`parseFrontmatter` splits each line on its first colon. That is enough to read
`name` and `description`, and it is forgiving by design — but it means a
SKILL.md whose frontmatter is not valid YAML passes every check in the linter.
The hosts that consume these skills do not share that forgiveness. Per Cursor
staff in #494, attaching a skill to a message parses its frontmatter as YAML,
and a parse failure fails the request with a generic server error and takes the
rest of the chat's context with it. So the repo could ship frontmatter that
breaks a host while CI stayed green.
Three shapes pass the current linter and are rejected by a strict parser
(confirmed against ruby's psych, each isolated by mutating only the
frontmatter of a real SKILL.md that otherwise lints clean):
description: Use this: when X colon-space: YAML reads a nested mapping
\tkey: value tab indentation is invalid YAML whitespace
description: "unterminated an unclosed quote
All three now fail with the line number and the fix. Deliberate boundaries:
a colon with no trailing space is untouched, so `https://example.com/a:b`
still passes, and a duplicate key is NOT reported because `safe_load` accepts
one — the rule tracks the parser, not taste.
This was verified once by hand against all 25 skills in the #494 thread. This
makes it a check instead of a memory.
Narrow on purpose: the repo has no package.json and therefore no YAML parser to
depend on, so this is a small set of rules aimed at the classes actually
observed to break a host, not a YAML implementation. No current frontmatter
uses block scalars or multi-line values and the check says so.
All 25 skills still pass with 0 errors, every validator exits 0, and the six
script suites are green (35 pass in skill-lint-test). Mutation-tested 4/4:
removing the call, widening the colon rule to any colon, and dropping either
the tab or the unterminated-quote rule each fail the new tests.
Refs #494
Reuse the skill linter's fence parser so inline backticks cannot hide broken references and trailing text cannot close a code fence. Cover both failures with LF and CRLF regression cases, preserving diagnostic line numbers.
stripFencedCodeBlocks matched fences with a single whole-document regex that
only recognised a column-zero backtick fence closed by a run of exactly the
same length. Three CommonMark-legal forms slipped through and their contents
were linted as prose: tilde fences, fences indented one to three spaces, and
closing fences longer than their opener. This is live on main today —
spec-driven-development's list-nested examples use indented fences, so the
linter has been reading their contents as skill text.
Replace the regex with a line scanner that tracks the opener's marker and
length, closes only on a same-marker run at least as long, treats an
unterminated fence as running to end of file (so sections after it fail
loud), and follows the CommonMark rule that a backtick fence's info string
may not contain backticks. Stripped lines become empty lines so positions
are preserved.
Add unit coverage for each form plus CRLF input, and run
scripts/lib/skill-lint-test.js in CI — it was the only test file the
workflow did not execute.
Revives the approach from #444 by @ujjwalks, which was approved and then
closed after a rebase conflict.
Closes#437
`dirName in SECTION_EXEMPT_SKILLS` walks the prototype chain, and
`constructor` satisfies KEBAB_CASE (the `*` quantifier permits a single
word). A skill directory named `constructor` therefore resolved to
Object.prototype.constructor and was silently exempt from every
required-section check — `exempt: true`, zero errors, no sections. The
bypass guard missed it for the same reason, since the resolved value is
truthy.
Both lookups now use Object.hasOwn, which is what the comment above the
allowlist already promises: "Exemptions live HERE, not in skill
frontmatter, so contributors cannot bypass the validator by editing their
own skill file."
Adds scripts/lib/skill-lint-test.js — skill-lint.js was the only
validator without a test file. Confirmed the prototype-chain test goes red
against main; the other six pass either way, so existing behaviour is
unchanged.
Scope kept to the exemption lookup: #428 already rewrites frontmatter
parsing and the cross-reference patterns, so this stays clear of both.
Two heuristic bugs in the section and trigger checks, surfaced in
addyosmani#387 and triaged by @addyosmani and @nucliweb:
Section check: content.includes('## Overview') matches headings inside
fenced code blocks and sub-headings (### Overview) because substring
matching can't distinguish prose from examples. Replace with a
line-anchored regex match against content that has had fenced code
blocks stripped, so only real top-level headings satisfy the check.
Trigger check: 'Do not use when testing' satisfied the DESCRIPTION_TRIGGER
regex because it contains 'use … when'. Add a negation pattern and reject
descriptions where the only trigger match is negated.
Verified: all 24 skills pass (output unchanged — no current skill has
either bug pattern). Crafted edge cases confirm the fixes catch both
issues. Eval suite green, rank-1 rate unchanged at 86%.
Co-authored-by: Cursor <cursoragent@cursor.com>
Per review: the policy collections (REQUIRED_SECTIONS, SECTION_EXEMPT_SKILLS,
SKILL_REF_PATTERNS, regexes) were exported by reference, so a consumer could
mutate shared state and change lint results process-wide. Export only the
linting functions; keep the policy collections private. No behavior change
(validator output byte-identical).
Split the skill validation rules out of the validate-skills.js CLI into a
shared, importable scripts/lib/skill-lint.js: a pure lintSkillContent() with
no I/O plus a thin lintSkill() file wrapper. validate-skills.js becomes a thin
CLI over the lib. No behavior change to the validator's output or exit codes;
this only makes the rules unit-testable for a follow-up test battery.
Abhishek Sharma