Placeholder values hiding as data: caller-declared sentinels and likely candidates

$0.005 USDC per call · Developer and security · POST /api/v1/sentinel-values · Id sentinel-values

Scans columns of values for sentinels. Values you declare in a dictionary (for example -1 means unknown in column age) are reported as asserted hits with their row paths. Other values that look like missing-data markers are reported separately as candidates, never asserted: the pandas default NA strings, spreadsheet error values, whitespace-only text, placeholder words, zero and epoch dates, fixed-width integer limits, -1 in an otherwise non-negative column, runs of 9s above or below every other value, and a numeric value repeated at least 3 times that lies beyond 3 interquartile ranges of the rest. For agents about to average, sum, join or load a column. It cannot know what a value means: a candidate may be real data, and 0 is never flagged.

What you get

Sentinels silently distort means, joins and date ranges. 20,000 values per $0.005 call.

Call it

Send the JSON body below to https://agents.writerslogic.com/api/v1/sentinel-values. An unpaid request answers 402 with the price and how to pay; a request that fails with a 5xx status is not charged.

curl -i -X POST https://agents.writerslogic.com/api/v1/sentinel-values \
  -H 'content-type: application/json' \
  -d '{"columns":[{"name":"age","values":[34,29,-1,41,-1,52,38,27,45,33,30,36]},{"name":"joined","values":["2021-03-04","1970-01-01","2022-07-19","N/A"]}],"dictionary":[{"column":"age","value":-1,"meaning":"unknown"}]}'

Input

FieldTypeRequiredDescription
columnsarray<object>; max 50 itemsyes
dictionaryarray<object>; max 100 itemsnoValues you know are sentinels.

Example request body

{
  "columns": [
    {
      "name": "age",
      "values": [
        34,
        29,
        -1,
        41,
        -1,
        52,
        38,
        27,
        45,
        33,
        30,
        36
      ]
    },
    {
      "name": "joined",
      "values": [
        "2021-03-04",
        "1970-01-01",
        "2022-07-19",
        "N/A"
      ]
    }
  ],
  "dictionary": [
    {
      "column": "age",
      "value": -1,
      "meaning": "unknown"
    }
  ]
}

Result

The response is { "data": ..., "_provenance": ... }. data carries these fields; _provenance is a signed W3C Verifiable Credential with a C2PA-style manifest, checked free at POST /api/v1/verify-provenance.

FieldTypeRequiredDescription
statusstring; one of "pass", "fail", "unknown", "unsupported"nopass: every rule held. fail: a rule was violated (see witnesses). unknown: the input lacks the evidence to decide. unsupported: outside what this engine covers. Missing evidence is never a pass.
columnsarray<object>no
assertedHitCountintegerno
candidateCountintegerno
witnessesarray<object>no
versionsobjectnoEvery semantic dependency of this answer (engine, tables and their as-of dates, tokenizer, calendar, rounding profile).
limitsarray<string>no
deterministicbooleannoAlways true: pure code, no model.

Pay and connect

Available through: x402 (USDC on Base), MCP. MCP clients reach it through the data-contract-kit package.

Machine-readable