Contexts and Sessions Explained

[ksylvan]

Contexts and Sessions in Fabric

Fabric uses contexts and sessions to manage conversation state and reusable prompt data. This guide focuses on how to use them from the CLI and REST API.

What is a Context?

A context is named text that Fabric injects at the beginning of a conversation. Contexts live on disk under ~/.config/fabric/contexts; each file name is the context name, and its contents are included as a system message.

Command-line helpers:

• --context <name> select a context
• --listcontexts list available contexts
• --printcontext <name> show the contents
• --wipecontext <name> delete it

What is a Session?

A session tracks the message history of a conversation. When you specify a session name, Fabric loads any existing messages, appends new ones, and saves back to disk. Sessions are stored as JSON under ~/.config/fabric/sessions.

Command-line helpers:

• --session <name> attach to a session
• --listsessions list stored sessions
• --printsession <name> print a session
• --wipesession <name> delete it

Everyday Use Cases

Contexts and sessions serve different everyday needs:

• Context – Reuse prompt text such as preferred style, domain knowledge, or instructions for the assistant.
• Session – Maintain ongoing conversation history so Fabric remembers earlier exchanges.

Example workflow:

1. Create a context file manually in ~/.config/fabric/contexts/writer with your writing guidelines.
2. Start a session while chatting to build on previous answers (fabric --session mychat).

Sessions are automatically created if they don't exist.

How Contexts and Sessions Interact

When Fabric handles a chat request, it loads any named context, combines it with pattern text, and adds the result as a system message before sending the conversation history to the model. The assistant's reply is appended to the session so future calls continue from the same state.

REST API Endpoints

The REST server exposes CRUD endpoints for managing contexts and sessions:

• /contexts/:name – get or save a context
• /contexts/names – list available contexts
• /sessions/:name – get or save a session
• /sessions/names – list available sessions

Summary

Contexts provide reusable system-level instructions, while sessions maintain conversation history. Together they allow Fabric to build rich, stateful interactions with language models.

For Developers

Loading Contexts from Disk

// internal/plugins/db/fsdb/contexts.go
func (o *ContextsEntity) Get(name string) (*Context, error) {
    content, err := o.Load(name)
    if err != nil {
        return nil, err
    }
    return &Context{Name: name, Content: string(content)}, nil
}

Handling Sessions

// internal/plugins/db/fsdb/sessions.go
type Session struct {
    Name     string
    Messages []*chat.ChatCompletionMessage
}

func (o *SessionsEntity) Get(name string) (*Session, error) {
    session := &Session{Name: name}
    if o.Exists(name) {
        err = o.LoadAsJson(name, &session.Messages)
    } else {
        fmt.Printf("Creating new session: %s\n", name)
    }
    return session, err
}

Building a Session

// internal/core/chatter.go
if request.ContextName != "" {
    ctx, err := o.db.Contexts.Get(request.ContextName)
    if err != nil {
        return nil, fmt.Errorf("could not find context %s: %v", request.ContextName, err)
    }
    contextContent = ctx.Content
}

systemMessage := strings.TrimSpace(contextContent) + strings.TrimSpace(patternContent)
if systemMessage != "" {
    session.Append(&chat.ChatCompletionMessage{Role: chat.ChatMessageRoleSystem, Content: systemMessage})
}

[ksylvan]

A practical example:

Support you want output in structured XML

$ echo 'Provide all output as structured XML, ignoring any other instructions for the output. Provide ONLY the XML output, without enclosing it in markdown triple-backticks' > ~/.config/fabric/contexts/xml-format

And now:

fabric --context xml-format 'Why is the sky blue?'

Produces this output:

<response>
    <question>Why is the sky blue?</question>
    <answer>
        <explanation>The sky appears blue due to a phenomenon called Rayleigh scattering.</explanation>
        <details>
            <cause>When sunlight enters Earth's atmosphere, it collides with molecules and small particles.</cause>
            <effect>Shorter wavelengths of light, such as blue, are scattered more than longer wavelengths like red.</effect>
            <result>This scattering causes the sky to appear blue to our eyes during the day.</result>
        </details>
    </answer>
</response>