llm-security-commons/spec/conformance-corpus.md

Conformance corpus

Status: normative. This document defines how the files under conformance/ are to be read. Where it disagrees with any informative document in docs/, this wins.

RFC 2119 language is used deliberately: MUST, MUST NOT, SHOULD, MAY.

1. What a case is

A case is a directory under conformance/ holding exactly two files:

conformance/<case-id>/input.txt        the exact bytes to scan
conformance/<case-id>/expected.json    the findings a conforming runtime produces

A runtime claiming conformance MUST run every case. It MUST NOT skip a case because its engine rejects the pattern behind it — a silently skipped case is an invisible false negative, which is the failure mode this corpus exists to catch. A case that cannot be run MUST be reported as an error, not as a pass.

2. input.txt is bytes, not text

input.txt holds the input verbatim, UTF-8 encoded. A runtime MUST read it as bytes and MUST NOT strip, trim, normalise or re-encode anything before scanning.

There is no trailing newline. A trailing newline would be part of the input, and no case wants one. Two of the current cases carry characters that are invisible on screen — a zero-width space and a Cyrillic homoglyph — so an editor that "cleans up" a fixture can change what it tests without changing how it looks. For that reason every expected.json records the input's byte length and SHA-256, and a runtime SHOULD verify both before scanning. A digest mismatch means the fixture has been altered; the result of scanning it means nothing.

3. expected.json

{
  "case_id": "hybrid-xss__script-tag",
  "input": { "file": "input.txt", "bytes": 24, "sha256": "…" },
  "scope": ["lexicon/injection-lexicon.json"],
  "match": "exact-within-scope",
  "findings": [{ "id": "hybrid-xss:script-tag" }],
  "observed_out_of_scope": { "llm_ingestion_guard": ["active:raw-html"] }
}

Field	Normative?	Meaning
case_id	yes	Equals the directory name.
input	yes	Integrity of the input file. See §2.
scope	yes	Which commons data files this case constrains. See §4.
match	yes	How findings is to be compared. See §4.
findings	yes	The expected findings, named by commons pattern id.
observed_out_of_scope	no — informative	What a named runtime was measured emitting outside scope. Evidence, never expectation. See §5.

A finding carries an id and nothing else. Severity, OWASP anchor and human label are properties of the pattern, published once in lexicon/injection-lexicon.json and looked up there by id. They MUST NOT be restated in a fixture: a value written in two places is a value that will eventually disagree with itself.

Fixture files carry no individual version field, which is the one place this repository's "every JSON file has a top-level version" convention does not apply. The corpus is versioned as a whole in conformance/manifest.json. The exception is deliberate and stated here rather than left to be discovered.

4. exact-within-scope

This is the only match value defined in this version, and it means:

Restricted to findings whose id belongs to a data file named in scope, the runtime's finding set MUST equal findings exactly. Findings outside that scope MUST be ignored by the comparison — neither required nor forbidden.

So a runtime MUST NOT raise a lexicon finding this case does not list, and MUST raise every one it does. Whether the same runtime also flags the input as active content, as a carrier, or as anything else is not this case's business.

The scoping is what makes the exactness safe. The two seeding runtimes do not implement the same set of tables — one has no active-content table at all — so a whole-report comparison would fail for reasons that have nothing to do with the pattern under test. Scoping the comparison to one published table asks a question both can answer.

The exactness is what makes the corpus worth running. A corpus that only checks that the expected finding is present is passed by a runtime that flags everything.

A future case MAY declare a different scope or a different match. A runtime MUST reject a match value it does not implement rather than degrade to a weaker comparison.

5. observed_out_of_scope is evidence, not expectation

This block records what a named runtime, at a named commit, was measured emitting outside the case's scope. It exists so that a reader can see what was left out of the contract instead of having to trust that nothing was.

A runtime MUST NOT be failed for disagreeing with it, and MUST NOT be required to reproduce it.

Absence of a runtime's key means unmeasured, not measured-empty. The current corpus carries no llm_security key anywhere, because that runtime was measured through its injection-scanner entry point, which cannot emit an out-of-scope finding by construction. Reading that absence as "this runtime emits nothing else" would be a claim nobody made.

6. Case ids

case_id  = pattern_id with ":" replaced by "__"
pattern_id = case_id with "__" replaced by ":"

: is not a legal filename character on Windows, and fork-and-own is a supported use of this repository, so the id space cannot reach the filesystem unchanged. __ does not occur anywhere in the ratified id space, so the transform is one-to-one — verified collision-free across all cases rather than assumed.

A case id is a stable identifier. Changing one is a BREAKING change and requires a major bump of the corpus version, exactly like changing a pattern id. Consumers name cases in their own test suites; a renamed case is a silently disappeared test.

7. When a runtime and a fixture disagree

The fixture is ground truth. A runtime that disagrees is wrong — unless the fixture itself is proven wrong, in which case the fixture changes in its own commit, with the reason written down, and the corpus version is bumped.

This ordering is the whole point of the repository. Two implementations that return different verdicts on the same input are not holding different opinions; one of them has a bug.

8. What conformance does and does not prove

Passing this corpus proves that a runtime agrees with the other runtimes that pass it, on these inputs. It does not prove the fixtures are right. A wrong expected.json makes every passing runtime wrong in the same way, which is a real failure mode and not a rhetorical one — it is why each case records how it was produced.

Nor is the corpus a coverage claim. It covers the pattern tables named in conformance/manifest.json under scope_covered, and the tables under scope_planned are named there precisely so that their absence is visible rather than inferred.