Critical path

The critical path is the longest chain of dependent tasks in your plan. Every other task has slack; a critical task does not. If a critical task slips by an hour, the plan slips by an hour.

Where you find it

Two surfaces:

• On the canvas: critical edges are drawn in purple (kept distinct from the red used for failure sentinels), near-critical edges in amber. Every other edge is the default grey.
• The Critical Path tab: the full ordered list of critical tasks with their estimates, their probability of being on the critical path (some tasks are critical in almost every monte-carlo draw, others only in 30% of them), and their cumulative durations from project start.

The slack column

Every task in the Critical Path tab has a slack column: how much it can slip before it joins the critical path. A task with 30 minutes of slack will become critical the moment you spend 31 extra minutes on it. The Critical Path tab is sorted by slack ascending so the most-at-risk near-critical tasks sit immediately below the genuinely critical ones.

Why it’s probabilistic

Topolog doesn’t just compute the critical path from your point estimates. It uses each task’s duration distribution (the cv on every task) to compute two things:

• A point-estimate critical path: the chain when every task takes its expected duration.
• A list of near-critical tasks: tasks with a meaningful chance of becoming the bottleneck under uncertainty.

In a plan with three parallel paths of roughly equal length, the “critical” path can shuffle between them as tasks come in over or under estimate. Near-critical tasks are the ones you watch even though they aren’t formally on today’s critical chain.

What to do with it

Three patterns:

• Schedule critical work first. The day-view ranks critical tasks above near-critical above the rest, so your morning starts on the chain that determines your deadline.
• Pre-emptively decompose near-critical tasks. A 4-hour near-critical task hides risk. Decompose it and either the chain shortens, or you find a hidden dependency that wasn’t on the original graph.
• Watch for shifts. The critical path moves when you mark tasks done. A non-critical task running 2 hours over might pull its branch onto the critical path; Topolog will quietly redraw the purple edges so you can see where the new bottleneck is.

Related

• The scheduler - how the critical-path output feeds the day/week/month views.
• Spectrum - what the shape of your duration distribution tells you about deadline risk.