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1010
1111## Why use Skills
1212
13Skills are reusable, filesystem-based resources that give Claude domain-specific expertise: workflows, context, and best practices that turn a general-purpose agent into a specialist. Unlike prompts (conversation-level instructions for one-off tasks), Skills load on demand, so you don't have to repeat the same guidance across conversations.
13Skills are reusable, filesystem-based resources that give Claude domain-specific expertise: workflows, context, and best practices that turn a general-purpose agent into a specialist. Unlike prompts (conversation-level instructions for one-off tasks), Skills load on demand, so you don’t have to repeat the same guidance across conversations.
1414
1515**Key benefits:**
1616
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2828
2929**Pre-built Agent Skills** are available on claude.ai, the Claude API, [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws), and [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry). On Microsoft Foundry, Agent Skills require a [Hosted on Anthropic deployment](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry#additional-features-not-supported-when-hosted-on-azure). See [Available Skills](https://platform.claude.com/docs/en/agents-and-tools/agent-skills/overview#available-skills) for the complete list.
3030
31**Custom Skills** let you package domain expertise and organizational knowledge. They're available across Claude's products: create them in Claude Code, upload them through the Claude API, or add them in claude.ai settings. On [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws) and [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry), upload custom Skills through the Skills API.
31**Custom Skills** let you package domain expertise and organizational knowledge. They’re available across Claude’s products: create them in Claude Code, upload them through the Claude API, or add them in claude.ai settings. On [Claude Platform on AWS](https://platform.claude.com/docs/en/build-with-claude/claude-platform-on-aws) and [Microsoft Foundry](https://platform.claude.com/docs/en/build-with-claude/claude-in-microsoft-foundry), upload custom Skills through the Skills API.
3232
3333<Note>
3434 **Get started:**
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3939
4040## How Skills work
4141
42Skills use Claude's VM environment to provide capabilities beyond what's possible with prompts alone. Claude operates in a virtual machine with filesystem access, allowing Skills to exist as directories containing instructions, executable code, and reference materials, organized like an onboarding guide you'd create for a new team member.
42Skills use Claude’s VM environment to provide capabilities beyond what’s possible with prompts alone. Claude operates in a virtual machine with filesystem access, allowing Skills to exist as directories containing instructions, executable code, and reference materials, organized like an onboarding guide you’d create for a new team member.
4343
4444This filesystem-based architecture allows **progressive disclosure:** Claude loads information in stages as needed, rather than consuming context upfront.
4545
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4747
4848### Level 1: Metadata (always loaded)
4949
50The Skill's YAML frontmatter provides discovery information:
50The Skill’s YAML frontmatter provides discovery information:
5151
5252```yaml
5353---
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7979For advanced form filling, see [FORMS.md](FORMS.md).
8080````
8181
82When you request something that matches a Skill's description, Claude reads `SKILL.md` from the filesystem using bash. Only then does this content enter the context window.
82When you request something that matches a Skill’s description, Claude reads `SKILL.md` from the filesystem using bash. Only then does this content enter the context window.
8383
8484### Level 3: Resources and code (loaded as needed)
8585
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111111
112112### The Skills architecture
113113
114Skills run in a code execution environment where Claude has filesystem access, bash commands, and code execution capabilities. Skills exist as directories on a virtual machine, and Claude interacts with them using the same bash commands you'd use to navigate files on your computer.
114Skills run in a code execution environment where Claude has filesystem access, bash commands, and code execution capabilities. Skills exist as directories on a virtual machine, and Claude interacts with them using the same bash commands you’d use to navigate files on your computer.
115115
116116<Frame>
117117 
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123123
124124**What this architecture makes possible:**
125125
126* **On-demand file access:** Claude reads only the files each task needs. A Skill can include dozens of reference files, but if your task only needs the sales schema, that's the one file Claude loads. The rest stay on the filesystem and cost zero tokens.
127* **Efficient script execution:** When Claude runs `validate_form.py`, the script's code never loads into the context window. Only its output (such as "Validation passed" or a specific error message) consumes tokens, which makes scripts far more efficient than having Claude generate equivalent code during the task.
128* **No practical limit on bundled content:** Files don't consume context until accessed, so Skills can include comprehensive API documentation, large datasets, or extensive examples. There's no context penalty for bundled content that isn't used.
126* **On-demand file access:** Claude reads only the files each task needs. A Skill can include dozens of reference files, but if your task only needs the sales schema, that’s the one file Claude loads. The rest stay on the filesystem and cost zero tokens.
127* **Efficient script execution:** When Claude runs `validate_form.py`, the script’s code never loads into the context window. Only its output (such as “Validation passed” or a specific error message) consumes tokens, which makes scripts far more efficient than having Claude generate equivalent code during the task.
128* **No practical limit on bundled content:** Files don’t consume context until accessed, so Skills can include comprehensive API documentation, large datasets, or extensive examples. There’s no context penalty for bundled content that isn’t used.
129129
130130### Example: Loading a PDF processing Skill
131131
132Here's how Claude loads and uses the custom `pdf-processing` Skill from the earlier examples (not the pre-built `pdf` Skill):
132Here’s how Claude loads and uses the custom `pdf-processing` Skill from the earlier examples (not the pre-built `pdf` Skill):
133133
1341341. **Startup:** System prompt includes: `pdf-processing - Extract text and tables from PDF files, fill forms, merge documents. Use when working with PDF files or when the user mentions PDFs, forms, or document extraction.`
1352. **User request:** "Extract the text from this PDF and summarize it"
1352. **User request:** “Extract the text from this PDF and summarize it”
1361363. **Claude calls:** `bash: cat pdf-processing/SKILL.md` → Instructions loaded into context
1371374. **Claude determines:** Form filling is not needed, so `FORMS.md` is not read
1381385. **Claude executes:** Uses instructions from `SKILL.md` to complete the task
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143143
144144## Where Skills work
145145
146Skills are available across Claude's agent products:
146Skills are available across Claude’s agent products:
147147
148148<Note>
149149 Claude Platform on AWS and Microsoft Foundry inherit the same Skills behavior as the Claude API in all following sections, except where [Limitations and constraints](https://platform.claude.com/docs/en/agents-and-tools/agent-skills/overview#limitations-and-constraints) says otherwise.
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167167
168168**Custom Skills:** Create Skills as directories with `SKILL.md` files. Claude discovers and uses them automatically.
169169
170Custom Skills in Claude Code are filesystem-based and don't require API uploads: place them in `~/.claude/skills/` (personal) or `.claude/skills/` (project).
170Custom Skills in Claude Code are filesystem-based and don’t require API uploads: place them in `~/.claude/skills/` (personal) or `.claude/skills/` (project).
171171
172172To learn more, see [Use Skills in Claude Code](https://code.claude.com/docs/en/skills).
173173
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214214* Maximum 64 characters
215215* Must contain only lowercase letters, numbers, and hyphens
216216* Cannot contain XML tags
217* Cannot contain reserved words: "anthropic", "claude"
217* Cannot contain reserved words: `anthropic`, `claude`
218218
219219`description`:
220220
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226226
227227## Security considerations
228228
229Use Skills only from trusted sources: those you created yourself or obtained from Anthropic. Skills give Claude new capabilities through instructions and code, which also means a malicious Skill can direct Claude to call tools or run code in ways that don't match the Skill's stated purpose.
229Use Skills only from trusted sources: those you created yourself or obtained from Anthropic. Skills give Claude new capabilities through instructions and code, which also means a malicious Skill can direct Claude to call tools or run code in ways that don’t match the Skill’s stated purpose.
230230
231231<Warning>
232232 If you must use a Skill from an untrusted or unknown source, exercise extreme caution and thoroughly audit it before use. Depending on what access Claude has when running the Skill, malicious Skills could lead to data exfiltration, unauthorized system access, or other security risks.
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234234
235235**Key security considerations:**
236236
237* **Audit thoroughly:** Review all files bundled in the Skill: `SKILL.md`, scripts, images, and other resources. Look for unusual patterns such as unexpected network calls, file access patterns, or operations that don't match the Skill's stated purpose.
237* **Audit thoroughly:** Review all files bundled in the Skill: `SKILL.md`, scripts, images, and other resources. Look for unusual patterns such as unexpected network calls, file access patterns, or operations that don’t match the Skill’s stated purpose.
238238* **External sources are risky:** Skills that fetch data from external URLs pose particular risk, as fetched content might contain malicious instructions. Even trustworthy Skills can be compromised if their external dependencies change over time.
239239* **Tool misuse:** Malicious Skills can call tools (file operations, bash commands, code execution) in harmful ways.
240240* **Data exposure:** Skills with access to sensitive data could be designed to leak information to external systems.
241241* **Treat like installing software:** Be especially careful when integrating Skills into production systems with access to sensitive data or critical operations.
242242
243For organization-scale governance, vetting, and deployment guidance, see [Skills for enterprise](https://platform.claude.com/docs/en/agents-and-tools/agent-skills/enterprise). Claude Enterprise organizations can also turn on [Skill content scanning](https://platform.claude.com/docs/en/agents-and-tools/agent-skills/enterprise#skill-content-scanning) for custom Skills uploaded in claude.ai and Claude Cowork. Scanning doesn't cover Skills uploaded through the Skills API or the Claude Console.
243For organization-scale governance, vetting, and deployment guidance, see [Skills for enterprise](https://platform.claude.com/docs/en/agents-and-tools/agent-skills/enterprise). Claude Enterprise organizations can also turn on [Skill content scanning](https://platform.claude.com/docs/en/agents-and-tools/agent-skills/enterprise#skill-content-scanning) for custom Skills uploaded in claude.ai and Claude Cowork. Scanning doesn’t cover Skills uploaded through the Skills API or the Claude Console.
244244
245245## Available Skills
246246
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267267
268268## Data retention
269269
270Agent Skills is not covered by ZDR arrangements. Skill definitions and execution data are retained according to Anthropic's standard data retention policy.
270Agent Skills is not covered by ZDR arrangements. Skill definitions and execution data are retained according to Anthropic’s standard data retention policy.
271271
272272For ZDR eligibility across all features, see [API and data retention](https://platform.claude.com/docs/en/manage-claude/api-and-data-retention).
273273
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312312
313313* **Claude Code:**
314314
315 * **Full network access:** Skills have the same network access as any other program on the user's computer.
316 * **Global package installation discouraged:** Skills should only install packages locally to avoid interfering with the user's computer.
315 * **Full network access:** Skills have the same network access as any other program on the user’s computer.
316 * **Global package installation discouraged:** Skills should only install packages locally to avoid interfering with the user’s computer.
317317
318318Plan your Skills to work within these constraints.
319319
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325325 </Card>
326326
327327 <Card title="Using Agent Skills with the API" icon="code" href="https://platform.claude.com/docs/en/build-with-claude/skills-guide">
328 Learn how to use Agent Skills to extend Claude's capabilities through the API.
328 Learn how to use Agent Skills to extend Claude’s capabilities through the API.
329329 </Card>
330330
331331 <Card title="Use Skills in Claude Code" icon="terminal" href="https://code.claude.com/docs/en/skills">
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