> ## Documentation Index
> Fetch the complete documentation index at: https://docs.crewai.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Agent Capabilities

> Understand the five ways to extend CrewAI agents: Tools, MCPs, Apps, Skills, and Knowledge.

## Overview

CrewAI agents can be extended with **five distinct capability types**, each serving a different purpose. Understanding when to use each one — and how they work together — is key to building effective agents.

<CardGroup cols={2}>
  <Card title="Tools" icon="wrench" href="/en/concepts/tools" color="#3B82F6">
    **Callable functions** — give agents the ability to take action. Web searches, file operations, API calls, code execution.
  </Card>

  <Card title="MCP Servers" icon="plug" href="/en/mcp/overview" color="#8B5CF6">
    **Remote tool servers** — connect agents to external tool servers via the Model Context Protocol. Same effect as tools, but hosted externally.
  </Card>

  <Card title="Apps" icon="grid-2" color="#EC4899">
    **Platform integrations** — connect agents to SaaS apps (Gmail, Slack, Jira, Salesforce) via CrewAI's platform. Runs locally with a platform integration token.
  </Card>

  <Card title="Skills" icon="bolt" href="/en/concepts/skills" color="#F59E0B">
    **Domain expertise** — inject instructions, guidelines, and reference material into agent prompts. Skills tell agents *how to think*.
  </Card>

  <Card title="Knowledge" icon="book" href="/en/concepts/knowledge" color="#10B981">
    **Retrieved facts** — provide agents with data from documents, files, and URLs via semantic search (RAG). Knowledge gives agents *what to know*.
  </Card>
</CardGroup>

***

## The Key Distinction

The most important thing to understand: **these capabilities fall into two categories**.

### Action Capabilities (Tools, MCPs, Apps)

These give agents the ability to **do things** — call APIs, read files, search the web, send emails. At execution time, all three resolve into the same internal format (`BaseTool` instances) and appear in a unified tool list the agent can call.

```python theme={null}
from crewai import Agent
from crewai_tools import SerperDevTool, FileReadTool

agent = Agent(
    role="Researcher",
    goal="Find and compile market data",
    backstory="Expert market analyst",
    tools=[SerperDevTool(), FileReadTool()],  # Local tools
    mcps=["https://mcp.example.com/sse"],     # Remote MCP server tools
    apps=["gmail", "google_sheets"],           # Platform integrations
)
```

### Context Capabilities (Skills, Knowledge)

These modify the agent's **prompt** — injecting expertise, instructions, or retrieved data before the agent starts reasoning. They don't give agents new actions; they shape how agents think and what information they have access to.

```python theme={null}
from crewai import Agent

agent = Agent(
    role="Security Auditor",
    goal="Audit cloud infrastructure for vulnerabilities",
    backstory="Expert in cloud security with 10 years of experience",
    skills=["./skills/security-audit"],        # Domain instructions
    knowledge_sources=[pdf_source, url_source], # Retrieved facts
)
```

***

## When to Use What

| You need...                                          | Use                | Example                                |
| :--------------------------------------------------- | :----------------- | :------------------------------------- |
| Agent to search the web                              | **Tools**          | `tools=[SerperDevTool()]`              |
| Agent to call a remote API via MCP                   | **MCPs**           | `mcps=["https://api.example.com/sse"]` |
| Agent to send emails via Gmail                       | **Apps**           | `apps=["gmail"]`                       |
| Agent to follow specific procedures                  | **Skills**         | `skills=["./skills/code-review"]`      |
| Agent to reference company docs                      | **Knowledge**      | `knowledge_sources=[pdf_source]`       |
| Agent to search the web AND follow review guidelines | **Tools + Skills** | Use both together                      |

***

## Combining Capabilities

In practice, agents often use **multiple capability types together**. Here's a realistic example:

```python theme={null}
from crewai import Agent
from crewai_tools import SerperDevTool, FileReadTool, CodeInterpreterTool

# A fully-equipped research agent
researcher = Agent(
    role="Senior Research Analyst",
    goal="Produce comprehensive market analysis reports",
    backstory="Expert analyst with deep industry knowledge",

    # ACTION: What the agent can DO
    tools=[
        SerperDevTool(),         # Search the web
        FileReadTool(),          # Read local files
        CodeInterpreterTool(),   # Run Python code for analysis
    ],
    mcps=["https://data-api.example.com/sse"],  # Access remote data API
    apps=["google_sheets"],                      # Write to Google Sheets

    # CONTEXT: What the agent KNOWS
    skills=["./skills/research-methodology"],    # How to conduct research
    knowledge_sources=[company_docs],            # Company-specific data
)
```

***

## Comparison Table

| Feature                 |    Tools   |     MCPs    |        Apps        |     Skills    |        Knowledge       |
| :---------------------- | :--------: | :---------: | :----------------: | :-----------: | :--------------------: |
| **Gives agent actions** |      ✅     |      ✅      |          ✅         |       ❌       |            ❌           |
| **Modifies prompt**     |      ❌     |      ❌      |          ❌         |       ✅       |            ✅           |
| **Requires code**       |     Yes    | Config only |     Config only    | Markdown only |       Config only      |
| **Runs locally**        |     Yes    |   Depends   | Yes (with env var) |      N/A      |           Yes          |
| **Needs API keys**      |  Per tool  |  Per server |  Integration token |       No      |      Embedder only     |
| **Set on Agent**        | `tools=[]` |  `mcps=[]`  |      `apps=[]`     |  `skills=[]`  | `knowledge_sources=[]` |
| **Set on Crew**         |      ❌     |      ❌      |          ❌         |  `skills=[]`  | `knowledge_sources=[]` |

***

## Deep Dives

Ready to learn more about each capability type?

<CardGroup cols={2}>
  <Card title="Tools" icon="wrench" href="/en/concepts/tools">
    Create custom tools, use the 75+ OSS catalog, configure caching and async execution.
  </Card>

  <Card title="MCP Integration" icon="plug" href="/en/mcp/overview">
    Connect to MCP servers via stdio, SSE, or HTTP. Filter tools, configure auth.
  </Card>

  <Card title="Skills" icon="bolt" href="/en/concepts/skills">
    Build skill packages with SKILL.md, inject domain expertise, use progressive disclosure.
  </Card>

  <Card title="Knowledge" icon="book" href="/en/concepts/knowledge">
    Add knowledge from PDFs, CSVs, URLs, and more. Configure embedders and retrieval.
  </Card>
</CardGroup>