# Citation anchor check

`citation-anchor-check` · version 1.0.0 · Text · free, no key needed

Check a quote anchor (exact text plus prefix/suffix) matches exactly one place in a supplied source version.

**Use when you need to: verify text quote selector anchors uniquely · check quote with prefix and suffix context in source · is this quotation ambiguous in the document.**

## Decide before calling

Read the [versioned contract](/v1/tools/citation-anchor-check/versions/1.0.0) and the supported scope below. Reuse `citation-anchor-check@1.0.0` when your input, required output and limits match it. Choose another approach for an unsupported operation.

## Explain the choice

"I can use `citation-anchor-check@1.0.0` for verify text quote selector anchors uniquely. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

## Supported

- verify text quote selector anchors uniquely
- check quote with prefix and suffix context in source
- is this quotation ambiguous in the document
- resolve exact quote anchor to code point offsets
- check that the cited sentence exists verbatim
- verify annotation anchor against supplied text version
- בדיקה שציטוט מופיע במקור פעם אחת בדיוק

## Not supported

- fetching the source or proving the supplied text is authentic
- fuzzy or approximate anchoring (no edit distance)
- case folding, whitespace collapsing or Unicode normalization
- XPath, CSS or range selectors

## Behavior

- Implements W3C Web Annotation Data Model (Recommendation 2017-02-23) 4.2.4 TextQuoteSelector, 4.2.5 TextPositionSelector; r68 supplied-text profile 1.0.0; every result carries reference_version.
- Checks only the caller-supplied text: authenticity_checked is always false. The cited (source_id, version) must be supplied (unknown_source, version_mismatch with available_versions sorted by code point).
- exact (non-empty), prefix and suffix are compared code point for code point with no normalization. Every occurrence of exact is considered, overlapping ones included; prefix must end immediately before it and suffix must start immediately after it (W3C 4.2.4). An omitted or empty prefix/suffix matches anything.
- Comparison order: exact_not_found, prefix_mismatch (exact occurs but never after prefix; observed is the text before the first occurrence), suffix_mismatch (observed is the text after the first prefix-matching occurrence), ambiguous_anchor (more than one full match), position_mismatch (claimed_start differs from the unique match).
- Positions count Unicode code points from 0 (W3C 4.2.5 convention). A valid result returns match {start, end} of the unique occurrence; match_starts lists at most the first two full-match starts.
- claimed_start is optional; omitted means no position is checked.

## Input

- `sources` (array of object, required): min items 1; max items 16
- `citation` (object, required)

## Output

- `valid` (boolean, required)
- `reason` (one of null, "unknown_source", "version_mismatch", "exact_not_found", "prefix_mismatch", "suffix_mismatch", "ambiguous_anchor", "position_mismatch", required)
- `first_discrepancy` (object or null, required)
- `match` (object or null, required)
- `authenticity_checked` (constant false, required)
- `reference_version` (constant "W3C Web Annotation Data Model (Recommendation 2017-02-23) 4.2.4 TextQuoteSelector, 4.2.5 TextPositionSelector; r68 supplied-text profile 1.0.0", required)

## Limits

- max input bytes: 1048576
- max sources: 16
- max text bytes: 524288
- max quote bytes: 16384
- max context bytes: 1024
- max label bytes: 256

## Example

Request input:

```json
{
  "sources": [
    {
      "source_id": "doc",
      "version": "2017-02-23",
      "text": "An anotation is not an annotation, but this is an anotation that has some typos."
    }
  ],
  "citation": {
    "source_id": "doc",
    "version": "2017-02-23",
    "selector": {
      "type": "TextQuoteSelector",
      "exact": "anotation",
      "prefix": "this is an ",
      "suffix": " that has some"
    }
  }
}
```

Response:

```json
{
  "result": {
    "valid": true,
    "reason": null,
    "first_discrepancy": null,
    "match": {
      "start": 50,
      "end": 59
    },
    "authenticity_checked": false,
    "reference_version": "W3C Web Annotation Data Model (Recommendation 2017-02-23) 4.2.4 TextQuoteSelector, 4.2.5 TextPositionSelector; r68 supplied-text profile 1.0.0"
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "citation-anchor-check",
  "version": "1.0.0",
  "input": {
    "sources": [
      {
        "source_id": "doc",
        "version": "2017-02-23",
        "text": "An anotation is not an annotation, but this is an anotation that has some typos."
      }
    ],
    "citation": {
      "source_id": "doc",
      "version": "2017-02-23",
      "selector": {
        "type": "TextQuoteSelector",
        "exact": "anotation",
        "prefix": "this is an ",
        "suffix": " that has some"
      }
    }
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/citation-anchor-check/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"sources":[{"source_id":"doc","version":"2017-02-23","text":"An anotation is not an annotation, but this is an anotation that has some typos."}],"citation":{"source_id":"doc","version":"2017-02-23","selector":{"type":"TextQuoteSelector","exact":"anotation","prefix":"this is an ","suffix":" that has some"}}}'
```

The machine-readable contract is at [/v1/tools/citation-anchor-check/versions/1.0.0](/v1/tools/citation-anchor-check/versions/1.0.0).

### CLI

```sh
node cli.mjs run citation-anchor-check 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [Citation passage check](/tools/citation-passage-check): Check that a cited start/end span of a supplied source version reads exactly as the quoted passage.
- [Citation batch check](/tools/citation-batch-check): Check an ordered batch of citations (span+quote or quote anchors) against supplied sources; returns the first failure.
- [Text sentence offsets](/tools/text-sentence-offsets): Return UAX #29 sentence spans as start/end offsets in code points, UTF-16 units or UTF-8 bytes, with the ending rule.
- [Chrf compute](/tools/chrf-compute): Compute exact chrF (character 6-gram F-beta, Popovic 2015) for hypothesis/reference segments, corpus and per segment.
- [Citation record normalize](/tools/citation-record-normalize): Normalize one CSL 1.0.2 citation record: NFC, whitespace, empty values, DOI wrapper, page dashes, dates; lists changes.
- [Chrf plus plus compute](/tools/chrf-plus-plus-compute): Compute exact chrF++ (character 6-grams plus word 1-2-grams, Popovic 2017) with the word tokens it scored.