The full argument lives in the blog post Just Give the Agent Files. The short version:
- MCP lets the agent pull. It is not how the world pushes a signal to the agent. For push you need webhooks, and making a single agent proactive against Linear means a public endpoint, HMAC verification, a queue, deduplication, and retries. Then repeat per provider. Relayfile does that once and hands the agent a normalized file event instead.
- Stacked MCP tools bloat context. Tool definitions can consume tens of thousands of tokens before any work begins. Files load nothing — context cost is exactly what the agent opens.
- The workspace is just files. Every provider mounts at a well-known path. The agent explores with
ls, reads withcat, searches withgrep— no per-provider schema to learn. - Writebacks are files too. The agent writes a file; Relayfile handles provider auth, validation, retries, and the audit trail. No API call from the agent.
- Agents coordinate through the filesystem. Writes propagate to every other agent in sub-second time, scoped by ACL. When agent A writes, agent B sees it on the next read. No message bus.
The benchmark
We ran "what did I work on yesterday across GitHub, Linear, and Notion?" head-to-head against MCP, same prompt and accounts, across three Claude models. After adding by-* index directories and a pre-computed digests/yesterday.md, the filesystem won decisively:
| Model | MCP cost | Relayfile cost | MCP turns | RF turns |
|---|---|---|---|---|
| Opus | $0.44 | $0.25 | 9 | 4 |
| Sonnet | $0.27 | $0.07 | 18 | 4 |
| Haiku | failed¹ | $0.06 | — | 4 |
¹ MCP Haiku asked for clarification instead of acting. Relayfile Haiku completed the task.
The digest is one file read that replaces 25 individual provider queries. Every structural improvement to the mount makes every future run cheaper — with MCP you are stuck at whatever the API returns. The full write-up shows all three rounds, including the naive first pass where files lost.
When a typed tool still wins
Files are not always the answer. For a single provider, a single agent, and a one-shot action that needs server-side validation, a dedicated MCP that enforces the shape at call time is simpler. The two compose: Relayfile for reads, synthesis, and the multi-provider substrate; an MCP for typed one-shot writes. See Comparison.