How does an agent find out what changed since its last run?

Short answer: Keep a watermark: the time your agent last checked. Each run, ask for changes since slightly before that time, read only the data types and files that changed, then move the watermark forward. With Fulcra, data-updates reports which data types and files changed and how many records, so the agent can skip everything else. Fulcra's agents page calls this the Feed-Driven Reactive Loop.

The problem

An agent that re-reads all its context every run is slow and expensive; one that reads nothing misses what other agents, devices or people added. It needs a cheap "what's new?" check before deciding what to load.

When this is a good fit

• The agent runs on a loop or schedule and its inputs live in Fulcra: files other agents write, custom records, or synced sources such as Apple Health, location and calendar.
• Several agents write to the same datastore and each needs to catch up on the others.

When it isn't

• Your inputs aren't in Fulcra. data-updates only covers data in your Fulcra datastore (and, with --include-shared, data others share with you), not your inbox, repo or other APIs.
• You need line-level diffs or to know who made a change. data-updates reports which types and files changed and record counts, not the changes themselves or their author.
• You need to react within seconds. There is no push; counts can lag a few minutes.

Other options

• Change events from the source system, such as webhooks or a message queue (Redis, n8n, Zapier).
• Your own cursor or checkpoint against each API you read.
• git for files in a repo, where git diff gives exact changes.

1. Add this loop to the agent's instructions. Use one watermark file per agent; watcher below is an example name.

   ## Each run
   1. Note the current UTC time in ISO 8601 as NOW, e.g. 2026-10-15T14:00:00Z.
   2. Read the last watermark:
      `uvx fulcra-api file download /agents/watcher/watermark.txt -`
      (first run: use "1 day" instead of a start/end pair below).
   3. Set START to 10 minutes before the watermark and ask what changed:
      `uvx fulcra-api data-updates START NOW`
      Add `--include-shared` to include data others share with you.
   4. Read only what changed:
      - data types: `uvx fulcra-api get-records <DataType from step 3> START NOW`
      - files: `uvx fulcra-api file download <path from step 3> -`
   5. Skip items you already handled (the 10-minute overlap repeats some).
   6. Save NOW as the new watermark:
      `uvx fulcra-api file upload watermark.txt /agents/watcher/watermark.txt`

   Record NOW before checking, not after, so nothing that lands during the run is missed. The overlap covers counts that lag a few minutes. Both data-updates and get-records accept two ISO 8601 times or one relative interval such as "3h" or "2 days".
2. MCP clients use get_data_updates, get_records and read_file.

FAQ

• Does it tell me what changed inside a file? No, only that the file changed. Keep your own copy from the last run if you need to compare.
• Is it free? There's a free tier with 5 GB and no credit card.
• Who can see my data? Only agents you authorize, plus anyone you explicitly share with (read-only). Data is encrypted at rest and in transit and never sold.

Related

• Cron agent and interactive agent sharing state
• Shared blackboard for agents
• Coordinating two Claude Code instances
• Async messaging between agents
• Agent guide: https://www.fulcradynamics.com/llms.txt

Written by Fulcra. We make one of the tools recommended on this page.