Meeting canvases · Systems
Sequence diagrams, drawn live while your team talks through the flow
A sequence diagram shows one scenario as a conversation between participants: each participant is a vertical lifeline, each message is an arrow, and you read it from top to bottom in the order things happen. Teams draw one to agree how a flow such as a login, a payment or an API call really works, including what happens when a step fails or is slow.
Troopa draws it during your call on Teams, Zoom or Google Meet. Say “Hi Troopa, draw a sequence diagram of the card payment”, and each participant and message appears in order as people walk through the flow, with replies dashed and notes where someone adds one.
14 days free, no card. Then $15 per seat, per month. Cancel any time. Last checked against the product on 21 October 2026.
Why sequence diagrams are drawn badly, or not at all
- Drawing one by hand means placing every lifeline and arrow one at a time, so nobody does it until the night before the meeting.
- The diagram tries to show every path at once and becomes impossible to follow.
- It describes how someone remembers the flow, not how the people who own each part say it works.
- Half the room does not know what a dashed arrow means, so the picture explains nothing to them.
- It is drawn once for the design and is wrong a month later, so nobody trusts it.
- On a video call, one person drawing while the others describe the flow falls behind within a minute.
How to draw a sequence diagram on a call with Troopa
Step 1: Open the diagram
Say “Hi Troopa, draw a sequence diagram of the card payment”. When the room starts walking through who calls whom, Troopa may offer one.
Step 2: Walk through the flow
“The checkout creates a payment, then the API asks the fraud service to score it.” Each participant and numbered message appears in the order it is said.
Step 3: Add replies and notes
“The bank says approved” is drawn as a dashed reply; “that can take three seconds” becomes a note beside the bank’s lifeline.
Step 4: Put it in order
Drag a step up or down on the card, or say “the fraud check comes before the bank, not after”, and it is redrawn in the new order.
Step 5: Present and keep it
Present it to check every arrow with the people who own each participant, then download it as SVG, PNG, PDF, Markdown or CSV, with the messages in order.
A sequence diagram example: a card payment with a fraud check
A payments team walks through a new card payment flow on Google Meet before building it. Lena leads with Troopa open; Kofi owns the payments API.
- Lena“Hi Troopa, draw a sequence diagram of the card payment.”
- Kofi“The shopper presses pay, and the checkout creates a payment in our payments API.”
- Lena“The API asks the fraud check to score it, and it comes back low risk.”
- Kofi“Then we ask the bank to authorise the card. That can take up to three seconds.”
- Lena“The bank says approved, and we confirm the payment back to the checkout.”
- Kofi“So what happens if the bank hasn’t answered in three seconds?”
Sequence diagrams in different industries
Banking and fintech
A payment initiation and consent flow between the customer, the payment provider and the bank’s servers, the way open banking specifications themselves draw it, agreed with the partner bank’s team on the call.
Healthcare IT
An app launching from the records system and being authorised, or the messages between scheduling, records and billing when a patient is admitted. Integration flows only, never clinical decisions.
Telecoms and contact centres
Setting up a call between a phone, a proxy and a gateway: telecoms engineers have drawn call flows this way for decades, and the internet standards for calls are written as them.
E-commerce
Checkout across the basket, stock, the payment provider and the order service, and what the customer sees when the payment provider is slow.
SaaS and identity
Single sign-on and the steps of an OAuth login, or what happens across five systems when a new starter is given access, walked through with the identity team.
Agencies and consultancies
Agreeing an integration with a client’s developers: who calls whom, with what, and what comes back, so the contract between the systems is settled before anyone builds it.
A sequence diagram template, as a table
Here is how to draw a sequence diagram as a table first. One scenario per diagram: put the participants in order from the person who starts it, through the apps and services, to the data stores and outside systems, and number every message.
Scenario: [one flow, e.g. “card payment, approved”] Starts when: [the trigger] Participants, left to right: [person, app, services, stores, outside systems] # | From | To | Message | Kind | Notes 1 | [participant] | [participant] | [what is sent] | call | 2 | [participant] | [participant] | [what is sent] | call | [timeout, retry] 3 | [participant] | [participant] | [what comes back] | reply (dashed) | Other paths: [a short alternative here, or a separate diagram if it is long] Open questions: [what happens if a step is slow, fails or is repeated?]
Questions to ask at every arrow
- Who starts this flow, and what triggers it?
- Does the caller wait for an answer, or carry on?
- What happens if this call is slow, fails or is sent twice? Is it safe to repeat?
- Where does the state live after each step, and what does the user see meanwhile?
- Where does the flow cross from one organisation’s systems to another’s?
- Is any step done by a person, and how long can it take?
Questions about sequence diagrams
What is a sequence diagram used for?
To agree how one scenario works across several systems or people: who sends what to whom, in what order, and what comes back. It is especially useful for designing an API, an integration with another company, or a flow that has to cope with slow or failing steps.Microsoft, Azure Well-Architected Framework: design diagrams →
How do you draw a sequence diagram?
Pick one scenario, list the participants left to right in the order they first take part, and draw each as a box with a dashed line down from it. Then add the messages as numbered arrows from top to bottom in the order they happen, with replies as dashed arrows back.
What do the arrows in a sequence diagram mean?
In a UML® sequence diagram, a solid arrow with a filled head is a call the sender waits on, an open arrowhead is a message the sender does not wait for, and a dashed arrow is a reply. Many teams use simpler conventions, which is fine as long as everyone reading the diagram knows them.Object Management Group, What is UML →
How do you show if, else and loops in a sequence diagram?
UML draws them as labelled frames around the messages concerned: alt for alternatives, opt for an optional step, loop for repetition and par for steps in parallel. If the alternative is long, a separate diagram for that path is usually clearer than a frame.
What is the difference between a sequence diagram and a flowchart?
A flowchart shows the steps and decisions of one process; a sequence diagram shows the messages passed between several participants over time. Use a flowchart for what one actor does, and a sequence diagram for how several talk to each other.
What is the difference between a sequence diagram and an architecture diagram?
An architecture diagram shows the parts of a system and which ones talk to each other; a sequence diagram follows one scenario across those parts in time order. Reviews often move from the first to the second for the flow that matters most.
Sources
- Object Management Group, What is UML
- Microsoft, Azure Well-Architected Framework: design diagrams
- Scott Ambler, Agile Modeling: UML sequence diagrams
Read on 15 October 2026, by the people who make Troopa.
UML® and Unified Modeling Language™ are either registered trademarks or trademarks of Object Management Group, Inc. in the United States and/or other countries.
Try it in your next meeting
Install Troopa on your Mac, Windows PC or Ubuntu computer, join your call on Teams, Zoom or Google Meet as you always do, and ask: “Hi Troopa, draw a sequence diagram of the card payment.”
14 days free, no card. Then $15 per seat, per month. Cancel any time.