Lesson 17.517.5 When to write your own connector

In everyday life. For dinner, you can cook with what you have (a built-in tool), follow a recipe card (a skill), or order in (a connector). Ordering in is worth it when the food is out of your reach. To order in, you can pick from a restaurant's menu (a ready-made connector), or hire a cook who makes exactly your dishes (your own connector). Neither is worth it for a sandwich you can make yourself.

What you will learn. When a job needs a connector, and when writing your own is worth the upkeep.

Why it matters. A connector is a service someone must keep running, so writing one for a job a script could do wastes time and money.

Two jobs, start to finish. Ana has two jobs she wants an AI to help with:

• Policy search. AP clerks use a chat app, the builder uses a coding agent, and finance tries a different AI app. All three need cited answers from the same AP policies.
• The due-by-Friday list. One person runs it, in one project folder, with one coding agent. A tested script already does it.

The first job becomes a tool in a connector Brightline writes. The second stays a script inside a skill. Why the difference?

How do I decide where a job belongs?

Chapter 16 placed each job by asking questions in order, and stopping at the first yes. Must it never happen? A hook or a setting. Is it in another system? A connector. Must a number be exact? Your own tested code. Can the agent already do it? A built-in tool. Is it side work that would crowd the session? A helper agent. Otherwise, a skill.

This chapter widens the connector question and adds a second one.

First question: does the job need a connector at all?

Yes, when at least one of these is true:

• It is in another system the AI cannot reach on its own, such as an accounting system, a database, or files behind a login.
• Several AI apps need it. One connector serves every AI app that speaks MCP. A script serves one agent in one project.
• A rule must hold whichever app asks, such as fields that must never leave. The connector applies the rule for every app.

The due-by-Friday list meets none of these. It reads only the weekly invoice export, which holds no bank details, in the one project folder its one user works in. So a tested script can read the file directly, and no connector is needed to guard it. A skill says when to run the script. Policy search meets the second: three AI apps need the same answers.

Second question: a ready-made connector, or your own?

Look for a ready-made one first, and use it if it reaches your system and gives only the access you want. Write your own when:

• None knows your system or your work, such as Brightline's purchase orders and AP policies.
• The ready-made one gives too much, as Chapter 16's did: it could change files, and it handed over whole files.
• It cannot keep your rules, such as fields that must never leave, or a password for the business system that the model must never see.

What does a connector cost?

Every tool description is sent to the model each time it is asked anything. A connector is also a running service: it has a web address, an access key, a place it runs online, and someone who answers when it breaks. So when a tested script or a skill does the job, use that.

What does a connector control, and what does it not?

A connector controls what can be asked and what data comes back. It cannot tell whether a person really wants an action done right now. That decision belongs to the AI app's settings and, for anything that changes data or moves money, to a person who approves it (17.7, Chapter 23).

At work. Ana and the builder settle both jobs as above. Policy search needs a connector, because three AI apps need it. Chapter 16's ready-made connector could open the policy files, but only as whole files. It could not search them or cite a line. So policy search becomes the search_policy tool in Brightline's own connector. The due-by-Friday list stays a tested script in a skill, because a connector would add upkeep without a single new user.

The operating rule: use a connector when the job is in another system, when several AI apps need it, or when a rule must hold whichever app asks. Use a ready-made one if it fits. Write your own when no ready-made one fits: none knows your system, it gives too much, or it cannot keep your rules. Otherwise, use a skill or a tested script.

Figure 17.10. Inside the connector step there are two choices: use a ready-made connector if one fits, or write your own when none knows your system or keeps your rules.