66–89 → 2, ≥90 → 0) + myocarditis(3) + refractory_vt_vf(2) + post_heart_or_lung_transplant(3) + congenital_heart_disease(−3) + liver_failure(−3) + cns_dysfunction(−3) + acute_renal_failure(−3) + chronic_renal_failure(−6) + intubation_hours(≤10 → 0, 11–29 → −2, ≥30 → −4) + pip_cmh2o(≤20 → 3) + pre_ecmo_cardiac_arrest(−2) + diastolic_bp_mm_hg(≥40 → 3) + pulse_pressure_mm_hg(≤20 → −2) + bicarbonate_mmol_l(≤15 → −3); diagnoses and acute organ failures may stack (Table 4 select one or more); other diagnoses 0; range −35 to 17; class I >5 → 75%, II 1–5 → 58%, III −4 to 0 → 42%, IV −9 to −5 → 30%, V ≤−10 → 18%",
      "max_score": 17,
      "score": -6,
      "min_score": -35,
      "hospital_survival_percent": 30,
      "save_class": "IV"
    },
    {
      "components": [
        {
          "factor": "myocarditis",
          "points": 0,
          "present": false
        },
        {
          "factor": "refractory_vt_vf",
          "points": 0,
          "present": false
        },
        {
          "factor": "post_heart_or_lung_transplant",
          "points": 0,
          "present": false
        },
        {
          "factor": "congenital_heart_disease",
          "points": 0,
          "present": false
        },
        {
          "value": 70,
          "factor": "age",
          "points": 0,
          "present": false
        },
        {
          "value": 95.0,
          "factor": "weight_kg",
          "points": 0,
          "present": false
        },
        {
          "factor": "liver_failure",
          "points": 0,
          "present": false
        },
        {
          "factor": "cns_dysfunction",
          "points": 0,
          "present": false
        },
        {
          "factor": "acute_renal_failure",
          "points": 0,
          "present": false
        },
        {
          "factor": "chronic_renal_failure",
          "points": 0,
          "present": false
        },
        {
          "value": 5.0,
          "factor": "intubation_hours",
          "points": 0,
          "present": false
        },
        {
          "value": 25.0,
          "factor": "pip_cmh2o",
          "points": 0,
          "present": false
        },
        {
          "factor": "pre_ecmo_cardiac_arrest",
          "points": 0,
          "present": false
        },
        {
          "value": 35.0,
          "factor": "diastolic_bp_mm_hg",
          "points": 0,
          "present": false
        },
        {
          "value": 40.0,
          "factor": "pulse_pressure_mm_hg",
          "points": 0,
          "present": false
        },
        {
          "value": 24.0,
          "factor": "bicarbonate_mmol_l",
          "points": 0,
          "present": false
        },
        {
          "factor": "constant",
          "points": -6,
          "present": 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": "Schmidt M, Burrell A, Roberts L, et al.",
        "doi": "10.1093/eurheartj/ehv194",
        "id": "schmidt-2015",
        "pmid": "26033984",
        "source": "Eur Heart J. 2015;36(33):2246-2256",
        "title": "Predicting survival after ECMO for refractory cardiogenic shock: the survival after veno-arterial-ECMO (SAVE)-score"
      },
      "formula": "save",
      "formula_expression": "SAVE = constant(−6) + age(18–38 → 7, 39–52 → 4, 53–62 → 3, ≥63 → 0) + weight_kg(≤65 → 1, 66–89 → 2, ≥90 → 0) + myocarditis(3) + refractory_vt_vf(2) + post_heart_or_lung_transplant(3) + congenital_heart_disease(−3) + liver_failure(−3) + cns_dysfunction(−3) + acute_renal_failure(−3) + chronic_renal_failure(−6) + intubation_hours(≤10 → 0, 11–29 → −2, ≥30 → −4) + pip_cmh2o(≤20 → 3) + pre_ecmo_cardiac_arrest(−2) + diastolic_bp_mm_hg(≥40 → 3) + pulse_pressure_mm_hg(≤20 → −2) + bicarbonate_mmol_l(≤15 → −3); diagnoses and acute organ failures may stack (Table 4 select one or more); other diagnoses 0; range −35 to 17; class I >5 → 75%, II 1–5 → 58%, III −4 to 0 → 42%, IV −9 to −5 → 30%, V ≤−10 → 18%",
      "max_score": 17,
      "score": -6,
      "min_score": -35,
      "hospital_survival_percent": 30,
      "save_class": "IV"
    }
  ]
}
```

## Response fields

- `formula` (string): save
- `formula_expression` (string): Exact expression used
- `score` (integer): SAVE-score, theoretical −35 to 17
- `min_score` (integer): -35
- `max_score` (integer): 17
- `save_class` (string): Schmidt 2015 Table 4 class I (>5), II (1–5), III (−4 to 0), IV (−9 to −5), or V (≤−10). A class, not a cannulation order.
- `hospital_survival_percent` (integer): Table 4 hospital survival for that class: I 75, II 58, III 42, IV 30, V 18. Score 0 is ~50% in the paper text; this field is the class percent, not a logit.
- `components` (array): Per-cell Table 4 points including constant −6
- `citation` (object): Schmidt et al. Eur Heart J 2015 citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "components": [
    {
      "factor": "myocarditis",
      "points": 0,
      "present": false
    },
    {
      "factor": "refractory_vt_vf",
      "points": 0,
      "present": false
    },
    {
      "factor": "post_heart_or_lung_transplant",
      "points": 0,
      "present": false
    },
    {
      "factor": "congenital_heart_disease",
      "points": 0,
      "present": false
    },
    {
      "value": 70,
      "factor": "age",
      "points": 0,
      "present": false
    },
    {
      "value": 95.0,
      "factor": "weight_kg",
      "points": 0,
      "present": false
    },
    {
      "factor": "liver_failure",
      "points": 0,
      "present": false
    },
    {
      "factor": "cns_dysfunction",
      "points": 0,
      "present": false
    },
    {
      "factor": "acute_renal_failure",
      "points": 0,
      "present": false
    },
    {
      "factor": "chronic_renal_failure",
      "points": 0,
      "present": false
    },
    {
      "value": 5.0,
      "factor": "intubation_hours",
      "points": 0,
      "present": false
    },
    {
      "value": 25.0,
      "factor": "pip_cmh2o",
      "points": 0,
      "present": false
    },
    {
      "factor": "pre_ecmo_cardiac_arrest",
      "points": 0,
      "present": false
    },
    {
      "value": 35.0,
      "factor": "diastolic_bp_mm_hg",
      "points": 0,
      "present": false
    },
    {
      "value": 40.0,
      "factor": "pulse_pressure_mm_hg",
      "points": 0,
      "present": false
    },
    {
      "value": 24.0,
      "factor": "bicarbonate_mmol_l",
      "points": 0,
      "present": false
    },
    {
      "factor": "constant",
      "points": -6,
      "present": 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": "Schmidt M, Burrell A, Roberts L, et al.",
    "doi": "10.1093/eurheartj/ehv194",
    "id": "schmidt-2015",
    "pmid": "26033984",
    "source": "Eur Heart J. 2015;36(33):2246-2256",
    "title": "Predicting survival after ECMO for refractory cardiogenic shock: the survival after veno-arterial-ECMO (SAVE)-score"
  },
  "formula": "save",
  "formula_expression": "SAVE = constant(−6) + age(18–38 → 7, 39–52 → 4, 53–62 → 3, ≥63 → 0) + weight_kg(≤65 → 1, 66–89 → 2, ≥90 → 0) + myocarditis(3) + refractory_vt_vf(2) + post_heart_or_lung_transplant(3) + congenital_heart_disease(−3) + liver_failure(−3) + cns_dysfunction(−3) + acute_renal_failure(−3) + chronic_renal_failure(−6) + intubation_hours(≤10 → 0, 11–29 → −2, ≥30 → −4) + pip_cmh2o(≤20 → 3) + pre_ecmo_cardiac_arrest(−2) + diastolic_bp_mm_hg(≥40 → 3) + pulse_pressure_mm_hg(≤20 → −2) + bicarbonate_mmol_l(≤15 → −3); diagnoses and acute organ failures may stack (Table 4 select one or more); other diagnoses 0; range −35 to 17; class I >5 → 75%, II 1–5 → 58%, III −4 to 0 → 42%, IV −9 to −5 → 30%, V ≤−10 → 18%",
  "max_score": 17,
  "score": -6,
  "min_score": -35,
  "hospital_survival_percent": 30,
  "save_class": "IV"
}
```

## Errors

- HTTP 400 `invalid_save`: SAVE needs Schmidt 2015 pre-ECMO cardiogenic-shock predictors in published ranges. 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

- [APACHE II](https://magentlab.com/docs/apache-ii) — Compute the Knaus 1985 APACHE II integer from 12 Acute Physiology Score items, age points, and chronic-health points.
- [mSOFA](https://magentlab.com/docs/msofa) — Compute the Grissom 2010 modified SOFA (mSOFA) total from SpO2/FiO2, caller-assigned scleral icterus or jaundice, MAP and adrenergic agents, caller-assigned GCS, and creatinine.

## 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.