Pysince

Your agent already read the file. since tells it when the file changed.

CI Tests PyPI

Coding agents act on files they read minutes ago. Those files change: a formatter runs, a teammate pushes, another agent edits, a git pull lands. The agent never sees it, and acts on the stale version with full confidence. since tells it, on every tool call, exactly what changed.

pip install pysince

Zero dependencies. Works in Claude Code, Cursor, Copilot, and Antigravity. Any MCP client.

The problem is real, named, and everywhere

Agents read a file, reason about it for many steps, then act on it but the file changed underneath them, and nothing tells them. It has a name: the stale world model problem. On long-horizon coding tasks, frontier model success drops from around 70% to roughly 23%, and about 36% of those failures trace to context drift, not reasoning quality. The canonical shape: an agent reads a file at step 3, reasons about it through step 30, and writes it back at step 31, but another process edited it at step 17. The agent silently overwrites the newer version, and the task looks like it succeeded.

This shows up across every major agent tool:

• OpenAI Codex will overwrite any changes it didn't create: edit files while it works and it restores them, "every time."
• GitHub Copilot agents overwrite their own edits because "the editor's state is different from what the AI has in its session-based memory."
• Claude Code subagents read stale file versions, and its file cache diverges from disk with Read/Grep returning the stale copy - the reporter concludes only an out-of-band disk check catches it.
• Continue has the same class of bug.
• With parallel agents, this compounds into silent file overwrites and stale views of the codebase, where agents "proceed silently on corrupted data rather than surfacing exceptions."

It's a recognized production blocker - 32% of agent teams cite output consistency as their #1 issue and there are whole guides written just on stopping agents from overwriting your work.

since is the lightweight, single-install out-of-band check: it fingerprints every file the agent reads and, on every tool call, reports which ones changed on disk before the agent acts.

What it does

Every MCP tool response surfaces all files that changed since the agent last read them. The agent does not have to remember to check. since volunteers it:

Files changed since last read:
  config.json (content changed, mtime changed) - read 4m ago
  alerts.py   (content changed, mtime changed) - read 3m ago

The agent re-reads those files before acting, instead of writing from a stale copy.

When you need this

Strongest when files change outside the agent's view: another process, a teammate on the same repo, a formatter, a pre-commit hook, a parallel agent, or context that drifted over a long session.

Less useful for quick single-file edits an agent already re-reads on its own. Skip it for throwaway scripts. Reach for it when agents share files, sessions run long, or more than one actor touches the tree.

Setup

since runs as a local MCP server. Add it to your client's MCP config.

VS Code:

{
  "servers": {
    "pysince": {
      "type": "stdio",
      "command": "pysince-mcp",
      "args": [],
      "cwd": "${workspaceFolder}"
    }
  }
}

Antigravity:

{
  "mcpServers": {
    "pysince": {
      "command": "python",
      "args": ["-m", "since.mcp"]
    }
  }
}

Then add this line to your agent's system instructions so it knows when to call the tools:

On the first read of any file, call stamp_file_read. Before editing a file, call check_staleness. When the response lists changed files, re-read them before acting on their contents.

Tools

Tool	When to call it	What it does
stamp_file_read	After reading any file	Records mtime and content hash
check_staleness	Before editing a file	Reports if it changed, and lists every other tracked file that changed too
session_duration	Anytime	How long the session has been tracked
invalidate_source	Manually	Marks a source stale on demand

check_staleness is the core. It never answers only about the one file you asked about. It reports the full set of tracked files that have drifted, so the agent cannot stay blind to a change it did not think to check.

How it works

since stamps every file read with its mtime and a SHA-256 hash. On any later call it compares stored fingerprints against the current file: mtime first because it is fast, full hash only if mtime moved. No daemon, no polling, no background process. Just a comparison against disk at the next turn, which is why it catches changes the agent's own cached view cannot.

---

Also: temporal context for chat apps

The same primitive, aimed at conversations instead of files. Wrap your chat function and the model sees a timeline: when each message happened, how long the gaps were, and what context has gone stale.

from since import Store, since_time
from openai import OpenAI

store = Store("~/.since/chat.db")
client = OpenAI()

@since_time(store=store, timezone="Asia/Kolkata")
def chat(messages):
    return client.chat.completions.create(model="gpt-4o-mini", messages=messages)

resp = chat(messages=[{"role": "user", "content": "hello"}])
print(resp.choices[0].message.content)

The model receives a compact time block before each turn:

Now:      Wed Jul 01, 02:36 AM (night)
Session:  9h 2m total, 4m active across 3 sittings, 8 messages
Gap:      6h since the last message

So instead of "I don't have information about previous conversations," it can say "welcome back, it has been about 6 hours since we last spoke."

The decorator reads the OpenAI response shape by default. For other providers, pass an extract_reply function that returns the reply text from your provider's response object.

Requirements

• Python 3.10+
• Zero dependencies

Install

pip install pysince

The PyPI name is pysince because since was already taken. You import it, and the repo is named, since.