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feat: add mcp_lazy mode for on-demand MCP tool loading - #8771

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xHeaven wants to merge 7 commits into
anomalyco:devfrom
xHeaven:mcp-search
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feat: add mcp_lazy mode for on-demand MCP tool loading#8771
xHeaven wants to merge 7 commits into
anomalyco:devfrom
xHeaven:mcp-search

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@xHeaven

@xHeavenxHeaven commented Jan 16, 2026•
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Closes#8625.

What does this PR do?

Adds a new experimental.mcp_lazy config option that prevents MCP tools from being loaded into context automatically. Instead, a new mcp_search tool is provided to discover and call MCP tools on-demand.

This reduces context usage for users with many MCP servers configured. When enabled:

  • MCP tools are excluded from the tool list sent to the model
    • Instead, available MCP servers are injected into the system prompt in a compact format.
  • The mcp_search tool allows listing, searching, describing, and calling MCP tools
  • MCP servers show "Lazy" status in the /mcp dialog

The injected prompt:

<mcp_servers>
Available MCP servers: context7, firecrawl, playwright
Use mcp_search tool to discover and call tools from these servers.
</mcp_servers>

How did you verify your code works?

  • Tested with experimental.mcp_lazy: true in config
  • Verified MCP tools are not in context and mcp_search appears instead
  • Tested all operations: list, search, describe, call
  • Confirmed servers connect on-demand when calling tools

The tests were manual, there are no actual tests included here.

@github-actions

github-actionsBot commented Jan 16, 2026

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Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

  1. Open an issue describing the bug/feature (if one doesn't exist)
  2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

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github-actionsBot commented Jan 16, 2026

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The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

@DeveloperJose

DeveloperJose commented Jan 18, 2026

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#8177 also proposes something similar

@xHeaven

xHeaven commented Jan 18, 2026

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#8177 also proposes something similar

Damn, I completely missed that one. Our solutions differ a bit, I guess it comes down to preference. Also, honestly, I'm not sure I'd call either solution "complete", more like an idea of how this feature could be implemented.

@DeveloperJose

DeveloperJose commented Jan 19, 2026

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There was also this one in November that was closed, #4717

Slightly different and with the idea of loading tools for certain turns and then unloading them

@spoons-and-mirrors

spoons-and-mirrors commented Jan 19, 2026

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yeah #4717 was a simpler implementation that just worked, maybe not the most feature full approach but did the trick fine. I closed it because it wasn't getting any attention and i wanted to help declutter opencode's growing PR number :D

@xHeaven

xHeaven commented Jan 19, 2026

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yeah #4717 was a simpler implementation that just worked, maybe not the most feature full approach but did the trick fine. I closed it because it wasn't getting any attention and i wanted to help declutter opencode's growing PR number :D

That's probably what's going to happen to this PR, too. This is a great feature - probably not the best implementation -, but it's not getting the attention I would expect for something like this. I'm hoping the core contributors will pick up on it and make a better implementation.

@DeveloperJose

DeveloperJose commented Jan 19, 2026

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There's another proposed implementation here https://github.com/famitzsy8/opencode-tool-search-tool

By @famitzsy8

If we are going to keep pushing this idea forward we might need to consolidate all the duplicate issues and PRs.

@DeveloperJoseDeveloperJose mentioned this pull request Jan 19, 2026
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@thdxr
thdxrforce-pushed the dev branch 3 times, most recently from f1ae801 to 08fa7f7CompareJanuary 30, 2026 14:37
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@atanasna

atanasna commented Feb 10, 2026

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Can you explain how this works with permissions, please?
If I have an subagent that only needs to use tools A,B,C from an MCP, but not tools D,E will the mcp_search only see A,B and C ?

@KennyDizi

KennyDizi commented Feb 11, 2026

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Looking forward to this PR being merged.

@strawberrymelonpanda

strawberrymelonpanda commented Feb 21, 2026

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Looking forward to this PR being merged.

If you're interested in it, as I am, probably best to just merge it locally. I don't know how OpenCode chooses which PRs to merge, but given the radio silence, I'd say odds aren't great.

vbuccigrossi pushed a commit to vbuccigrossi/opencode that referenced this pull request Mar 7, 2026
EBrown@claude
feat: port remaining Tier 1+2 upstream fixes and features
63e7373
Tier 1 bug fixes:
- Fix O(n²) bash output concatenation with StreamingOutput class (anomalyco#9693)
- Fix memory leaks in Bus.once, Format, Plugin, ShareNext, Bootstrap (anomalyco#13514)
- Fix FileTime race condition using actual file mtime instead of JS clock
- Free memory on compaction prune: clear output/attachments/metadata (anomalyco#7049)
- Throttle reasoning-delta storage writes to 50ms intervals (anomalyco#11328)
- Handle SIGHUP/SIGTERM to prevent orphaned processes (anomalyco#12718)
- Add process.once("close") handler for bash tool reliability
Tier 2 features:
- Support 1M context window for Anthropic models via beta header (anomalyco#14375)
- Input-only token counting for compaction with limit.input models
- MCP lazy loading: on-demand tool discovery via mcp_search tool (anomalyco#8771)
- MCP servers listed in system prompt when lazy mode enabled
- StreamingOutput: output_filter regex for build diagnostics
- LSP server cleanup callback for temp directory removal
- Extract formatSize utility from uninstall to shared util/format
- GitHub CI: fix Bus subscription leak in session event handler
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
@mustafa89

mustafa89 commented Apr 7, 2026

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Any chances of this getting merged ?

@DrDexter6000DrDexter6000 mentioned this pull request Apr 7, 2026
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@hchangjaehchangjae mentioned this pull request Apr 20, 2026
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@GordianSch

GordianSch commented May 21, 2026

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Desperately waiting for a merge.

@mustafa89

mustafa89 commented May 21, 2026

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Dont worry. They are currently focusing on adding "ding" sounds on agent completion.

Wayy more important than this.

@github-actionsgithub-actionsBot mentioned this pull request Jun 8, 2026
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@rutmehta

rutmehta commented Aug 5, 2026

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can we merge this yet?

@rekram1-node

rekram1-node commented Aug 18, 2026

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We added support for codemode instead of a tool search, you can enable with: OPENCODE_EXPERIMENTAL_CODE_MODE=true

v2 of opencode ships with it enabled by default

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[FEATURE]:Add mcp search tool, reduce mcp tool occupying a lot of context

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@xHeaven@DeveloperJose@spoons-and-mirrors@atanasna@KennyDizi@strawberrymelonpanda@mustafa89@GordianSch@rutmehta@rekram1-node