varia

Two tools for running AI agents

Varia is the agent system we use for day-to-day work: research, code, mail, travel. On a typical day it runs around two hundred agent tasks and several thousand model calls. To keep track of it we built two tools, Paragon and Session Debugger. We plan to release both as open source.

Paragon

Cost accounting for agent runs.

Paragon assigns every model call to the run, phase and agent that made it. For each day it shows where the spend went, what a typical run costs, and how much more a run costs when its prompt cache starts cold.

cost per run: median, p90, max
startup, execution and wrap-up shown separately
cold and warm cache starts compared
model, reasoning effort and service tier on every row
tool usage per turn, grouped by family

Paragon: one day of spend split by category on the left; per-run statistics, cold and warm starts and tool families on the right — One day of our own usage, shown as shares. Dollar totals are blurred.

Session Debugger

Read an agent session turn by turn, and ask it about any turn.

The debugger lays a session out as a timeline: each turn, each tool call with its full input and output, and the tree of sub-agents it started, with their cost. From any turn you can ask the agent a question. A read-only fork of the session answers from what the agent had seen up to that point. The original session is not modified.

every tool call in order on one ribbon; click to jump to it
full input and output of each call
delegation tree with per-agent cost
questions anchored to a specific turn

Session Debugger: one session's tool-usage table, the panel for asking the agent questions, and the tool-call ribbon — A real session: 54 turns, 80 tool calls, 38 child sessions.

Status

Both tools are in daily use on our own setup. We are separating them from the rest of Varia so they work with other agent stacks. The code will be published on GitHub. Session Debugger was first shown at a harness-building workshop at Kolektyw3 in Warsaw in September 2026.

Questions: Tomasz Kolinko, tomasz.kolinko@varia.dev