Prompt
Instructions typed into one conversation. Great for one-off tasks, but they stay tied to that chat: no portable folder structure, no on-demand discovery, and no agreed way to bundle the resources a task needs.
An Agent Skill is a portable folder that packages specialist knowledge for an AI agent: a SKILL.md file with instructions, plus any scripts and reference material the task needs. The agent loads the Skill only when it is relevant, so one agent can carry many skills without bloating its context. Anthropic introduced Agent Skills on October 16, 2025, and released the format as an open standard on December 18, 2025, so Claude Code, Claude.ai, the Claude API, and a growing list of tools all understand the same folder. Portability still has limits: bundled scripts may need a specific runtime or network access, tool permissions differ between hosts, and host-specific extensions can require adaptation.
A Skill is a directory named after what it does. The only required file is SKILL.md:
--- name: pdf-form-filler description: Fill PDF forms accurately. Use when the user needs to complete or validate a PDF form. --- # PDF form filling 1. Inspect the form fields with scripts/inspect_fields.py 2. Map user data to field names 3. Fill and verify against references/field-rules.md
Skills use progressive disclosure. At startup the agent sees only the name and description of every installed Skill. It reads the full SKILL.md when the Skill looks relevant, and opens bundled files only when the task demands them. Specialist knowledge stays available without consuming context until it is needed.
The three solve different problems and work well together:
Instructions typed into one conversation. Great for one-off tasks, but they stay tied to that chat: no portable folder structure, no on-demand discovery, and no agreed way to bundle the resources a task needs.
A reusable package of instructions plus resources, versioned in git like code. Write the playbook once; every compatible agent can load it on demand.
The Model Context Protocol connects agents to live external systems: databases, APIs, internal tools. MCP answers "what can the agent reach"; a Skill answers "what does the agent know how to do".
Because the format is an open standard, one Skill travels between hosts:
Skills live in terminals and chat apps, which makes them hard to hand to a client, a teammate, or an audience that just wants answers. Converting a Skill into a web app gives it a public URL: a focused chat page grounded in the Skill's own material, usable in any browser with nothing to install.
Turn your SKILL.md into a web appSkill2Web is an independent product and is not affiliated with Anthropic.