Microsoft has now put "Skills" in three places: SharePoint sites, Copilot Cowork, and Copilot Studio. They share the same Markdown SKILL.md format. They are not the same product.
If you have written a SharePoint AI Skill, the question carrying the most anxiety today is whether you should redo your work in Cowork. The answer is no. The runtimes are different. The audiences are different. The work each one fits is different. But the Markdown file you have already written is more portable than it looks.
This is the practitioner comparison. What each one is, what they share, how to deploy one Skill across multiple surfaces with light editing, and which surface to write for first.
The short answer
Two surfaces, two jobs.
- SharePoint AI Skills run on a single SharePoint site. Anyone on the site with View permission can run them. Anyone with Edit permission can author them. The Skill acts on that site's content only.
- Cowork Skills run in Microsoft 365 Copilot for one user. They live in the user's OneDrive. They reach across the user's full M365 surface: Outlook, Teams, Word, Excel, OneDrive, calendar, and SharePoint search.
A Cowork Skill cannot do site-shared work. A SharePoint AI Skill cannot reach across your mailbox and calendar. Pick the surface that matches the work.
What Cowork Skills are
Cowork Skills are how Microsoft 365 Copilot's new execution agent (Cowork) gets the right behaviour for the right task. Cowork ships with 13 built-in skills covering the core M365 surface:
Word, Excel, PowerPoint, PDF, Email, Scheduling, Calendar Management, Meetings, Daily Briefing, Enterprise Search, Communications, Deep Research, and Adaptive Cards.
These load automatically as Cowork needs them. The user does not enable them. They are part of how Cowork works.
The interesting part is custom Cowork Skills. Each user can author up to 20 custom Skills, stored in their OneDrive at /Documents/Cowork/Skills/<skill-name>/SKILL.md. The file is plain Markdown. Cowork discovers custom Skills at the start of each conversation, no enable step required.
The custom Skill is the part Microsoft has made obviously open. Anyone with a Microsoft 365 Copilot licence and Frontier program access can write one this afternoon, drop it in a OneDrive folder, and have Cowork run it tomorrow.
What SharePoint AI Skills are
If you are already on this site you know what these are. The short version, because this comparison needs the contrast.
A SharePoint AI Skill is a Markdown file at /Agent Assets/Skills/<skill-name>/SKILL.md in a SharePoint site. It captures a repeatable multi-step workflow in natural language. Anyone with Edit permission on the site can author one. Anyone with View permission can run it. The Skill acts on the site's content: libraries, lists, pages.
The full picture lives in What are SharePoint AI Skills and the broader landscape (Skills vs SharePoint agents vs Copilot Studio vs Power Automate) is in SharePoint Skills vs Copilot agents. The next section is the part that has changed.
They are cousins, not twins
The Skills concept did not start at Microsoft. Anthropic introduced it in late 2025 as a structured Markdown file format that gives Claude a reusable, named, step-by-step instruction set for a specific kind of task. The format was open and well-designed. Microsoft adopted the same format, twice.
Cowork Skills use SKILL.md. SharePoint AI Skills use SKILL.md. The structure of the file (frontmatter, instructions, examples, references) is the same across both. That is not a coincidence and it is the strongest signal that Microsoft is treating Skills as a multi-surface concept rather than a single-surface feature.
The runtime is what differs. The SKILL.md file describes behaviour. The runtime decides what the behaviour can act on, who can run it, and where the output goes. Two SKILL.md files with identical structure can produce very different outcomes depending on which surface they run on.
That is the cousin, not twin, relationship. Same DNA. Different lives.
Head-to-head comparison
| Dimension | Cowork Skills | SharePoint AI Skills |
|---|---|---|
| Lives in | OneDrive (/Documents/Cowork/Skills/<name>/SKILL.md) | SharePoint site (/Agent Assets/Skills/<name>/SKILL.md) |
| Scope | The user's full Microsoft 365 environment | One SharePoint site's content |
| Built-in count | 13 (Word, Excel, PowerPoint, PDF, Email, Scheduling, Calendar Management, Meetings, Daily Briefing, Enterprise Search, Communications, Deep Research, Adaptive Cards) | None (custom only) |
| Custom limit | 20 per user | Site-level (no documented hard cap) |
| Author permission | The user themselves | Anyone with Edit on the site |
| Run permission | The user themselves | Anyone with View on the site |
| Acts on external systems | Limited (via Cowork plugins) | No |
| Reasoning model | Multi-model (Claude plus Microsoft) | Anthropic Claude |
| Mobile | Yes (iOS, Android, since May 2026) | No (desktop and web only) |
| Licence | Microsoft 365 Copilot | Microsoft 365 Copilot |
| Status | Public preview (Frontier program) | Public preview |
Two things stand out from this table.
First, the licence is the same. If your team has Microsoft 365 Copilot, you can use both surfaces today. There is no per-Skill cost and no separate SKU.
Second, the audience is different. SharePoint AI Skills are built into the team's environment. They are shared. Cowork Skills are personal. They live in the user's own OneDrive and run for that user only.
That difference shapes everything else about which surface to write for.
The "one Skill, three surfaces" pattern
This is the part most articles skip. The Markdown file format is the same across Cowork, AI in SharePoint, and Copilot Studio. A well-written SKILL.md can be deployed in two or three places with light editing.
Worked example. Take a "weekly stakeholder briefing" Skill. The user-facing intent is the same on every surface: pull the latest project updates, summarise the week, generate the briefing.
On Cowork, the Skill reads the user's recent emails on the topic, pulls in calendar context for who has been involved, drafts a Word document, and sends a Teams message to the project channel announcing the briefing is ready. Five steps, four runtime touches.
On AI in SharePoint, the same Skill (renamed and edited) reads the project site's documents and pages, pulls the most recent updates, and produces a SharePoint page or a list item with the briefing. The "send a Teams message" step gets dropped because AI in SharePoint does not handle Teams. The "read emails" step gets dropped because the Skill is bounded to the site.
On Copilot Studio, the same Skill (rewritten as an agent topic) gets the cross-system version. It can read the project site, the Dynamics CRM record, the Salesforce account, and the GitHub repo. It can also schedule a recurring run and post to multiple channels.
Same intent. Same authoring concept. Three different surface adaptations.
The pattern is real but it is an authoring convention plus per-target adaptation, not pure portability. The promise that "you write the Skill once" is half true. You write the Skill's intent once. The runtime steps differ enough that you adapt.
The practical workflow: build the Skill on the surface where the most users will run it, then port versions to the other surfaces if the same intent is useful there.
The fastest way to test this for yourself is to write one SKILL.md for the simplest version of a workflow you do every week. Drop it in /Documents/Cowork/Skills/<your-skill-name>/SKILL.md. Then copy it into a SharePoint site at /Agent Assets/Skills/<your-skill-name>/SKILL.md. Edit each version to match its runtime. You will see the divergence immediately and you will know which one suits the work.
Which Skill surface to write for first
The decision is about the work, not the platform.
Start with SharePoint AI Skills if:
- The work lives in one SharePoint site
- Multiple people on the team need to run it
- The workflow is structured around documents and lists
- You want anyone with View permission to run it without configuration
This is most teams' starting point. Document validation, metadata enrichment, library housekeeping, per-site review routines. Site-shared work is the natural home of SharePoint AI Skills.
Start with Cowork Skills if:
- The work spans multiple M365 apps (calendar, email, deep research, file generation)
- The user is the only one running it
- The output needs to coordinate with other people via meetings or messages
- You have Frontier program access
Personal productivity work, cross-app workflows, daily briefings. This is where Cowork Skills shine. The 20-custom-skill cap is generous for personal use and the runtime reach across M365 is unique.
Use Copilot Studio agents if:
- The work needs to reach external systems (Dynamics, Salesforce, ServiceNow, custom APIs)
- It needs to run on a schedule or trigger on an event
- You need an audit trail beyond what the per-surface Skills give you
This is the broader landscape the existing comparison piece covers. Copilot Studio is a project, not a Skill. Use it when the boundary of either Skill surface is the wrong shape.
What changed in May 2026
Three updates landed on 5 May 2026 and they all shape how Cowork Skills sit in the picture.
Mobile. Cowork is now on iOS and Android. Before May 2026 it lived only on the desktop and the web. Mobile changes who uses it and when. A user on the train, between meetings, or at a customer site can now ask Cowork to draft an email, schedule a meeting, or pull a quick brief. The Skills you write get triggered in more contexts.
Plugins. Cowork now ships native integrations with Power BI (via Fabric IQ), Dynamics 365 (sales, customer service, ERP), and third-party connectors for LSEG, Miro, monday.com, and S&P Global Energy. Custom plugins are also possible. This narrows the gap between Cowork and Copilot Studio for cross-system work, although Copilot Studio still has the broader connector library and the audit features.
Skills emphasis. The May 5 announcement leads with Skills as one of the three pillars (alongside integrations and devices). Microsoft is signalling that Skills are the primary unit of reusable workflow inside Cowork, not a side feature. That is consistent with the broader move across the platform: Skills in Cowork, Skills in AI in SharePoint, custom Skills supported and encouraged.
None of this changes where SharePoint AI Skills sit. The site-scoped Skill is still the right answer for site-scoped work. What it does change is the question of where to invest your custom Skill writing time.
The decision in one sentence
SharePoint AI Skills for site-shared work, Cowork Skills for personal cross-app work, Copilot Studio for cross-system or scheduled work. Build the Skill on the surface that matches the work. Port to other surfaces with light editing only when the same intent is useful elsewhere.