HTML

html skill

Purpose: Convert a web URL or a downloaded .html/.htm/.mhtml/.webarchive into clean Markdown — with YAML frontmatter and a shared _attachments/ folder — for two consumers: (1) an Obsidian web-clipper (self-contained note), and (2) a universal HTML→Markdown step any agent workflow can call.

1. Red Flags (Anti-Rationalization)

• "I'll just paste the HTML and convert it in my head" → WRONG. The script reuses the docx-mastered turndown core (GFM tables, rowspan→flat grid) and the pdf-mastered cleaner (reader-mode, SPA-chrome strip); reimplementing in prose regresses on every edge case.
• "I'll fetch the page with curl and strip tags with regex" → WRONG. Use the script — it has SSRF protection, dual-output, sha1-deduped attachments.

Rationalization Table

2. Capabilities

• URL → Markdown via a resilient fallback ladder (--engine lite|chrome|auto|jina|remote): httpx+trafilatura lite fetch (also yields title/date/author) with retry + backoff + 429/Retry-After and a 403 → browser-UA escalation. --engine auto (default) is local-first (lite → chrome → remote last-resort); --engine jina|remote is remote-first with automatic local fallback. No single tier is a point of failure: if a remote reader is down / rate-limited / quota-exhausted, the run falls back to the next provider then to the local engines; only when every viable tier is exhausted does it fail with one typed FetchFailed (kind=all_engines_failed) carrying a details.tried trace.
• Vendor-agnostic remote reader (--engine jina|remote): the remote tier is a pluggable provider layer — jina (r.jina.ai) is the built-in default, but HTML_READER_URL / HTML_READER_PROVIDERS point it at a self-hosted Jina or any compatible reader, so resilience does not depend on any single vendor. --engine remote REQUIRES a configured provider (never a silent fall-back to jina.ai). --no-remote disables the remote tier entirely. --remote-format markdown trusts the reader's own clean Markdown; --target-selector extracts just the article block. --rate-limit throttles fetches.
• Web search → Markdown (--search "QUERY" [OUTPUT_DIR] [--max-results N]): a vendor-agnostic search provider (s.jina.ai default; HTML_SEARCH_URL / HTML_SEARCH_PROVIDERS override) returns the top results; each result URL is fetched through the same fallback ladder (so every result inherits per-result fallback) and written as one note (frontmatter query: + source:). A failed result is skipped, not fatal; a healthy zero-result search exits 0.
• Authenticated (login-gated) Chrome (--engine chrome + auth): read pages behind a login (X Articles/threads, paywalled/members, private docs) by replaying a human-minted session. Mint once: html login URL --save-state state.json (headful; 2FA ok). Then convert with --chrome-storage-state state.json (portable, server/Hermes-deployable, read-only → concurrency-safe), --chrome-cookies-file cookies.txt (cookie-only), or --chrome-user-data-dir DIR (local persistent profile). --chrome-scroll [--chrome-scroll-passes N] pulls lazy content (replies). The Chrome tier is SSRF-gated (private / off-target-public redirects refused; non-public sub-resources aborted); a stale session → auth_required. Auth is strictly opt-in — with none configured, behaviour is unchanged (no crash). The target URL + session stay local (no third party). See references/html-to-markdown.md (Hermes deploy).
• Site-specific clean-source endpoints (proactive, auto/lite): Wikipedia /wiki/<Title> → the Parsoid REST page/html endpoint (the canonical page is chrome-only and strips to empty); arXiv /abs/ or /pdf/<id> → the full-text /html/<id> rendering (PDF-only papers return an actionable "use the pdf skill" hint); HackerNoon /<slug> → /lite/<slug>.
• Empty-extraction guard: a substantial source page that converts to a near-empty body is a typed EmptyExtraction (exit 11) — never a silent exit 0 with an empty note.
• Archive → Markdown: Safari .webarchive + Chrome .mhtml (subframe-aware) + plain .html/.htm, fully offline.
• Obsidian emit: YAML frontmatter; --download-images → _attachments/ (sha1-dedup, relative links) — covers remote http(s) and content-sized inline data: images (base64/percent-encoded decoded to files; tiny icon blobs dropped); dual-output (<slug>.md + <slug>.reader.md); --reader-only emits a SINGLE <slug>.md = the reader extraction (whole-page fallback if empty) — for note pipelines.
• Math → Obsidian-native: Pandoc/MathJax \(…\) / \[…\] (and class="math" spans) → $…$ / $$…$$ with raw, un-escaped TeX, so formulas render in Obsidian/KaTeX. Escaped plain-text brackets ([word], citations) and code spans are left untouched.
• Agent step: --stdout (Markdown to stdout — inline data: blobs stripped to keep the stream clean) + --json-errors envelope.

3. Execution Mode

• Mode: script-first.
• Why this mode: HTML→Markdown is a deterministic, edge-case-heavy pipeline (fetch → clean → turndown → emit) reusing hardened docx/pdf code. Inline agent conversion regresses on tables, SPA chrome, encodings, and image handling, and has no SSRF protection.

4. Script Contract

Two operations + a combined one-shot. The skill exposes the pipeline as composable verbs so a fetched page can feed Markdown, pdf, or docx:

• python3 scripts/html fetch INPUT [OUTPUT_DIR] — OP1: download to an on-disk <slug>.html + <slug>.meta.json sidecar (+ localized _attachments/). The HTML is sanitized (file:/javascript: refs stripped) so it is safe to render; an authenticated fetch's body is written 0600. Keep the HTML to feed the pdf skill.
• python3 scripts/html md INPUT [OUTPUT_DIR] — OP2: convert a fetched artifact / local HTML / URL → Markdown. A local .html with a sibling .meta.json recovers full frontmatter from the sidecar.
• python3 scripts/html get URL (OUTPUT_PATH | --stdout) — OP3: download a URL to raw bytes, verbatim, through the same SSRF-guarded ladder. No conversion, no sanitizing, no content sniffing — the caller decides what the bytes are. Use it when you need the file itself (a PDF to hand to the pdf skill, an image, any binary): OP1/OP2 refuse a %PDF- payload on purpose, because turndown blows its call stack on binary input, and before OP3 existed a caller needing those bytes had nothing to shell out to and fell back to an unguarded raw HTTP GET. OP3 bypasses no guard — it calls _assert_safe_target + _http_get_bytes, the same two the text path uses, and omits only the content-type layer above them. Egress is direct unless HTML_PROXY is set (§5).
  • Flags: --stdout (bytes to stdout, no file — for a caller that wants a string and no temp-file lifecycle) · --max-bytes N (default 64 MiB — a finite default, unlike the conversion flags', because an unbounded arbitrary-binary download is a DoS foot-gun; the body is buffered, so this is also the memory bound) · --timeout S (per operation, default 60, in (0, 300]) · --deadline S (total wall clock, default 300, in (0, 3600]) · --retries N (0..10) · --header 'KEY: VALUE' (repeatable — needed for content negotiation, e.g. Accept: application/pdf,*/*) · --browser-ua · --json-errors.
  • ★ Wall-clock: size your subprocess(timeout=…) against --deadline, not --timeout. --timeout is per operation and bounds nothing in total: a redirect chain multiplies it by max_redirects + 1 inside every retry pass, and a slow-drip body resets the read timeout on each chunk while --max-bytes caps only SIZE. Measured: a 5-hop chain stalling below the timeout ran 2.4x the per-op budget, and a body dripping one byte per 1.6 s returned OK after 12.85 s against a 2 s timeout — time-unbounded in principle. At the shipped defaults the redirect case alone would be 60 x 6 x 4 = 1440 s. --deadline is enforced inside the ladder at every hop and every chunk, so it is a real bound; exceeding it is exit 10 with details.kind == "deadline".
  • Exit map: 0 ok · 2 usage — including a non-http(s) URL, so a caller's typo is distinguishable from a security refusal · 10 FetchFailed (SSRF refusal, redirect cap, over-cap body, deadline) · 1 internal · 141 broken pipe (--stdout only: the consumer closed the pipe and holds a PREFIX — not reported as success, so truncation stays detectable). Under exit 10 read details.kind to tell the classes apart: refused (a security block — SSRF / scheme / control chars) · deadline · otherwise a transport failure; details.max_bytes marks the over-cap case. Asserting only on the exit code cannot distinguish a security refusal from an unreachable host.
  • --browser-ua and --header 'User-Agent: …' are mutually exclusive (the header would silently win and make the flag a no-op). The artifact is written 0600.
  • On failure nothing is written, and a pre-existing OUTPUT_PATH is left untouched — not removed (get never unlinks a file it did not create). On success the write is atomic (.part + rename), so a truncated artifact the caller cannot detect is impossible.
  • Capability probe (for programmatic consumers, so an older install fails CLOSED): python3 scripts/html --help | grep -q 'html get URL'. ⚠️ A bare grep -q get always succeeds — it matches --target-selector — and html get --help exits 0 on a build without the verb too (argparse reads get as INPUT and prints the top-level help). Neither is a valid probe.
• python3 scripts/html2md.py INPUT [OUTPUT_DIR] — combined (fetch → md → delete the intermediate HTML): the classic web-clip — you get just <slug>.md (+ .reader.md) + _attachments/, no leftover HTML. This is the bare/back-compat one-shot.

Pipelines:

• download → pdf: html fetch URL out/ && python3 ../pdf/scripts/html2pdf.py out/<slug>.html out.pdf --untrusted (always pass --untrusted — it refuses file:// at the renderer, defense-in-depth over the fetch-time sanitizer). Requires html fetch ran with images (the default) so the PDF has them (pdf is offline — it never fetches remote <img>).
• download → docx: html fetch URL out/ && html md out/<slug>.html out/ && node ../docx/scripts/md2docx.js out/<slug>.md out.docx.

• Command (bare / md verb):
  • python3 scripts/html INPUT [OUTPUT_DIR] [--engine lite|chrome|auto|jina|remote] [--no-remote] [--remote-format html|markdown] [--target-selector SEL] [--chrome-storage-state PATH | --chrome-cookies-file PATH | --chrome-user-data-dir DIR] [--chrome-scroll] [--chrome-scroll-passes N] [--reader-mode|--no-reader|--reader-only] [--download-images|--no-download-images] [--attachments-dir _attachments] [--archive-frame main|N|all|auto] [--max-bytes N] [--max-images N] [--retries N] [--rate-limit REQS_PER_SEC] [--stdout] [--json-errors]
  • Search: python3 scripts/html search "QUERY" [OUTPUT_DIR] [--max-results N] [...] (or the legacy --search "QUERY").
  • Login (mint a session, headful): python3 scripts/html login URL [--save-state state.json].
  • Raw bytes (OP3): python3 scripts/html get URL (OUTPUT_PATH | --stdout) [--max-bytes N] [--timeout S] [--retries N] [--header 'KEY: VALUE'] [--browser-ua] [--json-errors].
• Environment (optional): HTML_READER_URL / HTML_READER_PROVIDERS (remote reader base(s)), HTML_READER_TOKEN (generic reader auth), JINA_API_KEY (jina quota), HTML_SEARCH_URL / HTML_SEARCH_PROVIDERS (search provider base(s)), HTML_CHROME_STORAGE_STATE / HTML_CHROME_COOKIES_FILE / HTML_CHROME_USER_DATA_DIR (Chrome auth — server-deployable secrets), HTML_SSRF_ALLOW_NETS (SSRF carve-out CIDR list — no code default; unset/empty → none; .env.example ships 198.18.0.0/15 for RFC-2544/.eth.limo mappings; 0.0.0.0/0 disables IPv4 protection), HTML_PROXY (egress proxy — the ONLY way to proxy: trust_env=False, so HTTP_PROXY/HTTPS_PROXY and the macOS System Configuration proxy are ignored. Setting it re-opens the DNS-rebinding window, see §5, and prints a one-time notice). All optional; the CLI auto-loads <skill>/.env at startup (an in-process import caller does not — call _load_skill_env() yourself). See .env.example.
• INPUT: a http(s) URL, or a local .html/.htm/.mhtml/.mht/.webarchive.
• OUTPUT_DIR: directory to write <slug>.md (+ <slug>.reader.md by default) and _attachments/ into. Omit → defaults to ./tmp/html_out/ (created on demand, in the working directory). --stdout opts into stdout mode: YAML frontmatter + whole-page Markdown (the reader variant and image files are skipped — not the reader-extracted text).
• Defaults: --engine auto, dual-output ON (--no-reader to suppress), --download-images ON (--no-download-images keeps remote URLs), attachments dir _attachments, --archive-frame main.
• Outputs: <slug>.md + <slug>.reader.md + _attachments/<sha1>.<ext>; or Markdown on stdout. <slug> is derived from the input filename / URL path (deterministic); the human title lives in frontmatter.
• Failure semantics / exit codes: 0 ok · 1 BadInput/ConvertFailed/internal · 2 usage (incl. --search+URL, --engine remote with no provider, --max-results≤0) · 3 EngineNotInstalled (Chrome explicitly requested, Playwright absent — in auto/ remote-first this is a silent fall-through, not exit 3) · 6 SelfOverwriteRefused · 10 FetchFailed (unreachable / blocked / over --max-bytes; details.kind ∈ bot_blocked/ auth_required/not_found/rate_limited/server_error/unreachable/pdf/binary/arxiv_no_html/ refused/offsite_redirect/all_engines_failed) · 11 EmptyExtraction (substantial source → near-empty body). auth_required from the chrome path = a stale/expired session (re-mint). On a total-ladder failure, details.tried lists each tier attempted + its failure kind (URL-free). --json-errors emits {v:1, error, code, type?, details?} on stderr.
• Idempotency: same input → same output filenames + deduped attachments. URL fetches reflect live content (not idempotent across server changes).

5. Safety Boundaries

• Allowed scope: only the input + the named OUTPUT_DIR (and its _attachments/). Never writes elsewhere. Exception — OP3 get: it writes the single caller-named OUTPUT_PATH, creating parent directories, and overwrites an existing file (atomically, via a sibling .part + rename, so a truncated artifact is impossible). A symlink or a directory at OUTPUT_PATH is refused (exit 2) — get never writes through a link. ⚠️ The bytes it writes are unsanitized and fully remote-controlled — every other write path in this skill runs sanitize_untrusted_html and derives its own slug. Do not point get at a path that will subsequently be rendered (html get URL page.html produces a live script/file:-bearing document on disk). The artifact is written 0600 — it is created via mkstemp and os.replaced into place, so it is never world-readable, not even in flight, and a crash cannot leave a truncated file under the caller's name.
• Image reads are confined: a malicious <img src="../../etc/passwd"> / file:///… / absolute path is refused — local image reads are confined to the input's base dir (CWE-22/73 guard).
• SSRF protection (lite path): every fetch hop (initial + redirects) is refused if it resolves to a loopback / private / link-local / cloud-metadata (169.254.169.254) address; body is streamed with a --max-bytes abort; --max-images bounds remote fetches; non-http(s) top-level INPUT is treated as a local path, never fetched.
• Remote-reader tier sends the target URL to an external service (r.jina.ai or a configured reader fetches it server-side). In --engine auto the remote tier is an automatic last-resort escalation for public targets (so a Cloudflare/anti-bot page recovers without manual intervention) — meaning a public URL may leave the machine on escalation. Guards: a private/internal/loopback/metadata target is NEVER forwarded to a reader (a public-IP gate runs before any remote request); --no-remote disables the remote tier entirely (no external egress); CR/LF/control chars in the target/query are refused (request-splitting guard). Do not point --engine jina|remote, or auto against sensitive URLs, at internal hosts you don't want proxied; use --no-remote for fully local conversion. The local hop to the reader passes the SSRF gate.
• Authenticated Chrome (TASK 024): auth replays a human-minted session (no password/2FA automation). The Chrome tier is now SSRF-gated — _assert_public_http before navigation, context-level route guard aborting non-public sub-resources/fetch/beacon, and an off-target public-redirect refusal (final origin must equal the target's eTLD+1) so a session is never carried to another site. Session files (storage_state/cookies.txt) are bearer credentials: passed by path only (never argv), required mode 0600 (group+world rejected), symlinks refused, values never logged/redacted. The target + session stay local.
• Egress is DIRECT by default (trust_env=False) so the connection pin is authoritative. The ambient environment — HTTP_PROXY/HTTPS_PROXY/ALL_PROXY, .netrc, SSL_CERT_* — is ignored; proxying is an explicit opt-in via HTML_PROXY, and setting it prints a one-time stderr notice. This is not tidiness: until it changed, the pin was decorative. Measured — pinning example.com to a blackholed 192.0.2.1 returned HTTP 200 under an ambient proxy (pin ignored) and ConnectTimeout direct (pin honoured); the machine had no proxy env vars, yet urllib.request.getproxies() still returned one from macOS System Configuration. Check yours with python3 -c "import urllib.request;print(urllib.request.getproxies())".
• Honest-scope residuals: DNS-rebinding (resolve-then-connect TOCTOU) is closed on the lite path (the connection is pinned to the validated IP) — but re-opens whenever HTML_PROXY is set, because the proxy then resolves the target itself. The per-hop _assert_public_http pre-check still runs in that mode, so it is a TOCTOU window, not an open door. ⚠️ Note also that under a fake-IP resolver (Clash/V2Ray-style, which is what the shipped HTML_SSRF_ALLOW_NETS=198.18.0.0/15 default exists for) the pin binds the synthetic address; the synthetic→real mapping lives in the proxy tool and is outside this skill's control. Rebinding also remains on the Chrome tier (Playwright manages its own sockets, and it keeps using the SYSTEM proxy regardless of HTML_PROXY); storage_state localStorage is origin-restored (readable by same-origin scripts the page loads); the login-wall heuristic is best-effort/per-site; _registrable is last-2-labels (multi-level suffixes like co.uk over-match); a reader follows its own server-side redirects. Run untrusted conversions in an egress-restricted sandbox. See references/html-to-markdown.md and docs/KNOWN_ISSUES.md (HTML2MD-10).
• No global installs: deps live in scripts/.venv + scripts/node_modules.

6. Validation Evidence

• Local verification:
  • bash scripts/install.sh — creates .venv (httpx, trafilatura), node_modules (turndown, turndown-plugin-gfm). --with-chrome adds Playwright Chromium.
  • python3 scripts/html examples/sample.html /tmp/h2m && test -s /tmp/h2m/*.md — offline file → dual Markdown + frontmatter.
  • ./scripts/.venv/bin/python -m unittest discover -s scripts/html2md/tests and -s scripts/tests — full unit + E2E suite (file/archive/url mocked + real tmp/ fixtures when present).
  • bash scripts/tests/test_e2e.sh — runs the suite + the diff -q replication gate.
• CI signal: python3 .claude/skills/skill-creator/scripts/validate_skill.py skills/html — exits 0.

7. Instructions

7.1 Clip a live URL into an Obsidian vault

python3 scripts/html https://example.com/article ./MyVault/Clips/

Produces article.md (whole) + article.reader.md (reader-extracted) + deduped _attachments/. Use --engine chrome (after install.sh --with-chrome) for JS/SPA pages.

7.2 Convert a saved archive offline

python3 scripts/html ./saved.webarchive ./out/ --archive-frame main
python3 scripts/html ./thread.mhtml ./out/ --archive-frame all

7.3 Use as a universal agent step

python3 scripts/html ./page.html --stdout --no-download-images --no-reader --json-errors

Whole-page Markdown on stdout; failures as a single-line JSON envelope.

8. Architecture & Replication (for maintainers)

html (formerly html2md) is the repo's first two-master skill (CLAUDE.md §2). It carries byte-identical replicas — do not edit them here, diff -q gated:

• web_clean/{archives,reader_mode,preprocess,dom_utils,normalize_css}.py — MASTER = pdf.
• html2md_core.js — MASTER = docx.
• _errors.py, _venv_bootstrap.py — MASTER = docx (4→5-skill).

The pdf render.py/chrome_engine.py/package __init__.py (weasyprint/playwright carriers) are never replicated; web_clean/__init__.py is an html-owned thin facade. See scripts/.AGENTS.md.

9. License

Proprietary, All Rights Reserved — see LICENSE / NOTICE. This skill embeds byte-identical copies of proprietary docx/pdf code; it is a derived work and is not Apache-2.0.

10. Resources

• references/html-to-markdown.md — decision tree (URL/archive/file; reader vs whole; lite vs chrome) + honest scope.
• examples/basic-usage.md — copy-paste examples.