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systemprompt-templates

Template registry, loading, and rendering for systemprompt.io config-as-code AI governance deployments. Handlebars-powered template engine for the MCP governance pipeline with plugin architecture, priority resolution, and filesystem discovery.

Layer: Domain — business-logic modules that implement systemprompt.io features. Part of the systemprompt-core workspace.

Overview

Integrations · Extensible Architecture

This crate provides the core template system for discovering, loading, and rendering HTML templates using Handlebars. It supports a plugin architecture with providers, loaders, extenders, and component renderers.

Usage

[dependencies]
systemprompt-templates = "0.9.2"

use std::sync::Arc;
use systemprompt_templates::{
    CoreTemplateProvider, FileSystemLoader, TemplateRegistryBuilder,
};

async fn setup_templates() -> Result<(), Box<dyn std::error::Error>> {
    let provider = CoreTemplateProvider::discover_from("./templates").await?;
    let loader = FileSystemLoader::new(vec!["./templates".into()]);

    let registry = TemplateRegistryBuilder::new()
        .with_provider(Arc::new(provider))
        .with_loader(Arc::new(loader))
        .build_and_init()
        .await?;

    let html = registry.render("page", &serde_json::json!({
        "title": "Hello"
    }))?;

    Ok(())
}

File Structure

src/
├── lib.rs                  # Public exports and re-exports from template-provider
├── builder.rs              # TemplateRegistryBuilder for fluent construction
├── core_provider.rs        # CoreTemplateProvider for filesystem template discovery
├── embedded_defaults.rs    # EmbeddedDefaultsProvider bundling the in-tree defaults/
├── error.rs                # TemplateError and TemplateResult
└── registry/
    ├── mod.rs              # TemplateRegistry struct and Handlebars wiring
    ├── lifecycle.rs        # Initialization, partial registration, template loading
    ├── queries.rs          # render, has_template, and component lookup
    └── stats.rs            # RegistryStats reporter

defaults/
└── templates/              # Embedded HTML templates shipped with the crate

Modules

builder

Provides TemplateRegistryBuilder for fluent construction of TemplateRegistry instances. Supports chaining with_provider(), with_loader(), with_extender(), with_component(), and with_page_provider() methods.

core_provider

Implements CoreTemplateProvider which discovers HTML templates from a filesystem directory. Reads optional templates.yaml manifests for metadata and infers content types from template name suffixes (-post, -list).

embedded_defaults

EmbeddedDefaultsProvider exposes the in-tree defaults/templates/ bundle so consumers get a working engine without filesystem access.

error

Defines TemplateError with variants for common failure modes (NotFound, LoadError, CompileError, RenderError, NoLoader, NotInitialized) plus the TemplateResult alias.

registry

Core TemplateRegistry that coordinates providers, loaders, extenders, and component renderers. Uses Handlebars for compilation and rendering, registers a json helper for JSON-LD safe serialisation, and resolves template conflicts by priority (lower values win). Split into lifecycle, queries, and stats submodules.

Priority System

Templates are resolved by priority where lower values take precedence:

License

BSL-1.1 (Business Source License). Source-available for evaluation, testing, and non-production use. Production use requires a commercial license. Each version converts to Apache 2.0 four years after publication. See LICENSE.

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