MCP Server by jerbly · Pull Request #1113 · open-telemetry/weaver

jerbly · 2026-01-05T01:55:44Z

This PR adds weaver registry mcp an MCP (Model Context Protocol) server that exposes the semantic conventions registry to LLMs. This enables natural language queries for finding and understanding conventions while writing instrumentation code.

Tool	Description
`search`	Search across all registry items (attributes, metrics, spans, events, entities)
`get_attribute`	Get detailed information about a specific attribute by key
`get_metric`	Get detailed information about a specific metric by name
`get_span`	Get detailed information about a specific span by type
`get_event`	Get detailed information about a specific event by name
`get_entity`	Get detailed information about a specific entity by type
`live_check`	Validate telemetry samples against the registry

…n MCP tools and handlers

…r live check tool

…metric, search, and span tools

…icies and preprocessor support

…al-types

codecov · 2026-01-05T02:36:30Z

Codecov Report

❌ Patch coverage is 87.23404% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.3%. Comparing base (b3f81ed) to head (bfafb6b).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/weaver_mcp/src/lib.rs	11.1%	16 Missing ⚠️
crates/weaver_mcp/src/service.rs	97.4%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1113     +/-   ##
=======================================
+ Coverage   79.2%   80.3%   +1.0%     
=======================================
  Files        103     105      +2     
  Lines       7992    8126    +134     
=======================================
+ Hits        6333    6528    +195     
+ Misses      1659    1598     -61

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jsuereth · 2026-01-08T18:14:05Z

crates/weaver_mcp/src/service.rs

+/// - `get_entity` - Get a specific entity by type
+/// - `live_check` - Validate telemetry samples against the registry
+#[derive(Clone)]
+pub struct WeaverMcpService {


I know this may be crazy, but is there any chance we can re-use the vanilla API server and just "wrap" API methods with MCP definitions instead of having two instances of serving / application flow?

I think there's a LOT of commonality between the two pieces, and it'd be ideal if we could share it.

Wrapping a web api with mcp is an anti-pattern. I did move all the internals of search and get* into the weaver_search crate to make it common. I think it's likely they'll diverge, for example I'm experimenting with multiple tools for live-check.

Wrapping a web api with mcp is an anti-pattern.

Interesting - tell me more?

I'm suggesting MCP is basically API++. Where we can delegate to API functions we should. If you add more that's great.

E.g. I'd be nice if we had a consistent "AppContext" structure that has our Arc<State> in it and a set of methods on this that both the MCP + API server would use.

I'm not suggesting we directly call the API from MCP - just that we take small amount of time to but in a shared abstraction they can both use to interact with a 'served weaver' thing.

Actually @lquerel first pointed this out to me in this comment #798 (comment) where I had a similar idea to you. Subsequently I have read this same advice quite a few times. The video link is good, there's also a good reddit thread if I recall correctly.

Did you see that I moved the common internals to the weaver_search crate?

Thanks for the link! I'll take a look.

Did you see that I moved the common internals to the weaver_search crate?

I did not, but that's great!

I was actually thinking of naming the create weaver_debugger or some such - i.e. if I were to add "jq", "rego" or "jinja" debugging tools, what crate should that live in?

weaver_devtools??

Oooh - I like that better!

jsuereth

Thanks for all the cleanups!

I think this is good to merge, but we should track some work to make it clear how "extensions" are loaded in weaver, e.g. Rego policies.

jsuereth · 2026-01-11T18:50:53Z

crates/weaver_mcp/src/service.rs

+
+/// MCP service for the semantic convention registry.
+///
+/// This service exposes 7 tools for querying and validating against the registry:


Nit - let's update this to say exposes tools for querying, debugging and validating against the registry. For example:

jsuereth · 2026-01-11T18:52:31Z

src/registry/mcp.rs

+    #[command(flatten)]
+    pub diagnostic: DiagnosticArgs,
+
+    /// Advice policies directory. Set this to override the default policies.


My only remaining hangup on this PR is these two advice_* arguments. Basically I think our current "when to load rego, jq + jinja" story is a bit off. It's unclear when weaver.yml controls it, when you pull from the same directory as a registry and when you specify via the command line.

I think that's bigger than the scope of this PR, but let's sort that out going forward.

I agree, also how to specify builtins to use AND custom, or when to override the builtin with a custom. For example, often I want all the otel policies plus my own on top.

jerbly added 19 commits December 31, 2025 22:15

initial mcp impl

13e8610

fixed notificaiton protocol, added docs

f72bda9

added live-check tool

2ee2847

refactor: replace registry lookups with O(1) search context methods i…

6198f89

…n MCP tools and handlers

feat: add schemars dependency and integrate JSON schema generation fo…

b373e09

…r live check tool

feat: integrate JSON schema generation for attribute, entity, event, …

7c1b005

…metric, search, and span tools

feat: enhance MCP server live-check tool with configurable advice pol…

a789c0d

…icies and preprocessor support

refactor: update tool execution methods to use mutable self references

cbcd6ab

migrated to rmcp

f2a2b2e

feat: add README for MCP server integration with LLMs

85ed3a8

feat: add allowed external types configuration for cargo-check-extern…

5af6d20

…al-types

unit tests

533706a

added search and mcp test coverage

9152449

fmt

59eb339

changelog

10c871e

better changelog

e766140

remove claude references

66d93fb

Merge branch 'main' of https://github.com/open-telemetry/weaver into mcp

752b7db

changelog fix

9e12be5

jerbly marked this pull request as ready for review January 5, 2026 02:41

jerbly requested a review from a team as a code owner January 5, 2026 02:41

jerbly added 2 commits January 5, 2026 15:03

fixed commands in readme

5511a63

improve search tool description

422ffa3

jerbly mentioned this pull request Jan 7, 2026

Add Collector Model Context Protocol (MCP) project proposal open-telemetry/community#3128

Merged

jsuereth reviewed Jan 8, 2026

View reviewed changes

jerbly added 3 commits January 10, 2026 14:05

Merge branch 'main' of https://github.com/open-telemetry/weaver into mcp

ec8091a

fixes following structure changes to ForgeResolvedRegistry

0191b9e

removed schemars <v1 workarounds

7eb42cb

jsuereth approved these changes Jan 11, 2026

View reviewed changes

comment update

bfafb6b

jerbly merged commit 85bf53c into open-telemetry:main Jan 11, 2026
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MCP Server#1113

MCP Server#1113
jerbly merged 25 commits intoopen-telemetry:mainfrom
jerbly:mcp

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