> ## Documentation Index > Fetch the complete documentation index at: https://docs-test.symmetry.com/llms.txt > Use this file to discover all available pages before exploring further. # Ways to Use the STE > The five interfaces available for accessing the Symmetry Tax Engine. There are five ways to interact with the Symmetry Tax Engine, each suited to a different job. This page helps everyone on your team — engineers, analysts, support, and product — find the right tool for what they're trying to do. All five interfaces run against the same production STE — same tax tables, same calculation logic, same results. The difference is *how* you reach it and *what your team needs from it*. ## What do you need to do? | I need to… | Reach for... | | ------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------- | | Build or run payroll calculations in a production system | [**STE API / On-Premise SDK**](/ste/overview/hosted-vs-on-premise) | | Ask the STE a question in plain English (no code) | [**STE MCP**](/ste/ai-interfaces/ste-mcp) | | Understand why a specific paycheck calculated the way it did | [**STL Chat**](/ste/ai-interfaces/tax-logic-chat) | | Show employees a plain-English breakdown of their withholding | [**STL API**](/ste/ai-interfaces/tax-logic-api) | | Write integration code with STE-aware IDE suggestions | [**STE Copilot**](/ste/ai-interfaces/ste-developer-ai-copilot) or [**STL Copilot**](/ste/ai-interfaces/tax-logic-api/stl-api-developer-integration-kit) | ## Interfaces ### STE API / On-Premise SDK: production calculations The STE API is the core tax calculation engine. It accepts payroll inputs and returns precise federal, state, and local withholding results. Your engineers use it to power calculations inside your payroll platform. * **Best for:** engineers building or maintaining a payroll integration, and any automated workflow that needs structured output. * **Not designed for:** interactive questions, human-readable explanations, or exploration by non-developers. The engine is available two ways — as a hosted web API or as a locally installed SDK. See [Hosted API vs. On-Premise SDK](/ste/overview/hosted-vs-on-premise) to choose between them, then follow the [Hosted API Quickstart](/ste/quickstarts/hosted-api-quickstart) or an SDK quickstart ([Java](/ste/quickstarts/java-sdk-quickstart), [.NET](/ste/quickstarts/dotnet-sdk-quickstart), [C](/ste/quickstarts/c-sdk-quickstart)) to get started. ### STE MCP: ask the STE questions in plain English The STE MCP connects the tax engine to AI assistants your team already uses — Claude, Cursor, Copilot, and any other tool that supports the Model Context Protocol. Instead of assembling a JSON payload, you describe what you want, and the MCP returns a real, traceable STE result. * **Best for:** tax and compliance teams verifying jurisdiction rules or rate changes, support teams reproducing a client's calculation to diagnose a discrepancy, implementation teams validating address-to-jurisdiction mappings, and anyone who needs a real answer from the STE without writing code. * **Not designed for:** production pipelines or high-volume batch calculations. The MCP is built for interactive, human-driven use. * **Learn more:** [STE MCP](/ste/ai-interfaces/ste-mcp) **Example prompts:** * For pay date 2026-05-15, what taxes apply to a Pittsburgh, Allegheny County address? I need the Local Services Tax and EIT rate. * A client reports that Ohio SUTA 2025 isn't capping at \$9,000. Here's the calculation detail — run it through the STE and walk me through where the cap should have applied. * Run a \$3,000 regular wage in PA, NY, and CA — semi-monthly pay, single filing status, 1 exemption. Show me federal, state, and local totals side by side. ### STL Chat: understand why a paycheck calculated that way Symmetry Tax Logic (STL) Chat is a browser-based interface for walking through a specific paycheck result in plain English. Where the STE MCP suits open-ended exploration and hypotheticals, STL Chat is focused on taking a real calculation, interrogating it conversationally, and confirming it's correct. * **Best for:** support teams fielding "why did my check look like this?" questions, engineers reviewing an STE log file while implementing a new tax, and anyone verifying a real calculation without writing code or reading JSON. * **Not designed for:** hypothetical modeling or broad compliance research — use the STE MCP for those. * **Learn more:** [STL Chat](/ste/ai-interfaces/tax-logic-chat) ### STL API: explain withholding to your employees The STL API accepts paycheck context and returns a plain-English explanation you can surface directly in your product — inside a pay stub detail view, an HR portal, or a self-service paycheck screen. Employees get a clear answer to "why was this amount withheld?" without contacting support. * **Best for:** product and engineering teams building employee-facing paycheck experiences and reducing inbound support volume around withholding questions. * **Not designed for:** internal analyst workflows — use STL Chat instead. * **Learn more:** [STL API](/ste/ai-interfaces/tax-logic-api) ### STE Copilot and STL Copilot: smarter integration code The Copilots are context files that load Symmetry's documentation directly into your AI coding assistant (Cursor, Claude Code, or any compatible IDE). With the STE or STL Copilot active, your editor's AI suggestions are grounded in the actual STE and STL schema — correct parameter names, valid values, and real integration patterns. * **Best for:** engineers actively writing STE or STL integration code who want accurate, API-aware autocomplete without switching to documentation. * **Learn more:** [STE Developer AI Copilot](/ste/ai-interfaces/ste-developer-ai-copilot) · [STL API Developer Integration Kit](/ste/ai-interfaces/tax-logic-api/stl-api-developer-integration-kit) ## Side-by-side reference | | STE API / On-Premise SDK | STE MCP | STL Chat | STL API | Copilots | | ------------------ | ------------------------ | ----------------------------------- | ------------------------------- | ------------------- | ------------------------- | | **What it does** | Runs calculations | Answers questions | Explains a result | Embeds explanations | Improves code suggestions | | **How you use it** | REST API calls | AI chat interface | Browser UI | REST API calls | IDE / code editor | | **Who it's for** | Engineers | Analysts, support, PMs, payroll ops | Support, payroll ops, engineers | Engineers | Engineers | | **Requires code** | Yes | No | No | Yes | In-editor only | | **Coverage** | US and Canada | US and Canada | US only | US only | US and Canada | ## A note on data and trust The STE MCP, STL Chat, and STL API are all read-only. They cannot modify your payroll runs, employee records, or tax configuration — they are lenses on the engine, not controls for it. When Symmetry updates tax tables or rates, all five interfaces reflect those changes at the same time. There is no secondary data source to keep in sync.