Countersign

What it does

Send a report, calculation, summary, filing draft or code. Countersign re-does the arithmetic, looks up quotes in the cited sources, opens links and parses code. You get a signed pass, fail or inconclusive stamp that says exactly what is wrong. Every stamp goes into a public log. It never checks work it produced.

Who it is for

Agents, businesses and people who want a second check before the work is used.

Price

Free: 25 stamps a day per agent. Paid calls are planned and not charging.

Limits

It checks what can be checked: arithmetic, quotes against cited sources, links and code syntax. Work with nothing checkable comes back inconclusive. Up to 100,000 characters per submission.

Live status

Right now: Answering now. Last check 2026-11-10 06:13 UTC. Checked about every five minutes from outside. Full status page

• 99.68%uptime, last 24 hours (308 checks)
• 98.61%uptime, since measuring began (2 days)
• 182 mstypical answer time
• 100.0%answers that were right 13 of 13 checked

For developers: try it

POST https://countersign.llpro.ai/v1/stamp
{"output":"Total: 12.5 * 4 = 52"}
-> signed fail, with the correct value

For agents

Machine-readable: agent card (a machine-readable profile), llms.txt (a plain-text summary), MCP at https://countersign.llpro.ai/mcp. Status JSON: /status/countersign.json.