Sync Blocker Auditor

Purpose

SharePoint accepts file and folder names that the OneDrive sync client, File Explorer, and the Teams Files tab later refuse to handle. The result is the classic "we can't sync this file" error that surfaces one user at a time, long after the content was uploaded, with no way to see how widespread the problem is.

This skill audits a document library against Microsoft's documented naming and path restrictions, scores its sync readiness, and produces a severity-ranked HTML report with a proposed safe name for every blocked item.

It is strictly read-only: it never renames, moves, deletes, checks in, or modifies any item. The only thing it writes is the HTML report file.

Trigger Phrases

Activate this skill when the user says any of the following (or close variations):

• "sync blockers" / "sync health check" / "sync readiness report"
• "why won't this library sync" / "OneDrive sync errors" / "sync is failing"
• "check file names" / "invalid file names" / "illegal characters" / "bad characters"
• "path too long" / "url too long" / "400 character limit"
• "files stuck checked out" / "who has files checked out"

Do not use this skill to actually rename or fix items. If the user asks for the fix to be applied, explain that this skill is read-only, hand them the rename plan from the report, and point them at a rename-capable skill or a bulk-rename tool.

Inputs & Scope

Determine the audit scope from the user's request and the current context, in this order:

1. Selected items or folder — if the user has items selected or says "these/this folder", audit that subtree.
2. Named library — if the user names one (e.g., "audit the Project Files library"), resolve it on the current site.
3. Current library — if the user is in a library and gives no other scope, audit it recursively from its root.
4. If no scope can be resolved, ask the user which library to audit. Do not guess.

Only audit content the current user can already see. Never invent items, paths, or values.

Steps

Step 1 — Resolve the library and enumerate every item

1. Resolve the target library and capture its server-relative root URL (needed for accurate path-length maths).
2. Use list_items with recursive=true to enumerate files and folders, projecting at minimum: FileLeafRef (name), FileRef (server-relative path), FileDirRef (parent path), FSObjType (0 = file, 1 = folder), File_x0020_Size, Modified, Editor, and the check-out fields (CheckoutUser / IsCheckedoutToLocal) when available.
3. Page through the entire library — do not stop at the first page. A single recursive list_items call can exceed the response-size limit above roughly 1,000 items, which is exactly the size of the migrated libraries this skill targets. If that happens, fall back to walking one folder at a time and aggregating the running totals with execute_code. If a read fails or returns partial data, record that plainly in the report's Limitations section instead of guessing.

Tell the user the scope and item count before analysing.

Step 2 — Apply the rule set

Do not evaluate the rules by eye. Use execute_code to do the character counting, pattern matching, and aggregation — exact URL lengths, character-class matches, and per-rule totals must be computed, not estimated.

An item can match several rules; record all matches, and rank the item by its highest severity. The Scope column says which item types a rule applies to.

Blockers (severity: Blocker — sync fails, or the item is unreachable from Explorer)

Risks (severity: Risk — works in the browser, breaks desktop clients, tooling, or migrations)

Info (severity: Info — noise that should not be in a synced library)

I1–I3 are advisory — never present them as sync failures. Never apply a files only rule to a folder: folders report a size of 0 and would otherwise all be flagged by I3.

Do not flag names merely for being vague, generic, or unhelpful (Document.docx, Untitled.xlsx, Misc), and do not flag leading-dot names such as .gitignore for having an empty base name. Readability is a different problem, handled by other skills. This skill only reports technical sync and URL blockers.

Step 3 — Propose a safe name for every Blocker

For each item with a Blocker, derive a suggested name — as a proposal only, never applied:

1. Replace every illegal character (B1) with a single -.
2. Replace #, %, &, {, }, + with - only when the item already has a Blocker; otherwise leave them and report as R1.
3. Collapse runs of - or spaces into one, then trim leading/trailing spaces, tabs, and periods.
4. For B4 reserved device names, prefix the name with file- (CON.docx → file-CON.docx). For B5/B6, first strip the reserved ~$ or _vti_ prefix, then add file- (~$Proposal.docx → file-Proposal.docx) — never leave the reserved prefix in place.
5. For B7/B8, shorten the base name — keep the first meaningful words, drop filler, and always preserve the original extension. State the new full-URL length.
6. If the proposal collides with an existing name in the same folder, append (2), (3), …
7. If a name cannot be made safe by renaming alone (for example, the path is long because of folder depth, not the file name), say so and recommend the folder-level fix instead.

Show both the original and the proposal so a human can approve each one.

Step 4 — Compute the scores

• Sync readiness % = items with no Blocker ÷ total items scanned, as a whole number.
• Counts of Blocker / Risk / Info items (an item counts once, at its highest severity).
• Rule frequency — how many items matched each rule ID, sorted descending.
• Folder hot spots — the folders containing the most affected items.
• Longest URL — the single worst path, with its character count.

Step 5 — Build a self-contained HTML report

Draft one self-contained HTML file:

• No scripts. No external CSS, fonts, images, or resources. Inline CSS only.
• Summary band — items scanned, sync readiness %, Blocker / Risk / Info counts, longest URL length, and the single most common rule.
• Severity strip — three coloured cards: Blocker (red #b3261e), Risk (amber #a16207), Info (blue #1e40af).
• Rule frequency chart — one row per matched rule showing rule ID, plain-English label, and a horizontal bar drawn with inline-CSS width (e.g., a coloured <div> at width: 62%), coloured by the rule's severity.
• Findings table — one row per affected item: name, folder path, severity badge, matched rule IDs, a plain-English reason, and the proposed safe name. Sort Blockers first.
• Path-length table — the 10 longest URLs with their character counts, each drawn as a bar against the 400-character SharePoint limit, with the 260-character Windows limit marked so it is obvious which items already break the desktop clients.
• Checked-out table — file, who has it checked out, and for how many days (omit the section entirely if there are none).
• Folder hot spots — the folders with the most affected items.
• Remediation list — a short, prioritised, plain-English list, most impactful first ("Rename 12 files containing : — sync fails for every user", "Flatten Projects/2026/Q3/... — 6 files are within 40 characters of the URL limit").
• Limitations section — only if any data was unavailable or the scan was partial.

Keep percentages as whole numbers and be consistent throughout the report.

Step 6 — Save the report

• Save the HTML file in a Sync Reports folder in the site's default Documents library (or Site Assets). Never write into the library under audit unless the user explicitly asks — writing a report into the audited scope changes the very thing that was just measured, and the reports accumulate as findings on the next run.
• Create the Sync Reports folder only if it does not exist, and only to hold the report.
• Use a clear filename: Sync-Blocker-Audit-<Library>-YYYY-MM-DD-HHMM.html.
• If the save fails because the user lacks write access anywhere on the site, do not stop — say the report could not be saved, and return the full findings inline as Markdown instead.

Step 7 — Respond to the user

After saving, reply with a compact Markdown summary and the report link:

# Sync blocker audit complete

[Open the report](<link>)

- Scope: <library / folder audited>
- Items scanned: <n> (<n> files, <n> folders)
- Sync readiness: <n>%  (Blockers <n> · Risks <n> · Info <n>)
- Top blocker: <rule label> on <n> items
- Longest URL: <n> characters (limit 400)

Example

User: "Why won't the Project Files library sync?"

Agent response after processing:

I audited Project Files (412 items — 366 files, 46 folders) against the OneDrive sync and URL rules.

Metric	Result
Sync readiness	91%
Blockers / Risks / Info	36 / 58 / 9
Top blocker	Illegal characters (B1) on 21 items
Longest URL	438 characters (limit 400)

The worst offender is Clients/Northwind/Contracts/Q3: Signed & Approved/ — the : in that folder name blocks every one of the 14 files inside it for every synced user.

I saved the report to Sync Reports/Sync-Blocker-Audit-Project-Files-2026-08-20-1130.html, including a proposed safe name for all 36 blocked items. Nothing was renamed.

Constraints

• Strictly read-only. Never rename, move, delete, check in, check out, or modify any item, folder, column, view, or setting. The only thing this skill writes is the HTML report file (and, if needed, the Sync Reports folder to hold it).
• Never fabricate items, paths, names, or check-out owners — everything comes from the actual library.
• Rename suggestions are proposals only. Always present them for human approval and state explicitly that nothing was changed.
• Measure URL length against the full decoded URL, not the file name alone, and always state the limit next to the number — 400 characters for SharePoint (B7), 260 for Windows (R2).
• Compute lengths, character matches, and totals with execute_code. Never estimate a character count by inspection.
• Report technical blockers only. Do not flag names for being vague, generic, or unhelpful.
• Page through the entire library; report partial results plainly if a tool fails.
• The HTML report must be fully self-contained: no scripts, no external resources, inline CSS only.
• Match on names case-insensitively, but always display the original name exactly as stored, including the whitespace that caused the finding (wrap such names in ` so trailing spaces stay visible).

References

• Restrictions and limitations in OneDrive and SharePoint — the disallowed names (.lock, desktop.ini, ~$…, _vti_, root forms) and the TMP-files behaviour behind B5, B6, and R6.
• What are the file path length limits? — the 400-character decoded-path limit (B7), the 255-character per-name limit (B8), and the 260-character Windows limit (R2).
• SharePoint Online limits

The illegal-character, whitespace, and trailing-period rules (B1–B3) are enforced by SharePoint and Windows at upload and rename time rather than being listed in the article above. They matter because content that arrived through migrations, the API, or third-party tools bypassed that enforcement — which is why these names exist in real libraries at all.