Write Your First Method

This guide walks you through creating a working .mthds file from scratch. By the end, you will have a method that generates a short summary from a text input.

Prerequisites

• A text editor with MTHDS support. Install the VS Code extension for the best experience.
• The plxt CLI installed for formatting (see Formatting & Linting).
• The mthds CLI installed for validation.

Step 1: Create a .mthds File

Create a new file called summarizer.mthds and add a domain header:

domain      = "summarization"
description = "Text summarization methods"

Every bundle starts with a domain — a namespace for the concepts and pipes you will define. The domain name uses snake_case segments separated by dots.

Step 2: Define a Concept

Add a concept to describe the kind of data your method produces:

domain      = "summarization"
description = "Text summarization methods"

[concept]
Summary = "A concise summary of a longer text"

This declares a simple concept called Summary. It has no internal structure — it is a semantic label that gives meaning to the data your pipe produces.

Concept codes use PascalCase (e.g., Summary, ContractClause, CandidateProfile).

Step 3: Define a Pipe

Add a pipe that takes text input and produces a summary:

domain      = "summarization"
description = "Text summarization methods"
main_pipe   = "summarize"

[concept]
Summary = "A concise summary of a longer text"

[pipe.summarize]
type        = "PipeLLM"
description = "Summarize the input text in 2-3 sentences"
inputs      = { text = "Text" }
output      = "Summary"
prompt      = """
Summarize the following text in 2-3 concise sentences. Focus on the key points.

@text
"""

Here is what each field does:

• type = "PipeLLM" — this pipe uses a large language model to generate output.
• inputs = { text = "Text" } — the pipe accepts one input called text, of the native Text type.
• output = "Summary" — the pipe produces a Summary concept.
• prompt — the LLM prompt template. @text is shorthand for {{ text }}, injecting the input variable.

The main_pipe = "summarize" header marks this pipe as the bundle's primary entry point.

Step 4: Format Your File

Run the formatter to ensure consistent style:

plxt fmt summarizer.mthds

The formatter aligns entries, normalizes whitespace, and ensures your file follows MTHDS style conventions.

Step 5: Validate

Validate your bundle:

mthds validate summarizer.mthds

If everything is correct, you will see a success message. If there are errors — a misspelled concept reference, an unused input, a missing required field — the validator reports them with specific messages.

The Complete File

domain      = "summarization"
description = "Text summarization methods"
main_pipe   = "summarize"

[concept]
Summary = "A concise summary of a longer text"

[pipe.summarize]
type        = "PipeLLM"
description = "Summarize the input text in 2-3 sentences"
inputs      = { text = "Text" }
output      = "Summary"
prompt      = """
Summarize the following text in 2-3 concise sentences. Focus on the key points.

@text
"""

This file works as a standalone bundle — no manifest, no package, no dependencies. To run it:

mthds run summarizer.mthds

File Naming Conventions

When organizing .mthds files in a project:

• Use snake_case for file names: invoice_processing.mthds, cv_analysis.mthds.
• Match the file name to the bundle's domain when practical. A bundle with domain = "invoice_processing" lives naturally in invoice_processing.mthds.
• Use the .mthds extension — it is required by the toolchain for validation and formatting.

Next Steps

• Add more concepts and pipes to your bundle. See The Language for the full set of pipe types and concept features.
• When you are ready to distribute your methods, see Create a Package.