Most agent failures we see are not bad answers. They are good answers to the wrong question, repeated four hundred times overnight.
That is why every agent block in Tessel ships with three limits that sit outside the prompt.
A spend cap
Each agent has a monthly budget in euros. The runtime counts tokens and tool calls against it and stops the agent, not the workflow, when it runs out. The run continues on the fallback path you defined.
A tool list
An agent can only call the tools you list, with the scopes you grant. Reading a Ledgerline invoice and posting a journal entry are different permissions, and most agents only need the first one.
A named approver
Anything that moves money, changes access or writes to a system of record waits for a person. The approver gets the agent's reasoning, the inputs and a one-tap decision in Chatline.
- Budgets reset on the first of the month.
- Tool scopes are versioned with the block.
- Every approval names a backup.
Prompts still matter. They just should not be the only thing standing between an agent and your ledger.
Written by the people who build Tessel. We publish notes on engineering, operations and product every few weeks.
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