Understanding Skills
Skills are markdown files (SKILL.md) that teach your AI assistant domain knowledge about a set of tools — workflow patterns, data model concepts, and API gotchas that aren't captured in tool descriptions.
What is a Skill?
A SKILL.md file is a document that gives your AI assistant contextual expertise for a specific domain.
Tools tell your AI what it can do. Skills tell it how to do it well.
For example, PostHog has 40+ tools for analytics, experiments, and feature flags. The tool descriptions explain parameters, but they don't tell your AI that:
$pathnamegives cleaner results than$current_urlfor URL breakdowns- Experiment results come from a separate endpoint, not the experiment object
- Session recording snapshots require a two-step blob key fetch
- You should always test a query with
posthog_run_querybefore saving it as an insight
A SKILL.md file captures this kind of knowledge so your AI doesn't have to learn it through trial and error.
Skills vs Tool Descriptions
| Tool Descriptions | Skills | |
|---|---|---|
| Scope | Single tool | Entire domain / bundle |
| Content | Parameters, types, required fields | Workflows, gotchas, data model relationships |
| Updated | Automatically via MCP | Manually authored domain knowledge |
| Example | "event: string (required)" | "Always discover event definitions before writing queries" |
How Skills Work
Skills follow the open SKILL.md standard — a simple format with YAML frontmatter and markdown body:
---
name: posthog
description: Domain knowledge for PostHog product analytics tools
---
# PostHog
PostHog organizes everything under Organizations → Projects...
## Data Model
- **Events** are the atomic unit...
## Workflows
- **Ad-hoc analysis**: List event definitions → run query → save as insight...
## Gotchas
- **`$pathname` vs `$current_url`**: Use `$pathname` for cleaner breakdowns...
When your AI assistant loads the skill, it gains this knowledge before making any tool calls.
Skills + MCP Bundles
Skills and bundles are designed to work together:
- The bundle provides authenticated tool access — your AI can call PostHog APIs, create HubSpot contacts, or query your database
- The skill provides domain expertise — your AI knows the right patterns, avoids common mistakes, and follows optimal workflows
You can use skills without bundles (just domain knowledge), and bundles without skills (tools with trial-and-error learning). But together, your AI assistant becomes genuinely competent at the task.
Where Skills Live
Every MCPBundles bundle can have an associated skill. Skills are:
- Browsable at mcpbundles.com/skills
- Downloadable as SKILL.md files from any bundle or skill page
- Available via MCP — call the
get_skilltool on any bundle endpoint to retrieve the skill content programmatically
Composed Bundle Skills
When you create a custom server by composing multiple bundles (e.g., PostHog + HubSpot), the get_skill tool automatically merges skills from all constituent bundles into a single document. Your AI gets domain knowledge for every service in the composition.