Prompt template syntax
The Semantic Kernel prompt template language is a simple way to define and compose AI functions using plain text. You can use it to create natural language prompts, generate responses, extract information, invoke other prompts or perform any other task that can be expressed with text.
The language supports three basic features that allow you to 1) include variables, 2) call external functions, and 3) pass parameters to functions.
You don't need to write any code or import any external libraries, just use the
curly braces {{...}} to embed expressions in your prompts.
Semantic Kernel will parse your template and execute the logic behind it.
This way, you can easily integrate AI into your apps with minimal effort and
maximum flexibility.
Tip
If you need more capabilities, we also support the Handlebars template engine, which allows you to use loops, conditionals, and other advanced features. See how to use the Handlebars template engine here.
Variables
To include a variable value in your prompt, use the {{$variableName}} syntax.
For example, if you have a variable called name that holds the user's name,
you can write:
Hello {{$name}}, welcome to Semantic Kernel!
This will produce a greeting with the user's name.
Spaces are ignored, so if you find it more readable, you can also write:
Hello {{ $name }}, welcome to Semantic Kernel!
Function calls
To call an external function and embed the result in your prompt, use the
{{namespace.functionName}} syntax.
For example, if you have a function called weather.getForecast that returns
the weather forecast for a given location, you can write:
The weather today is {{weather.getForecast}}.
This will produce a sentence with the weather forecast for the default location
stored in the input variable.
The input variable is set automatically by the kernel when invoking a function.
For instance, the code above is equivalent to:
The weather today is {{weather.getForecast $input}}.
Function parameters
To call an external function and pass a parameter to it, use the
{{namespace.functionName $varName}} and
{{namespace.functionName "value"}} syntax.
For example, if you want to pass a different input to the weather forecast
function, you can write:
The weather today in {{$city}} is {{weather.getForecast $city}}.
The weather today in Schio is {{weather.getForecast "Schio"}}.
This will produce two sentences with the weather forecast for two different
locations, using the city stored in the city variable and the "Schio"
location value hardcoded in the prompt template.
Notes about special chars
Semantic function templates are text files, so there is no need to escape special chars like new lines and tabs. However, there are two cases that require a special syntax:
- Including double curly braces in the prompt templates
- Passing to functions hardcoded values that include quotes
Prompts needing double curly braces
Double curly braces have a special use case, they are used to inject variables, values, and functions into templates.
If you need to include the {{ and }} sequences in your prompts, which
could trigger special rendering logic, the best solution is to use string values
enclosed in quotes, like {{ "{{" }} and {{ "}}" }}
For example:
{{ "{{" }} and {{ "}}" }} are special SK sequences.
will render to:
{{ and }} are special SK sequences.
Values that include quotes, and escaping
Values can be enclosed using single quotes and double quotes.
To avoid the need for special syntax, when working with a value that contains single quotes, we recommend wrapping the value with double quotes. Similarly, when using a value that contains double quotes, wrap the value with single quotes.
For example:
...text... {{ functionName "one 'quoted' word" }} ...text...
...text... {{ functionName 'one "quoted" word' }} ...text...
For those cases where the value contains both single and double quotes, you will
need escaping, using the special «\» symbol.
When using double quotes around a value, use «\"» to include a double quote
symbol inside the value:
... {{ "quotes' \"escaping\" example" }} ...
and similarly, when using single quotes, use «\'» to include a single quote
inside the value:
... {{ 'quotes\' "escaping" example' }} ...
Both are rendered to:
... quotes' "escaping" example ...
Note that for consistency, the sequences «\'» and «\"» do always render
to «'» and «"», even when escaping might not be required.
For instance:
... {{ 'no need to \"escape" ' }} ...
is equivalent to:
... {{ 'no need to "escape" ' }} ...
and both render to:
... no need to "escape" ...
In case you may need to render a backslash in front of a quote, since «\»
is a special char, you will need to escape it too, and use the special sequences
«\\\'» and «\\\"».
For example:
{{ 'two special chars \\\' here' }}
is rendered to:
two special chars \' here
Similarly to single and double quotes, the symbol «\» doesn't always need
to be escaped. However, for consistency, it can be escaped even when not required.
For instance:
... {{ 'c:\\documents\\ai' }} ...
is equivalent to:
... {{ 'c:\documents\ai' }} ...
and both are rendered to:
... c:\documents\ai ...
Lastly, backslashes have a special meaning only when used in front of
«'», «"» and «\».
In all other cases, the backslash character has no impact and is rendered as is. For example:
{{ "nothing special about these sequences: \0 \n \t \r \foo" }}
is rendered to:
nothing special about these sequences: \0 \n \t \r \foo