POSSUM surgical audit

POSSUM

Sum Copeland 1991 Table 1 physiologic and Table 2 operative severity items, then return the published morbidity and mortality probabilities from the unrounded logits.

LIVE $0.005 USDC GET /api/calc/possum

Markdown: /docs/possum.md · Canonical: https://magentlab.com/docs/possum

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

What it computes

Sum Copeland 1991 Table 1 physiologic and Table 2 operative severity items, then return the published morbidity and mortality probabilities from the unrounded logits.

When to use

When an agent needs the original POSSUM audit scores and logits and must not substitute P-POSSUM (Whiteley), invent risk classes, or issue operative consent.

When not to use

Not a medical device. Not a diagnosis. Not an operative-consent tool. magent does not examine the patient.
Copeland 1991 Tables 1-2 and the original morbidity and mortality logits only. This is not P-POSSUM (Whiteley).
Age has no 8-point cell; ECG, multiple_procedures, and mode_of_surgery have no 2-point cell. magent does not cap the integer below the sum of published item maxima.
Each band is caller-assigned. magent does not interpret an ECG tracing or classify an operative note.
Estimated percents are population audit probabilities from the unrounded logits, not an individual outcome.

Formula

physiologic_score = sum of 12 Copeland 1991 Table 1 items (1/2/4/8; age has no 8, ECG has no 2); operative_score = sum of 6 Table 2 items (1/2/4/8; multiple_procedures and mode_of_surgery have no 2); ln[R/(1-R)] morbidity = -5.91 + 0.16*physiologic_score + 0.19*operative_score; ln[R/(1-R)] mortality = -7.04 + 0.13*physiologic_score + 0.16*operative_score; estimated_morbidity_percent and estimated_mortality_percent = 100 * exp(logit)/(1+exp(logit)) from the unrounded logit

Citation

Title: POSSUM: a scoring system for surgical audit
Authors: Copeland GP, Jones D, Walters M
Source: Br J Surg. 1991;78(3):355-360
DOI: 10.1002/bjs.1800780327

Worked example

All lowest Table 1 and Table 2 poles

Given: age_years=50blood_loss_ml=50cardiac=no_failureecg=normalgcs=15hemoglobin_g_dl=14malignancy=nonemode_of_surgery=electivemultiple_procedures=oneoperative_severity=minorperitoneal_soiling=nonepotassium_mmol_l=4.0pulse=70respiratory=no_dyspneasodium_mmol_l=140systolic_bp_mm_hg=120urea_mmol_l=5wbc_k_ul=8

Each of 12 Table 1 items is 1 (age 50, no_failure, no_dyspnea, SBP 120, pulse 70, GCS 15, Hb 14, WBC 8, urea 5, Na 140, K 4.0, ECG normal)
Each of 6 Table 2 items is 1 (minor, one procedure, blood loss 50, soiling none, malignancy none, elective)
physiologic_score = 12; operative_score = 6
morbidity logit = -5.91 + 0.16×12 + 0.19×6 = -2.85
mortality logit = -7.04 + 0.13×12 + 0.16×6 = -4.52
percents = 100 × exp(logit)/(1+exp(logit)) from the unrounded logits

All Table 1 and Table 2 item maxima

Given: age_years=80blood_loss_ml=1500cardiac=raised_jvp_or_cardiomegalyecg=other_abnormal_or_ectopics_or_q_st_tgcs=5hemoglobin_g_dl=8malignancy=distant_metastasesmode_of_surgery=immediate_lt_2hmultiple_procedures=more_than_twooperative_severity=major_plusperitoneal_soiling=free_bowel_pus_bloodpotassium_mmol_l=2.5pulse=30respiratory=rest_or_fibrosis_consolidationsodium_mmol_l=120systolic_bp_mm_hg=80urea_mmol_l=20wbc_k_ul=2

Age ≥71 → 4; the other 11 Table 1 items are 8
Each of 6 Table 2 items is 8
physiologic_score = 92; operative_score = 48
percents from the unrounded Copeland logits

Also searched as

POSSUM
Copeland POSSUM
physiologic and operative severity score
surgical audit score
POSSUM morbidity mortality
Copeland surgical score
POSSUM physiologic score

Try

Opens the live endpoint. Unpaid browser requests show the paywall; agents should send Accept: application/json.

/api/calc/possum?age_years=50&cardiac=no_failure&respiratory=no_dyspnea&systolic_bp_mm_hg=120&pulse=70&gcs=15&hemoglobin_g_dl=14&wbc_k_ul=8&urea_mmol_l=5&sodium_mmol_l=140&potassium_mmol_l=4.0&ecg=normal&operative_severity=minor&multiple_procedures=one&blood_loss_ml=50&peritoneal_soiling=none&malignancy=none&mode_of_surgery=elective

Full URL: https://api.magentlab.com/api/calc/possum?age_years=50&cardiac=no_failure&respiratory=no_dyspnea&systolic_bp_mm_hg=120&pulse=70&gcs=15&hemoglobin_g_dl=14&wbc_k_ul=8&urea_mmol_l=5&sodium_mmol_l=140&potassium_mmol_l=4.0&ecg=normal&operative_severity=minor&multiple_procedures=one&blood_loss_ml=50&peritoneal_soiling=none&malignancy=none&mode_of_surgery=elective

Call

Expect HTTP 402 until you retry with PAYMENT-SIGNATURE. Incomplete query params return HTTP 400 before any quote or charge.

curl -i -H "Accept: application/json" "https://api.magentlab.com/api/calc/possum?age_years=50&cardiac=no_failure&respiratory=no_dyspnea&systolic_bp_mm_hg=120&pulse=70&gcs=15&hemoglobin_g_dl=14&wbc_k_ul=8&urea_mmol_l=5&sodium_mmol_l=140&potassium_mmol_l=4.0&ecg=normal&operative_severity=minor&multiple_procedures=one&blood_loss_ml=50&peritoneal_soiling=none&malignancy=none&mode_of_surgery=elective"

Parameters

Name	Type	Required	Description
`age_years`	integer	required	Age in years, integer 16-120 (Copeland 1991 Table 1). ≤60 → 1; 61-70 → 2; ≥71 → 4. No 8-point cell.
`cardiac`	string	required · no_failure, diuretic_digoxin_antianginal_or_hypertensive, peripheral_edema_warfarin_or_borderline_cardiomegaly, raised_jvp_or_cardiomegaly	Copeland 1991 cardiac signs as assigned by the caller: no_failure (1); diuretic_digoxin_antianginal_or_hypertensive (2); peripheral_edema_warfarin_or_borderline_cardiomegaly (4); raised_jvp_or_cardiomegaly (8). magent does not examine the patient.
`respiratory`	string	required · no_dyspnea, exertional_or_mild_coad, limiting_or_moderate_coad, rest_or_fibrosis_consolidation	Copeland 1991 respiratory history as assigned by the caller: no_dyspnea (1); exertional_or_mild_coad (2); limiting_or_moderate_coad (4); rest_or_fibrosis_consolidation (8). magent does not examine the patient.
`systolic_bp_mm_hg`	number	required	Systolic blood pressure in mm Hg (20-300). 110-130 → 1; 100-109 or 131-170 → 2; 90-99 or ≥171 → 4; ≤89 → 8. magent does not measure blood pressure.
`pulse`	integer	required	Pulse in beats/min, integer 20-250. 50-80 → 1; 81-100 → 2; 40-49 or 101-120 → 4; ≤39 or ≥121 → 8. magent does not measure pulse.
`gcs`	integer	required	Glasgow Coma Scale total as assigned by the caller, integer 3-15. 15 → 1; 12-14 → 2; 9-11 → 4; ≤8 → 8. magent does not examine the patient.
`hemoglobin_g_dl`	number	required	Haemoglobin in g/dL (3-25). 13-16 → 1; 11.5-12.9 or 16.1-17.0 → 2; 10.0-11.4 or 17.1-18.0 → 4; ≤9.9 or ≥18.1 → 8.
`wbc_k_ul`	number	required	White cell count in ×10^9/L (0.1-100). 4.0-10.0 → 1; 10.1-20.0 or 3.1-3.9 → 2; ≥20.1 → 4; ≤3.0 → 8. Table 1 lists 3.1-4.0 on the 2-point cell; 4.0 is scored in the 1-point band.
`urea_mmol_l`	number	required	Serum urea in mmol/L (0.5-80). ≤7.5 → 1; 7.6-10.0 → 2; 10.1-15.0 → 4; ≥15.1 → 8.
`sodium_mmol_l`	number	required	Serum sodium in mmol/L (90-200). ≥136 → 1; 131-135 → 2; 126-130 → 4; ≤125 → 8.
`potassium_mmol_l`	number	required	Serum potassium in mmol/L (1-12). 3.5-5.0 → 1; 3.2-3.4 or 5.1-5.3 → 2; 2.9-3.1 or 5.4-5.9 → 4; ≤2.8 or ≥6.0 → 8.
`ecg`	string	required · normal, atrial_fibrillation_60_90, other_abnormal_or_ectopics_or_q_st_t	Copeland 1991 electrocardiogram as assigned by the caller: normal (1); atrial_fibrillation_60_90 (4); other_abnormal_or_ectopics_or_q_st_t (8). No 2-point cell. magent does not interpret a tracing.
`operative_severity`	string	required · minor, moderate, major, major_plus	Copeland 1991 Table 2 operative severity as assigned by the caller: minor (1); moderate (2); major (4); major_plus (8). magent does not classify an operative note.
`multiple_procedures`	string	required · one, two, more_than_two	Number of procedures as assigned by the caller: one (1); two (4); more_than_two (8). No 2-point cell.
`blood_loss_ml`	number	required	Total blood loss in mL (0-20000). ≤100 → 1; 101-500 → 2; 501-999 → 4; ≥1000 → 8. Table 2 writes <100 then 101-500; 100 mL is scored with the lowest band.
`peritoneal_soiling`	string	required · none, minor_serous, local_pus, free_bowel_pus_blood	Copeland 1991 peritoneal soiling as assigned by the caller: none (1); minor_serous (2); local_pus (4); free_bowel_pus_blood (8). magent does not examine the patient.
`malignancy`	string	required · none, primary_only, nodal_metastases, distant_metastases	Copeland 1991 presence of malignancy as assigned by the caller: none (1); primary_only (2); nodal_metastases (4); distant_metastases (8). magent does not diagnose.
`mode_of_surgery`	string	required · elective, emergency_resuscitation_gt_2h_or_lt_24h, immediate_lt_2h	Copeland 1991 mode of surgery as assigned by the caller: elective (1); emergency_resuscitation_gt_2h_or_lt_24h (4); immediate_lt_2h (8). No 2-point cell.

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.

POST /api/calc/possum Max 25 unit_amount + extra_item_amount * (n - 1) extra $0.002 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 (fixture)

{
  "items": [
    {
      "age_years": "50",
      "blood_loss_ml": "50",
      "cardiac": "no_failure",
      "ecg": "normal",
      "gcs": "15",
      "hemoglobin_g_dl": "14",
      "malignancy": "none",
      "mode_of_surgery": "elective",
      "multiple_procedures": "one",
      "operative_severity": "minor",
      "peritoneal_soiling": "none",
      "potassium_mmol_l": "4.0",
      "pulse": "70",
      "respiratory": "no_dyspnea",
      "sodium_mmol_l": "140",
      "systolic_bp_mm_hg": "120",
      "urea_mmol_l": "5",
      "wbc_k_ul": "8"
    },
    {
      "age_years": "50",
      "blood_loss_ml": "50",
      "cardiac": "no_failure",
      "ecg": "normal",
      "gcs": "15",
      "hemoglobin_g_dl": "14",
      "malignancy": "none",
      "mode_of_surgery": "elective",
      "multiple_procedures": "one",
      "operative_severity": "minor",
      "peritoneal_soiling": "none",
      "potassium_mmol_l": "4.0",
      "pulse": "70",
      "respiratory": "no_dyspnea",
      "sodium_mmol_l": "140",
      "systolic_bp_mm_hg": "120",
      "urea_mmol_l": "5",
      "wbc_k_ul": "8"
    }
  ]
}

Open bulk paywall →

Opens a two-item fixture on the API host. Unpaid browsers get the same MetaMask paywall as GET; Pay retries POST with those items.

Example 200 (fixture)

{
  "count": 2,
  "path": "/api/calc/possum",
  "items": [
    {
      "components": [
        {
          "value": 50,
          "factor": "age_years",
          "points": 1,
          "present": true
        },
        {
          "value": "no_failure",
          "factor": "cardiac",
          "points": 1,
          "present": true
        },
        {
          "value": "no_dyspnea",
          "factor": "respiratory",
          "points": 1,
          "present": true
        },
        {
          "value": 120.0,
          "factor": "systolic_bp_mm_hg",
          "points": 1,
          "present": true
        },
        {
          "value": 70,
          "factor": "pulse",
          "points": 1,
          "present": true
        },
        {
          "value": 15,
          "factor": "gcs",
          "points": 1,
          "present": true
        },
        {
          "value": 14.0,
          "factor": "hemoglobin_g_dl",
          "points": 1,
          "present": true
        },
        {
          "value": 8.0,
          "factor": "wbc_k_ul",
          "points": 1,
          "present": true
        },
        {
          "value": 5.0,
          "factor": "urea_mmol_l",
          "points": 1,
          "present": true
        },
        {
          "value": 140.0,
          "factor": "sodium_mmol_l",
          "points": 1,
          "present": true
        },
        {
          "value": 4.0,
          "factor": "potassium_mmol_l",
          "points": 1,
          "present": true
        },
        {
          "value": "normal",
          "factor": "ecg",
          "points": 1,
          "present": true
        },
        {
          "value": "minor",
          "factor": "operative_severity",
          "points": 1,
          "present": true
        },
        {
          "value": "one",
          "factor": "multiple_procedures",
          "points": 1,
          "present": true
        },
        {
          "value": 50.0,
          "factor": "blood_loss_ml",
          "points": 1,
          "present": true
        },
        {
          "value": "none",
          "factor": "peritoneal_soiling",
          "points": 1,
          "present": true
        },
        {
          "value": "none",
          "factor": "malignancy",
          "points": 1,
          "present": true
        },
        {
          "value": "elective",
          "factor": "mode_of_surgery",
          "points": 1,
          "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": "Copeland GP, Jones D, Walters M",
        "doi": "10.1002/bjs.1800780327",
        "id": "copeland-1991",
        "pmid": "2021856",
        "source": "Br J Surg. 1991;78(3):355-360",
        "title": "POSSUM: a scoring system for surgical audit"
      },
      "formula": "possum",
      "formula_expression": "physiologic_score = sum of 12 Copeland 1991 Table 1 items (1/2/4/8; age has no 8, ECG has no 2); operative_score = sum of 6 Table 2 items (1/2/4/8; multiple_procedures and mode_of_surgery have no 2); ln[R/(1-R)] morbidity = -5.91 + 0.16*physiologic_score + 0.19*operative_score; ln[R/(1-R)] mortality = -7.04 + 0.13*physiologic_score + 0.16*operative_score; estimated_morbidity_percent and estimated_mortality_percent = 100 * exp(logit)/(1+exp(logit)) from the unrounded logit",
      "estimated_morbidity_percent": 5.47,
      "estimated_mortality_percent": 1.08,
      "morbidity_logit": -2.85,
      "mortality_logit": -4.52,
      "operative_score": 6,
      "physiologic_score": 12
    },
    {
      "components": [
        {
          "value": 50,
          "factor": "age_years",
          "points": 1,
          "present": true
        },
        {
          "value": "no_failure",
          "factor": "cardiac",
          "points": 1,
          "present": true
        },
        {
          "value": "no_dyspnea",
          "factor": "respiratory",
          "points": 1,
          "present": true
        },
        {
          "value": 120.0,
          "factor": "systolic_bp_mm_hg",
          "points": 1,
          "present": true
        },
        {
          "value": 70,
          "factor": "pulse",
          "points": 1,
          "present": true
        },
        {
          "value": 15,
          "factor": "gcs",
          "points": 1,
          "present": true
        },
        {
          "value": 14.0,
          "factor": "hemoglobin_g_dl",
          "points": 1,
          "present": true
        },
        {
          "value": 8.0,
          "factor": "wbc_k_ul",
          "points": 1,
          "present": true
        },
        {
          "value": 5.0,
          "factor": "urea_mmol_l",
          "points": 1,
          "present": true
        },
        {
          "value": 140.0,
          "factor": "sodium_mmol_l",
          "points": 1,
          "present": true
        },
        {
          "value": 4.0,
          "factor": "potassium_mmol_l",
          "points": 1,
          "present": true
        },
        {
          "value": "normal",
          "factor": "ecg",
          "points": 1,
          "present": true
        },
        {
          "value": "minor",
          "factor": "operative_severity",
          "points": 1,
          "present": true
        },
        {
          "value": "one",
          "factor": "multiple_procedures",
          "points": 1,
          "present": true
        },
        {
          "value": 50.0,
          "factor": "blood_loss_ml",
          "points": 1,
          "present": true
        },
        {
          "value": "none",
          "factor": "peritoneal_soiling",
          "points": 1,
          "present": true
        },
        {
          "value": "none",
          "factor": "malignancy",
          "points": 1,
          "present": true
        },
        {
          "value": "elective",
          "factor": "mode_of_surgery",
          "points": 1,
          "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": "Copeland GP, Jones D, Walters M",
        "doi": "10.1002/bjs.1800780327",
        "id": "copeland-1991",
        "pmid": "2021856",
        "source": "Br J Surg. 1991;78(3):355-360",
        "title": "POSSUM: a scoring system for surgical audit"
      },
      "formula": "possum",
      "formula_expression": "physiologic_score = sum of 12 Copeland 1991 Table 1 items (1/2/4/8; age has no 8, ECG has no 2); operative_score = sum of 6 Table 2 items (1/2/4/8; multiple_procedures and mode_of_surgery have no 2); ln[R/(1-R)] morbidity = -5.91 + 0.16*physiologic_score + 0.19*operative_score; ln[R/(1-R)] mortality = -7.04 + 0.13*physiologic_score + 0.16*operative_score; estimated_morbidity_percent and estimated_mortality_percent = 100 * exp(logit)/(1+exp(logit)) from the unrounded logit",
      "estimated_morbidity_percent": 5.47,
      "estimated_mortality_percent": 1.08,
      "morbidity_logit": -2.85,
      "mortality_logit": -4.52,
      "operative_score": 6,
      "physiologic_score": 12
    }
  ]
}

Response

Field	Type	Description
`formula`	string	possum
`formula_expression`	string	Copeland 1991 Tables 1-2 and logits
`physiologic_score`	integer	Sum of 12 Table 1 items (min 12; item maxima sum to 92)
`operative_score`	integer	Sum of 6 Table 2 items (min 6; item maxima sum to 48)
`morbidity_logit`	number	Copeland 1991 morbidity logit, 2 decimal places
`mortality_logit`	number	Copeland 1991 mortality logit, 2 decimal places
`estimated_morbidity_percent`	number	100 * exp(logit)/(1+exp(logit)) from the unrounded morbidity logit, 2 decimals. An audit probability, not a diagnosis.
`estimated_mortality_percent`	number	100 * exp(logit)/(1+exp(logit)) from the unrounded mortality logit, 2 decimals. An audit probability, not operative consent.
`components`	array	Eighteen Table 1 and Table 2 rows
`citation`	object	Copeland 1991 citation
`disclaimer`	string	Not-a-device notice

Example JSON

Machine form of the same example. Frozen fixture. Not a live lookup.

{
  "components": [
    {
      "value": 50,
      "factor": "age_years",
      "points": 1,
      "present": true
    },
    {
      "value": "no_failure",
      "factor": "cardiac",
      "points": 1,
      "present": true
    },
    {
      "value": "no_dyspnea",
      "factor": "respiratory",
      "points": 1,
      "present": true
    },
    {
      "value": 120.0,
      "factor": "systolic_bp_mm_hg",
      "points": 1,
      "present": true
    },
    {
      "value": 70,
      "factor": "pulse",
      "points": 1,
      "present": true
    },
    {
      "value": 15,
      "factor": "gcs",
      "points": 1,
      "present": true
    },
    {
      "value": 14.0,
      "factor": "hemoglobin_g_dl",
      "points": 1,
      "present": true
    },
    {
      "value": 8.0,
      "factor": "wbc_k_ul",
      "points": 1,
      "present": true
    },
    {
      "value": 5.0,
      "factor": "urea_mmol_l",
      "points": 1,
      "present": true
    },
    {
      "value": 140.0,
      "factor": "sodium_mmol_l",
      "points": 1,
      "present": true
    },
    {
      "value": 4.0,
      "factor": "potassium_mmol_l",
      "points": 1,
      "present": true
    },
    {
      "value": "normal",
      "factor": "ecg",
      "points": 1,
      "present": true
    },
    {
      "value": "minor",
      "factor": "operative_severity",
      "points": 1,
      "present": true
    },
    {
      "value": "one",
      "factor": "multiple_procedures",
      "points": 1,
      "present": true
    },
    {
      "value": 50.0,
      "factor": "blood_loss_ml",
      "points": 1,
      "present": true
    },
    {
      "value": "none",
      "factor": "peritoneal_soiling",
      "points": 1,
      "present": true
    },
    {
      "value": "none",
      "factor": "malignancy",
      "points": 1,
      "present": true
    },
    {
      "value": "elective",
      "factor": "mode_of_surgery",
      "points": 1,
      "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": "Copeland GP, Jones D, Walters M",
    "doi": "10.1002/bjs.1800780327",
    "id": "copeland-1991",
    "pmid": "2021856",
    "source": "Br J Surg. 1991;78(3):355-360",
    "title": "POSSUM: a scoring system for surgical audit"
  },
  "formula": "possum",
  "formula_expression": "physiologic_score = sum of 12 Copeland 1991 Table 1 items (1/2/4/8; age has no 8, ECG has no 2); operative_score = sum of 6 Table 2 items (1/2/4/8; multiple_procedures and mode_of_surgery have no 2); ln[R/(1-R)] morbidity = -5.91 + 0.16*physiologic_score + 0.19*operative_score; ln[R/(1-R)] mortality = -7.04 + 0.13*physiologic_score + 0.16*operative_score; estimated_morbidity_percent and estimated_mortality_percent = 100 * exp(logit)/(1+exp(logit)) from the unrounded logit",
  "estimated_morbidity_percent": 5.47,
  "estimated_mortality_percent": 1.08,
  "morbidity_logit": -2.85,
  "mortality_logit": -4.52,
  "operative_score": 6,
  "physiologic_score": 12
}

Client errors (HTTP 400)

Invalid params return 400 without charge. Shared HTTP 402 and 503 meanings: Payments.

HTTP	Code	When
400	`invalid_possum`	POSSUM needs Copeland 1991 physiologic and operative severity items in published ranges. Returned before settlement; you are not charged.
400	`invalid_items`	POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
400	`invalid_item_count`	items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
400	`invalid_item`	each items entry must be a JSON object Returned before settlement; you are not charged.

Related tools

Surgical Apgar — Compute the Gawande 2007 intraoperative Surgical Apgar score from estimated blood loss, lowest mean arterial pressure, and lowest heart rate.
APACHE II — Compute the Knaus 1985 APACHE II integer from 12 Acute Physiology Score items, age points, and chronic-health points.

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. Unpaid valid requests return HTTP 402 with a base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote: retry the same PAYMENT-SIGNATURE. Full handshake and shared payment errors: Payments. Stdio MCP: /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.