MCP tool catalogs and oversized results consume agent context. Truncation can discard the source needed for inspection and continued work.
MCP Slim Guard delivers eligible MCP content as a compact view and stores one immutable snapshot. When the agent needs the source, read_result reads the snapshot. One upstream call covers the whole path.
One Upstream Call, Two Delivery Paths
The current Alpha provides two integration surfaces:
- Generic progressively exposes tools through
find_tool,call_tool, andread_result. - Native keeps the original names of authorized tools and decides whether to pass through or compact the result at delivery time.
Both surfaces use the same delivery contract. Slim Guard forwards the selected arguments unchanged and runs the upstream tool once per request. Eligible long text, uniform JSON, and log-like results produce a compact view. Other results keep the upstream format.
The compact view carries a recovery reference. read_result uses it to read the immutable snapshot, keeping the upstream call count at one.
Standard Benchmark: 71,388 → 17,007 Tokens
The frozen standard benchmark covers 12 deterministic tools and 24 bilingual tasks. It uses o200k_base to count the MCP exposure and normal task path:
| Metric | Direct | MCP Slim Guard |
|---|---|---|
| Normal-path tokens | 71,388 | 17,007 |
| Tasks completed | 24/24 | 24/24 |
| Upstream calls | 24 | 24 |
The normal path used 76.18% fewer MCP tokens. All 24 tasks completed with one upstream call per task.
The public release’s benchmark summary describes the test scope, o200k_base counting method, and aggregate results. The originally linked task-level evidence document is not publicly accessible as of 3 October 2026.
A separate synthetic stress test with 100 tools and an 8,000-row result recorded an upper bound of 99.7%, showing the delivery behavior at an extreme catalog and result size.
Current Host Support
| Host | Current Alpha surface |
|---|---|
| Codex | Native preferred, Generic fallback |
| Claude Code | Generic |
| VS Code | Preview |
| OpenCode | Post-Alpha |
Slim Guard focuses on reversible MCP result delivery. Authorization, exact routing, and audit behavior serve that delivery path.
Install the Alpha
pnpm add -g mcp-slim-guard@alpha
Use the GitHub README for host-specific setup, migration, and rollback instructions. The current release is 0.1.1-alpha.1 and requires Node.js 20 or newer.
Same upstream call. Exact recovery.