moonming/a6-plugin-ai-prompt-template

a6-plugin-ai-prompt-template

Overview

The ai-prompt-template plugin pre-configures prompt templates with {{variable}} placeholders. Clients submit only the template name and variable values; the plugin fills the template and produces a complete chat-completion request. This enforces prompt structure and prevents clients from sending arbitrary system prompts.

Priority: 1071 (runs before ai-prompt-decorator at 1070 and ai-proxy at 1040).

When to Use

• Enforce a fixed prompt structure across all clients
• Accept user inputs only for specific fields (fill-in-the-blank)
• Prevent prompt injection by controlling the system message
• Build prompt libraries that clients select by name

Plugin Configuration Reference

| Field | Type | Required | Description | |-------|------|----------|-------------| | templates | array | Yes | Array of template objects (min 1) | | templates[].name | string | Yes | Template identifier (min length 1) | | templates[].template | object | Yes | Template specification | | templates[].template.model | string | Yes | AI model name | | templates[].template.messages | array | Yes | Array of message objects (min 1) | | templates[].template.messages[].role | string | Yes | system, user, or assistant | | templates[].template.messages[].content | string | Yes | Prompt content with {{variable}} placeholders |

Template Variable Syntax

Use double curly braces: {{variable_name}}

Variables are replaced by matching keys in the client request body. The plugin uses the body-transformer plugin internally for substitution.

Client Request Format

Instead of sending a standard messages array, clients send:

{
  "template_name": "my-template",
  "variable1": "value1",
  "variable2": "value2"
}

The plugin looks up the template by name, fills in the variables, and produces a complete chat-completion request body.

Step-by-Step: Create a Templated Route

1. Create a route with ai-prompt-template and ai-proxy

a6 route create -f - <<'EOF'
{
  "id": "templated-chat",
  "uri": "/v1/chat/completions",
  "methods": ["POST"],
  "plugins": {
    "ai-proxy": {
      "provider": "openai",
      "auth": {
        "header": {
          "Authorization": "Bearer sk-your-key"
        }
      },
      "options": {
        "model": "gpt-4"
      }
    },
    "ai-prompt-template": {
      "templates": [
        {
          "name": "code-review",
          "template": {
            "model": "gpt-4",
            "messages": [
              {
                "role": "system",
                "content": "You are an expert {{language}} code reviewer. Review the code for bugs, performance issues, and style."
              },
              {
                "role": "user",
                "content": "Review this code:\n\n{{code}}"
              }
            ]
          }
        }
      ]
    }
  }
}
EOF

2. Send a request with template variables

curl http://127.0.0.1:9080/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
    "template_name": "code-review",
    "language": "Python",
    "code": "def add(a, b): return a + b"
  }'

3. What the plugin sends to OpenAI

{
  "model": "gpt-4",
  "messages": [
    {
      "role": "system",
      "content": "You are an expert Python code reviewer. Review the code for bugs, performance issues, and style."
    },
    {
      "role": "user",
      "content": "Review this code:\n\ndef add(a, b): return a + b"
    }
  ]
}

Common Patterns

Multiple templates on one route

{
  "plugins": {
    "ai-prompt-template": {
      "templates": [
        {
          "name": "translate",
          "template": {
            "model": "gpt-4",
            "messages": [
              {
                "role": "system",
                "content": "Translate the following text from {{source_lang}} to {{target_lang}}. Return only the translation."
              },
              {
                "role": "user",
                "content": "{{text}}"
              }
            ]
          }
        },
        {
          "name": "summarize",
          "template": {
            "model": "gpt-4",
            "messages": [
              {
                "role": "system",
                "content": "Summarize the following text in {{style}} style, using at most {{max_sentences}} sentences."
              },
              {
                "role": "user",
                "content": "{{text}}"
              }
            ]
          }
        }
      ]
    }
  }
}

Clients select the template by name:

# Translation
curl http://127.0.0.1:9080/v1/chat/completions \
  -d '{"template_name":"translate","source_lang":"English","target_lang":"Chinese","text":"Hello world"}'

# Summarization
curl http://127.0.0.1:9080/v1/chat/completions \
  -d '{"template_name":"summarize","style":"concise","max_sentences":"3","text":"Long article..."}'

Combining with ai-prompt-decorator

The pipeline executes in priority order:

1. ai-prompt-template (1071) — fills variables
2. ai-prompt-decorator (1070) — prepends/appends messages
3. ai-proxy (1040) — sends to LLM

{
  "plugins": {
    "ai-prompt-template": {
      "templates": [
        {
          "name": "qa",
          "template": {
            "model": "gpt-4",
            "messages": [
              {"role": "user", "content": "{{question}}"}
            ]
          }
        }
      ]
    },
    "ai-prompt-decorator": {
      "prepend": [
        {"role": "system", "content": "Be concise and factual."}
      ],
      "append": [
        {"role": "system", "content": "Cite sources if possible."}
      ]
    },
    "ai-proxy": {
      "provider": "openai",
      "auth": {
        "header": {"Authorization": "Bearer sk-your-key"}
      }
    }
  }
}

Config Sync Example

version: "1"
routes:
  - id: templated-chat
    uri: /v1/chat/completions
    methods:
      - POST
    plugins:
      ai-proxy:
        provider: openai
        auth:
          header:
            Authorization: Bearer sk-your-key
        options:
          model: gpt-4
      ai-prompt-template:
        templates:
          - name: code-review
            template:
              model: gpt-4
              messages:
                - role: system
                  content: "You are an expert {{language}} code reviewer."
                - role: user
                  content: "Review this code:\n\n{{code}}"
          - name: explain
            template:
              model: gpt-4
              messages:
                - role: system
                  content: "Explain {{topic}} at a {{level}} level."
                - role: user
                  content: "{{question}}"

Troubleshooting

| Symptom | Cause | Fix | |---------|-------|-----| | 400 "template not found" | template_name doesn't match any configured template | Check spelling; names are case-sensitive | | Unfilled {{variable}} in output | Variable key missing from request body | Include all template variables in the request JSON | | Plugin not transforming | Wrong plugin name or misconfigured | Verify plugin name is ai-prompt-template (not prompt-template) | | Conflict with direct messages | Client sends both template_name and messages | Use only template_name + variables; the plugin replaces the entire body |