Three different things are sold under the word automation. Robotic process automation (RPA) drives existing screens the way a person would, clicking and typing, useful when a system has no interface for software and no way to get one. Workflow automation moves data between systems on defined rules and triggers, through their interfaces, and is what most business processes need. An AI agent reads, decides and acts towards a goal, using a model for the judgement, and is needed only when the inputs are unstructured and the decisions cannot be written as rules. Three questions decide it: does the system have an interface for software; can the decision be written as a rule; and is the input structured. Most SME processes are a workflow with a model in one step, reading a document or drafting a message, at a fraction of the cost of an agent and with none of the agent’s controls to run.
- RPA
- Drives screens; last resort
- Workflow
- Rules between interfaces; the usual answer
- Agent
- Judgement on unstructured input; the exception
The three, defined by what decides
The simplest way to tell them apart is to ask what makes the decision at each step: a script, a rule you wrote, or a model.
| RPA | Workflow automation | AI agent | |
|---|---|---|---|
| What decides | A script following a screen | Rules you wrote | A model, within limits you set |
| How it reaches systems | Clicks and types on the screen | Interfaces and connectors | Interfaces, connectors, MCP |
| Input it handles | Structured, predictable screens | Structured data and events | Unstructured text, documents, conversations |
| Breaks when | The screen changes | The rule is wrong or the data is | The model misjudges or is injected |
| Controls needed | Monitoring of the script | Testing of the rules | Least privilege, ceilings, human confirmation, logging |
| Typical UK cost | Licence per bot plus build | Tool subscription or a build at £4,000 to £15,000 | Custom system at £8,000 to £25,000 |
Three questions that decide it
Does the system have an interface for software, an API, an import, a connector? If yes, never use RPA for it; use a workflow. If no and it cannot be given one, RPA is the last resort, with the understanding that it breaks when the screen changes. Can the decision be written as a rule, if this then that, with a finite list of cases? If yes, a workflow does it, deterministically and cheaply. If no, because the input is free text or the judgement is genuinely contextual, a model is needed for that step. Is the whole process a chain of such judgements with actions between them, or is there one judgement in an otherwise rule-based flow? One judgement means a workflow with a model in that step. A chain means an agent, and the controls that come with it.
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Why most processes are a workflow with a model in one step
Reading a supplier invoice into structured fields is a model step; everything after it, matching to the order, posting, filing, is rules. Classifying an incoming email is a model step; routing it is rules. Drafting a reply is a model step; sending after approval is rules. In each case the model does the one thing rules cannot and the workflow does everything else, which keeps the model cost to pence, the behaviour predictable, and the failure modes visible. An agent that decides the whole chain is right for a small number of processes: a receptionist conversation, an enquiry qualified across several turns, an investigation across systems. Buying an agent for a process that needed a workflow is how firms end up with an unpredictable system and a bill.
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When RPA is still right
When a system the firm depends on has no interface, will not get one, and cannot be replaced yet: a legacy practice system, a supplier portal, a government form. RPA keeps the process moving while the real fix is planned, and it should be treated as temporary and monitored, because the day the screen changes it stops. Increasingly, a model driving a browser does the same job with more tolerance for small screen changes, which is worth knowing when a vendor quotes for RPA.
What to ask a supplier
Which of the three is this, and why? Where exactly is a model making a decision, and what happens when it is wrong? What are the controls if it acts? What does it cost per unit to run, and what are the ceilings? And what breaks it? A supplier who calls everything an agent, or everything RPA, is selling what they have rather than what the process needs. The honest answer to most SME processes is a workflow with one model step, and it is the cheapest answer too.
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Common questions
What is the difference between RPA and AI agents?
RPA runs a fixed script against existing screens; an AI agent uses a model to read, decide and act towards a goal. RPA breaks when a screen changes; an agent can misjudge or be manipulated, so it needs least privilege, ceilings and human confirmation.
What is workflow automation?
Software that moves data between systems on rules and triggers, through their interfaces. It is what most business processes need, with a model added only for the step rules cannot do, such as reading a document or drafting a message.
When does a business need an AI agent?
When the process is a chain of judgements on unstructured input with actions between them: a receptionist conversation, multi-turn enquiry qualification, an investigation across systems. One judgement in a rule-based flow is a workflow with a model step, not an agent.
Is RPA obsolete?
Nearly. It remains the last resort for a system with no interface that cannot yet be replaced, treated as temporary. Models driving a browser now do the same job with more tolerance for change.
What does each cost for a UK SME?
RPA: a licence per bot plus build. Workflow: a tool subscription or a fixed-price build at £4,000 to £15,000. Agent: a custom system at £8,000 to £25,000 with a stated running cost and controls.
How do I know which one a vendor is selling me?
Ask where a model makes a decision, what happens when it is wrong, what the controls are if it acts, and what breaks it. The answers place it in one of the three.