Skill v1.0.2

name: cp-skill-snapshot-web description: Snapshot a URL into the local kb/sources/.snapshots/ cache, routing GitHub, X/Twitter, PDF, and ordinary web sources to the appropriate capture path. type: types/instruction.md user-invocable: true allowed-tools: Read, Write, Grep, Glob, Bash context: fork model: sonnet argument-hint: "[url] [reobserve] — URL to snapshot (web page, PDF, GitHub issue/PR, or X/Twitter post); add reobserve to capture a changed source again" metadata: version: "1.0.2"

Intent and execution authority

Preserve a faithful local reading copy of the requested source so later ingest can analyse it against an exact-file checksum.

The tools and commands below are supported routes, not an exhaustive list of permitted methods. Choose another available tool or write local extraction code when needed to capture the requested content faithfully. A failed tool is not by itself a reason to abandon the capture. Requirements imposed by a caller, such as a version-pinned PDF capture, still bind.

Done means: the requested content, not merely its page shell, is saved with accurate source identity, capture method and scope, and its exact Markdown-file SHA-256 is reported. Preserve relevant links and footnotes. If only part of the requested content is available, disclose the missing part and label the scope; do not silently substitute an abstract, surrounding page, or commentary.

Binding boundaries: keep captures local and ignored, never overwrite an existing observation, do not fabricate or analyse source content, and copy the captured body locally rather than re-emitting it through model output. Do not install software, bypass access controls, or execute code supplied by the page. Return to the user when completion needs new permission or when available evidence cannot establish source identity or capture fidelity.

EXECUTE NOW

Target: $ARGUMENTS

If no URL provided, ask the user for one.

If URL provided, start Step 1 immediately.

START NOW.

Step 1: Verify Local Storage and Check for Duplicates

Keep the provided URL as source_url. The request is a re-observation when it says reobserve or asks to capture a source again because it changed since its existing capture. Verify that kb/sources/.snapshots/ is ignored by the project. The shipped scaffold does this through kb/sources/.gitignore. If the directory is not ignored, stop before writing and report the missing rule.

For PDF and ordinary web captures, keep temporary downloads, extracted bodies, and assembly files in a unique directory under kb/reports/cache/snapshot-web/. Verify that payloads there are ignored before writing; stop and report a missing ignore rule. The final snapshot still belongs in kb/sources/.snapshots/.

Use Grep to search for an exact frontmatter source: {source_url} in existing Markdown files in kb/sources/.snapshots/. For a re-observation, an existing capture is expected: continue, and write the new capture under a distinct basename as described under Step 2 and slug below. Never overwrite or edit the existing capture; its ingest pins its bytes. Otherwise, if found, compute the SHA-256 of the exact file bytes, tell the user, and stop:

Already snapshotted: kb/sources/.snapshots/{filename}

SHA-256: {64-character lowercase checksum}

Step 2: Route by URL Type

Detect the source_url type and branch:

• GitHub issue/PR (github.com/.../issues/N or github.com/.../pull/N) → Step 2a
• X/Twitter (x.com/.../status/... or twitter.com/.../status/...) → Step 2b
• arXiv abstract page (arxiv.org/abs/...) → Step 2c
• PDF (URL ends in .pdf, or arxiv.org/pdf/) → Step 2c
• Everything else → Step 2d

Step 2a: GitHub Issue/PR

Run:

commonplace-github-snapshot "{source_url}"

For a re-observation, add --reobserve: the command skips the duplicate check and names the new capture with the capture date.

Parse either the Snapshot saved: or Already snapshotted: line from the output to get the file path. Tell the user and stop — the script handles metadata, formatting, and saving. If it fails, use Step 3.

Step 2b: X/Twitter Post

Run:

commonplace-x-snapshot "{source_url}"

For a re-observation, add --reobserve: the command skips the duplicate check and names the new capture with the capture date.

Parse either the Snapshot saved: or Already snapshotted: line from the output to get the file path. Tell the user and stop — the script handles metadata, formatting, and saving. If it fails, use Step 3.

Step 2c: Resolve and Fetch PDF

Verify that the PDF capture prerequisites are available:

command -v curl
command -v pdfinfo
command -v pdftotext

If a command is missing, use another available tool that preserves the paper's content, or go to Step 3. Do not install prerequisites.

Set pdf_url:

• For an arXiv abstract URL, replace /abs/ with /pdf/ and discard any query string or fragment. Preserve an explicit terminal version such as v1. If the abstract URL has no terminal version, leave the PDF URL unversioned so arXiv serves the latest paper version. For example, https://arxiv.org/abs/2606.03979 becomes https://arxiv.org/pdf/2606.03979. Do not route the abstract page through ordinary HTML capture.
• For an existing PDF URL, use source_url unchanged.

Create the temporary directory and retain the printed path as {snapshot_tmp}:

set -e
mkdir -p kb/reports/cache/snapshot-web
snapshot_tmp=$(mktemp -d kb/reports/cache/snapshot-web/capture.XXXXXX)
printf 'Snapshot temp: %s\n' "$snapshot_tmp"

Download in a separate invocation with the literal temporary path and URL:

curl -fsSL -o '{snapshot_tmp}/source.pdf' '{pdf_url}'

Then extract locally:

pdfinfo -isodates "$snapshot_tmp/source.pdf" > "$snapshot_tmp/pdfinfo.txt"
pdfinfo -meta "$snapshot_tmp/source.pdf" > "$snapshot_tmp/pdfmeta.xml" || true
pdftotext -enc UTF-8 -eol unix -nopgbrk \
  "$snapshot_tmp/source.pdf" "$snapshot_tmp/extracted.txt"

Use Read to inspect pdfinfo.txt, non-empty pdfmeta.xml, and a bounded beginning of extracted.txt. DOI metadata inspection is best effort and its failure does not make an otherwise successful capture fail. Treat PDF metadata fields as leads, not as authority: confirm the title and authors against the document text when available. Use Grep plus bounded Read ranges to locate an abstract, executive summary, introduction, or the source document's own DOI when the beginning does not supply enough metadata. Do not treat a DOI found only in the references as the paper's DOI. Do not read the whole extracted file merely to copy it. If extracted.txt is empty or contains no substantive text, go to Step 3.

Set capture_method to pdftotext, set body_file to {snapshot_tmp}/extracted.txt, and go to Step 4.

Step 2d: Fetch Web Page

Verify that the HTML capture prerequisites are available:

command -v curl
command -v trafilatura

If either command is missing, use another available fetch or extraction tool, or go to Step 3. Do not install prerequisites.

Create a temporary directory and retain the printed path as {snapshot_tmp}:

set -e
mkdir -p kb/reports/cache/snapshot-web
snapshot_tmp=$(mktemp -d kb/reports/cache/snapshot-web/capture.XXXXXX)
printf 'Snapshot temp: %s\n' "$snapshot_tmp"

Download with curl in a separate Bash invocation. Substitute the literal temporary path and source URL before running:

curl -fsSL -o '{snapshot_tmp}/source.html' -A 'Mozilla/5.0' '{source_url}'

If the download fails, go to Step 3. Otherwise extract from the saved HTML through standard input; do not use Trafilatura's -u download option or its -i URL-list option:

trafilatura \
  --markdown --with-metadata --links --no-comments --recall \
  < "{snapshot_tmp}/source.html" > "{snapshot_tmp}/extracted.md"

If extraction fails, go to Step 3.

Use Read to inspect only the leading metadata and a bounded beginning of extracted.md. Its leading YAML block, when present, is Trafilatura metadata: retain it as input to Step 4 but do not copy that block into the snapshot body. Use Grep with bounded output on {snapshot_tmp}/source.html to inspect article-level DOI metadata such as citation_doi, dc.identifier, prism.doi, or a JSON-LD doi property. DOI inspection is best effort: inability to inspect the raw HTML does not make an otherwise successful capture fail. Strip that block locally without re-emitting the document:

awk '
NR == 1 && $0 == "---" { in_metadata = 1; next }
in_metadata && $0 == "---" { in_metadata = 0; next }
!in_metadata { print }
' "{snapshot_tmp}/extracted.md" > "{snapshot_tmp}/body.md"

If body.md is empty, contains no substantive main content, or contains only an access-denied page or browser challenge instead of the article, go to Step 3.

Set capture_method to trafilatura, set body_file to {snapshot_tmp}/body.md, and go to Step 4.

Step 3: Adapt to Capture Failures

Before declaring capture blocked, inspect the failure and the material already retrieved. Choose a bounded alternative supported by that evidence. Do not repeat an unchanged failing method or search indefinitely for more tools.

• If an extractor returns boilerplate, an empty body, or the wrong page section,

inspect bounded portions of the saved HTML. The requested content may be in the DOM or embedded JSON even when the default extractor misses it.

• For a linked comment or other subdocument, verify its identifier and author

against the URL and page records. Extract that record's content, not the surrounding page or replies. Include its footnotes and relevant links.

• You may parse embedded data locally without executing page scripts. Write the

recovered body directly to a local file. Raw HTML embedded in Markdown is acceptable when it preserves content that conversion would lose.

• If fetching fails or a tool is unavailable, use another available route to

the same source when permitted. For an image-only PDF, use available OCR only if you can check its fidelity; otherwise report that text capture is blocked.

After recovery, set body_file to the local extraction and capture_method to an accurate name for the method actually used, then continue at Step 4. Keep the raw response until the snapshot has been assembled and verified.

Stop and report the blocker when no evidence-backed route remains, fidelity or source identity cannot be established, or another route requires installation, new access, or material cost outside the request. State what was tried and what is missing. If a missing standard tool would resolve it, name its installation: uv tool install "trafilatura>=2.2", Poppler (poppler-utils on Debian/Ubuntu, poppler through Homebrew, or oschwartz10612.Poppler through WinGet), or curl. Offer pasted text as a fallback rather than the first response to tool failure. Remove the unique temporary directory before returning.

Step 4: Determine Metadata

(Only for PDF and web page paths — GitHub and X scripts handle their own metadata.)

This workflow supplies types/snapshot.md as the type, a global type specified in snapshot.md. Open that spec and verify from its own frontmatter that it is a type spec before determining metadata. Stop if it is missing or invalid.

From the bounded excerpts, extractor metadata, and source_url, determine:

• title: The article/post title. Use the first H1 if present, otherwise derive from content.
• author: If identifiable from the content or URL (e.g. simonwillison.net → Simon Willison)
• doi: For a scholarly article or paper, try to identify the DOI from the

source_url, extractor or document metadata, and the document's own title or citation block. Store the bare identifier beginning with 10.; remove a leading https://doi.org/ or doi: label and surrounding whitespace. Accept a candidate only when the source identifies it as the DOI of the captured work. A DOI found only in references is not sufficient. If candidates conflict or none is attributable to the captured work, omit doi; never guess or manufacture one.

• genre: the source's genre per the snapshot type spec's vocabulary. This is a surface judgment of what kind of document the source is as evidence — ingestion may correct it later. Prefer a value from the type spec's list; a value outside it validates with a warning, so extend only for a genuinely new evidential kind, not a container.
• capture_scope: full-source, partial-source, abstract, or excerpt

under the snapshot type contract. Judge the retained body, not the success of the extraction command. In particular, label a publisher page that exposes only an abstract as abstract, even when that abstract is substantive.

• description: One sentence describing what makes this source worth retrieving. Not a summary — a retrieval filter (e.g. "Anthropic CEO's capability-timeline predictions — verifiable domains get confident timelines, unverifiable ones get hedged"). Focus on what distinguishes this source from others on the same topic.
• slug: Lowercase, hyphenated, max 63 chars. The paired ingest adds

.ingest to the validated stem, so the snapshot basename must reserve those seven characters within the 70-character authored-artifact limit. Derive it from the title; shorten it to identifying words rather than copying the full title. Check the length before writing. An overlong proposed slug is a naming choice to fix automatically, not a reason to stop or ask the user. Example: simon-willison-karpathy-claws. For a re-observation, append the capture date as -YYYYMMDD within the same 63-character limit, and stop if a file with that name already exists.

For academic papers: prefer the title and complete author list printed in the paper over pdfinfo or Trafilatura metadata.

Step 5: Materialize the Snapshot

The extracted body must move from body_file to the snapshot through local byte copying. Never place the whole source body in a Write or Edit call.

Use Write to create {snapshot_tmp}/header.md with this content and no source body. End the file with the blank line after Date:

---
source: {source_url}
description: {description}
captured: "{YYYY-MM-DD}"
capture: {capture_method}
capture_scope: {capture_scope}
genre: {genre}
doi: "{bare DOI; omit this line when no DOI was verified}"
type: types/snapshot.md
---
 
# {title}
 
Author: {author}
Source: {source_url}
DOI: {bare DOI; omit this line when no DOI was verified}
Date: {publication date if known}
 

For a recovered capture, use the locally extracted body and record the capture boundary in the snapshot body when it needs clarification. Do not copy embedded transport wrappers, unrelated records, or site boilerplate as source content.

Trafilatura has already produced the default web body as Markdown. A PDF body remains the complete plain text emitted by pdftotext; plain text is valid Markdown. Do not make model-mediated PDF cleanup a condition of capture. If the user explicitly requested cleanup, transform bounded chunks into a candidate body, never send the whole document through one Write, and retain the raw extracted.txt as fallback. Set body_file to the candidate only after every source chunk is present and in order; otherwise keep the raw body.

Assemble the snapshot without sending the extracted bytes through model output:

set -e
snapshot_path="kb/sources/.snapshots/{slug}.md"
cp "{snapshot_tmp}/header.md" "$snapshot_path"
cat "{body_file}" >> "$snapshot_path"
header_bytes=$(wc -c < "{snapshot_tmp}/header.md")
body_bytes=$(wc -c < "{body_file}")
snapshot_bytes=$(wc -c < "$snapshot_path")
test "$snapshot_bytes" -eq "$((header_bytes + body_bytes))"

Compute SHA-256 after the file is complete. Hash the exact .md bytes, including frontmatter, line endings, and the presence or absence of a final newline. Do not include a PDF, JSON, image, or other capture companion. Verify that the saved body matches body_file and that the retained content matches the requested source and declared scope. Report the path using the exact line Snapshot saved: kb/sources/.snapshots/{slug}.md, followed by its lowercase checksum and a one- or two-line preview. Disclose any missing content and any alternative capture method used.

Critical Constraints

Never:

• Fabricate or hallucinate content not on the page
• Add analysis or commentary — this is capture, not ingestion
• Re-emit a complete extracted body through Write or Edit
• Make model-mediated cleanup a prerequisite for saving a snapshot
• Save final snapshots outside kb/sources/.snapshots/ or temporary

download/extraction files outside kb/reports/cache/snapshot-web/

• Install software or bypass access controls — use available permitted means or report the blocker

Always:

• Copy every body_file byte in order, including on alternative capture paths
• Include the source URL in frontmatter
• Use today's date for captured
• Check for duplicates before fetching
• Keep the snapshot and every capture companion local and ignored
• Remove the unique temporary download/extraction directory after the snapshot

is written and hashed