# afterMCPExecution return value is discarded, and postToolUse carries no MCP server identity

**URL:** <https://forum.cursor.com/t/aftermcpexecution-return-value-is-discarded-and-posttooluse-carries-no-mcp-server-identity/167261>\
**Category:** Feature Requests\
**Tags:** cli, mcp, hooks\
**Created:** [August 2, 2026, 1:25pm UTC](https://forum.cursor.com/t/aftermcpexecution-return-value-is-discarded-and-posttooluse-carries-no-mcp-server-identity/167261 "2026-08-02T13:25:39Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![EilonGoldberg](https://avatars.discourse-cdn.com/v4/letter/e/e5b9ba/32.png) [@EilonGoldberg](https://forum.cursor.com/u/EilonGoldberg)\
**Post date:** [August 2, 2026, 1:25pm UTC](https://forum.cursor.com/t/aftermcpexecution-return-value-is-discarded-and-posttooluse-carries-no-mcp-server-identity/167261/1 "2026-08-02T13:25:39Z")

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There is no post-execution hook that can both (a) tell which MCP server produced a tool result and (b) act on it. The two halves live on two different hooks.

**Detail**

At the MCP tool-call site, two hooks fire back to back:

- `afterMCPExecution` receives `mcp_server_name` and `mcp_server_url`, but its return value is discarded.
- `postToolUse` honors `updated_mcp_tool_output` (replaces the result the model sees), but its payload carries no MCP server fields — only `tool_name`, `tool_input`, `tool_output`, `duration`, `tool_use_id`.

From cursor-agent `2026.07.23-e383d2b`:

```js
// payload `i` spreads `b` = { mcp_server_name, mcp_server_url }
yield this.hookExecutor.executeHookForStep(u._E.afterMCPExecution, i); // return value not assigned
const a = yield this.firePostToolUse(e, l, f, p, n, s, d, h);
if (void 0 !== a?.updated_mcp_tool_output) { /* result is substituted */ }

```

`firePostToolUse` builds its payload as `{...t, tool_name, tool_input, tool_output, duration, tool_use_id}` — `b`, which holds the server fields, is not spread in.

`beforeMCPExecution` has both halves (it gets `mcp_server_name` / `mcp_server_url` / `url` / `command` **and** honors `permission: "deny"`), so the gap is only on the post-execution side.

**Why this matters**

Policy about MCP tool _results_ is per-server: whether a result is acceptable depends on which server returned it. A tool result is also an injection vector into the model’s context, so the moment before the model reads it is where that policy has to apply. Today the decision can be made on `afterMCPExecution` but not enforced, or enforced on `postToolUse` but not made.

To be clear, this is not a request to un-run the call — it has already executed and that can’t be reversed. It is only about withholding or replacing the result before the model reads it, which `postToolUse` already supports.

**Either change closes the gap**

1. Honor `updated_mcp_tool_output` from `afterMCPExecution`’s return value, as `postToolUse` already does; or
2. Add `mcp_server_name` / `mcp_server_url` to the `postToolUse` payload for MCP tools.

(2) looks like the smaller change.

**Environment**

cursor-agent `2026.07.23-e383d2b`, macOS.

Also filed at [Hooks: `afterMCPExecution` return value is discarded, and `postToolUse` carries no MCP server identity · Issue #50 · cursor/cookbook · GitHub](https://github.com/cursor/cookbook/issues/50) for visibility.

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**Author:** ![mohitjain](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/mohitjain/32/100229_2.png) [@mohitjain](https://forum.cursor.com/u/mohitjain)\
**Post date:** [August 5, 2026, 1:50pm UTC](https://forum.cursor.com/t/aftermcpexecution-return-value-is-discarded-and-posttooluse-carries-no-mcp-server-identity/167261/6 "2026-08-05T13:50:52Z")

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Hey there,

To confirm each side:

- `beforeMCPExecution` is the one hook today that carries both the server identity (`mcp_server_name` / `mcp_server_url`) and the ability to act (`permission: "deny"`), so per-server gating before a call runs works now.
- Post-execution, `afterMCPExecution` is observation-only, and `postToolUse` is the hook that can substitute a result (`updated_mcp_tool_output`) - but it doesn’t currently carry the MCP server fields, so per-server policy on the _result_ isn’t expressible today. That lines up with what you found.

Between your two options, adding `mcp_server_name` / `mcp_server_url` to the `postToolUse` payload is the cleaner fit, since the after-hooks are intentionally observation-only.

We’ll be tracking this thread to gauge interest, which helps our team prioritize - so if others want per-server result policies, please chime in. No timeline to share yet, but I’ll post back here when there’s an update. (And thanks for cross-filing on the cookbook.)

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**Author:** ![system](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/system/32/99069_2.png) [@system](https://forum.cursor.com/u/system)\
**Post date:** [September 4, 2026, 1:51pm UTC](https://forum.cursor.com/t/aftermcpexecution-return-value-is-discarded-and-posttooluse-carries-no-mcp-server-identity/167261/7 "2026-09-04T13:51:08Z")

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