# How to Test Claude Skills Across Claude.ai, Claude Code, and the API

> Learn to test Claude Skills efficiently across Claude.ai, Claude Code, and the API. Master environment-specific workflows with a single source of truth.

- Repository: [Composio/awesome-claude-skills](https://github.com/composiohq/awesome-claude-skills)
- Tags: how-to-guide
- Published: 2026-07-26

---

**Claude Skills are self-contained instruction packages (a [`SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/SKILL.md) file plus optional scripts and assets) that can be validated across Claude.ai, Claude Code, and the Claude API using environment-specific testing workflows while maintaining a single source of truth.**

The ComposioHQ/awesome-claude-skills repository hosts standardized skill definitions that follow the open Anthropic Skills specification. Because the format is supported by all three platforms, you can verify functionality manually in the web interface, execute automated tests locally with Claude Code, and run programmatic validation through the API using identical folder structures and [`SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/SKILL.md) content.

## Understanding the Claude Skill Architecture

### The SKILL.md Format

A Claude Skill consists of a [`SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/SKILL.md) file containing instructions, optional scripts in a `scripts/` directory, and supporting assets. According to the repository's [`README.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/README.md), this format is an open standard supported by Anthropic, enabling portable skill definitions that function identically across platforms.

### Lazy Loading and Performance

The architecture implements lazy loading to optimize token usage. As documented in the [`README.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/README.md), only the skill's name and description are loaded initially; the full [`SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/SKILL.md) body (typically under 5,000 tokens) loads only when Claude determines the skill is relevant to the conversation.

### Bundled Resources and Scripts

Skills can include executable scripts that Claude invokes on demand. For example, the [`webapp-testing/SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/webapp-testing/SKILL.md) demonstrates Python Playwright scripts stored in the `scripts/` folder that Claude Code can execute directly during testing workflows.

## Platform-Specific Testing Workflows

### Testing on Claude.ai

Manual validation in the Claude.ai web interface involves uploading the skill folder or copy-pasting the [`SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/SKILL.md) content into the UI. Invoke the skill with simple prompts to verify LLM responses, then use Claude.ai's built-in "share" feature to test multi-step conversations. Iterate by fixing logic in [`SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/SKILL.md) and re-uploading.

### Testing with Claude Code

Claude Code enables local execution of skill scripts and automated testing suites. Navigate to the skill directory and open it with `claude-code .` to load the skill context. Execute bundled test scripts directly from the terminal—such as the Playwright-based tests in the webapp-testing skill—or run pytest to validate skill behavior before deployment.

### Testing via the Claude API

Programmatic validation uses the Claude SDK or direct API calls. Pass the skill definition in the `tools` payload of API requests, or point an API client at the local skill folder. Use the evaluation harness in [`mcp-builder/scripts/evaluation.py`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/mcp-builder/scripts/evaluation.py) to run automated test suites against a live MCP server, specifying the model (defaulting to `claude-3-7-sonnet-20250219`).

## Automated Testing Implementation

### Unit-Style Validation with Claude Code

For rapid iteration, invoke skills through the Claude SDK to assert JSON outputs. The [`connect-apps/SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/connect-apps/SKILL.md) (lines 97-115) demonstrates importing `ClaudeSDKClient` and `ClaudeAgentOptions` to programmatically run skills:

```python
from claude_agent_sdk.client import ClaudeSDKClient
from claude_agent_sdk.types import ClaudeAgentOptions

options = ClaudeAgentOptions(
    skill_dir="path/to/your/skill",
    model="claude-3-7-sonnet-20250219",
)

async with ClaudeSDKClient(options) as client:
    response = await client.run(
        prompt="Summarize the key steps for creating a PDF report."
    )
    print(response)

```

### Web UI Testing with Playwright

The webapp-testing skill provides ready-made Playwright scripts for validating UI-driven workflows. Execute tests using the bundled server wrapper as described in [`webapp-testing/SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/webapp-testing/SKILL.md) (lines 8-14):

```bash

# From the skill directory

python scripts/with_server.py --server "npm start" --port 3000 -- python test.py

```

### Running the Evaluation Harness

For comprehensive API validation, use the MCP builder evaluation script located at [`mcp-builder/scripts/evaluation.py`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/mcp-builder/scripts/evaluation.py):

```bash
python mcp-builder/scripts/evaluation.py \
    --model claude-3-7-sonnet-20250219 \
    --skill-dir path/to/skill \
    --questions tests/questions.json

```

The script defaults to `claude-3-7-sonnet-20250219` as specified in line 324 of the source file.

### Direct API Testing with cURL

Test skills without SDK dependencies using direct HTTP requests:

```bash
curl https://api.anthropic.com/v1/complete \
  -H "x-api-key: $ANTHROPIC_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
        "model": "claude-3-7-sonnet-20250219",
        "prompt": "Use the skill \"pdf-analyzer\" to extract tables from report.pdf.",
        "max_tokens_to_sample": 1024,
        "temperature": 0,
        "tools": [{"type":"skill","path":"./pdf-analyzer"}]
      }'

```

## Key Files for Skill Testing

Reference these repository files when implementing your testing strategy:

- **[`README.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/README.md)** – Overview of platform support and lazy loading architecture (line 433)
- **[`skill-creator/SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/skill-creator/SKILL.md)** – Authoring guidelines including metadata standards and testing best practices
- **[`skill-creator/scripts/init_skill.py`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/skill-creator/scripts/init_skill.py)** – Scaffolding script for generating new skill folders with proper [`SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/SKILL.md) templates
- **[`webapp-testing/SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/webapp-testing/SKILL.md)** – Documentation of the Playwright testing toolkit for UI validation (lines 2-3)
- **[`connect-apps/SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/connect-apps/SKILL.md)** – Examples of Claude SDK integration for programmatic skill execution
- **[`mcp-builder/scripts/evaluation.py`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/mcp-builder/scripts/evaluation.py)** – Command-line evaluation harness for automated API testing

## Summary

- Claude Skills use a standardized [`SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/SKILL.md) format that works across Claude.ai, Claude Code, and the Claude API without modification
- **Lazy loading** minimizes token usage by loading only the skill name/description until relevance is determined
- **Claude.ai** supports manual testing through UI uploads and conversation sharing
- **Claude Code** enables local script execution, including Playwright-based UI tests and pytest validation
- **Claude API** testing uses the evaluation harness ([`mcp-builder/scripts/evaluation.py`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/mcp-builder/scripts/evaluation.py)) or direct SDK/HTTP calls with the `tools` parameter
- The **webapp-testing** skill provides production-ready Playwright scripts for browser automation testing

## Frequently Asked Questions

### Can I use the same Claude Skill folder across all three platforms without modification?

Yes. According to the [`README.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/README.md) in ComposioHQ/awesome-claude-skills, the skill format follows the open Anthropic Skills standard, ensuring cross-platform compatibility. The same [`SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/SKILL.md) file and accompanying scripts work identically on Claude.ai, Claude Code, and the Claude API.

### What is the default model used when testing skills via the evaluation harness?

The evaluation script ([`mcp-builder/scripts/evaluation.py`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/mcp-builder/scripts/evaluation.py)) defaults to `claude-3-7-sonnet-20250219` when running automated tests. You can override this by passing the `--model` flag with your preferred Claude model identifier.

### How does lazy loading affect skill testing performance?

Lazy loading optimizes token consumption by loading only the skill's name and description initially. The full [`SKILL.md`](https://github.com/ComposioHQ/awesome-claude-skills/blob/main/SKILL.md) content (typically under 5,000 tokens) loads only when Claude determines the skill is relevant to the current conversation, making testing more efficient across all platforms.

### What testing tools are available for validating web application interactions?

The `webapp-testing` skill in the repository provides Playwright-based testing scripts. These scripts, located in the `scripts/` folder, can be executed via Claude Code using commands like `python scripts/with_server.py` to automate browser interactions and validate UI workflows.