Plagiarism Checker API | Proofademic Documentation

Scan text against web sources and receive a plagiarism score, matched sources, and highlighted passages.

POST /api/plagiarism/scan/

Scan text for plagiarism against web sources. Returns a plagiarism_score between 0 (original) and 1 (fully plagiarised), a verdict, the matched sources with URLs, and highlighted character ranges.

Authentication: X-API-Key header with plagiarism_checker scope

Request Parameters

Parameter	Type	Required	Description
`content`	string	Yes	Text to scan. Sent exactly as submitted — highlight offsets in the response refer to this text

Limits

Limit	Value
Minimum length	50 characters
Maximum length	25,000 words

Words are counted script-aware: whitespace-separated words for most languages, one word per character for CJK scripts. The API's count may differ slightly from a simple space-split.

Pricing

Every scan costs a flat 2 credits, regardless of text length. If the scan fails, the credits are refunded automatically.

Scans are billed per request, so retrying a request that already succeeded would normally charge again. To make retries safe, send an Idempotency-Key header (any string up to 255 characters, e.g. a UUID):

Repeating the same key with the same text within 5 minutes returns the original response — nothing is re-scanned and nothing is charged.
Repeating the same key with different text is rejected with 409 idempotency_key_reuse, so a stale key can never silently return results for the wrong text.

curl -X POST https://developer-portal.proofademic.ai/api/plagiarism/scan/ \
  -H "Content-Type: application/json" \
  -H "X-API-Key: YOUR_API_KEY" \
  -H "Idempotency-Key: 3f6c1c1e-8f2a-4a9e-9b1c-1d2e3f4a5b6c" \
  -d '{ "content": "..." }'

Example

Request

curl -X POST https://developer-portal.proofademic.ai/api/plagiarism/scan/ \
  -H "Content-Type: application/json" \
  -H "X-API-Key: YOUR_API_KEY" \
  -d '{
    "content": "The Eiffel Tower is a wrought-iron lattice tower on the Champ de Mars in Paris, France. It is named after the engineer Gustave Eiffel, whose company designed and built the tower from 1887 to 1889."
  }'

Response (200 OK)

{
  "status": "success",
  "scan_id": "scan_YYbWPwT4JHUabc12",
  "plagiarism_score": 0.99,
  "verdict": "severe_plagiarism",
  "summary": "Nearly all of the submitted text matches known sources.",
  "sources": [
    {
      "url": "https://en.wikipedia.org/wiki/Eiffel_Tower",
      "title": "Eiffel Tower - Wikipedia",
      "domain": "en.wikipedia.org",
      "similarity_score": 0.97,
      "matched_word_count": 34,
      "matched_percentage": 0.92,
      "matches": [
        {
          "submitted_range": { "start": 0, "end": 133 },
          "similarity": 0.97
        }
      ]
    }
  ],
  "highlights": [
    { "start": 0, "end": 133, "severity": "high", "source_index": 0 }
  ],
  "stats": {
    "word_count": 37,
    "input_chars": 196,
    "sentence_count": 2,
    "sources_checked": 24,
    "processing_time_ms": 3100
  },
  "execution_time": 3.4,
  "word_count": 37,
  "credits_remaining": 1998,
  "user": {
    "id": 12345
  }
}

Response Fields

Field	Type	Description
`status`	string	Always `"success"` for a completed scan
`scan_id`	string	Scan identifier — include it in support requests
`plagiarism_score`	float	0.0 (original) to 1.0 (fully plagiarised)
`verdict`	string	Classification of the score (see below)
`summary`	string	Human-readable summary of the result
`sources[]`	array	Matched sources, strongest first
`sources[].url`	string	Source URL
`sources[].title`	string	Source page title
`sources[].domain`	string	Source domain
`sources[].similarity_score`	float	How closely this source matches (0–1)
`sources[].matched_word_count`	integer	Words matched against this source
`sources[].matched_percentage`	float	Share of your text matched by this source
`sources[].matches[]`	array	Matched passages with `submitted_range` offsets
`highlights[]`	array	Character ranges to highlight in the submitted text
`highlights[].start` / `end`	integer	Offsets into your text exactly as you submitted it
`highlights[].severity`	string	`high`, `medium`, or `low`
`highlights[].source_index`	integer	Index into `sources[]` for this highlight
`stats`	object	Scan statistics (`word_count`, `input_chars`, `sentence_count`, `sources_checked`, `processing_time_ms`)
`word_count`	integer	Word count of the submitted text (script-aware)
`credits_remaining`	integer	Credit balance after this request
`user.id`	integer	Your user ID

Verdicts

Score range	Verdict
< 0.05	`original`
0.05 – 0.15	`minor_similarity`
0.15 – 0.40	`moderate_plagiarism`
0.40 – 0.70	`significant_plagiarism`
≥ 0.70	`severe_plagiarism`

Highlight severity reflects how closely each passage matches its source: high ≥ 0.85, medium ≥ 0.70, low below that.

Errors

Status	Code	Meaning
`400`	`insufficient_content`	The text does not contain enough complete sentences to scan
`400`	`max_words_exceeded`	Over the 25,000-word limit — `details` carries `limit` and `actual`
`400`	`invalid_payload`	Missing or malformed `content` (including the 50-character minimum)
`400`	`invalid_idempotency_key`	`Idempotency-Key` header longer than 255 characters
`403`	`insufficient_credits`	Not enough credits — `details` carries `credits` and `required`
`409`	`idempotency_key_reuse`	The `Idempotency-Key` was already used with different text
`503`	`service_unavailable`	Scanning temporarily unavailable — retry after the `Retry-After` header when present
`503`	`service_error`	Scan failed — credits were refunded

See Error Handling for the general error format.

Plagiarism Checker

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