feat(langchain): add docs on dynamic tools #643

christian-bromann · 2025-09-24T19:37:33Z

This docs page covers the advanced usage of "Dynamic Tools" explaining how users can implement smart ways to choose tools based on context (simple) or semantic similarity (advanced).

Happy to add Python code examples if we are ok with current structure.

github-actions · 2025-09-24T19:38:41Z

Preview ID generated: preview-cbdyna-1758742693-3b83878

eyurtsev

let's move to middleware

src/oss/langchain/dynamic-tools.mdx

github-actions · 2025-09-24T20:59:24Z

Preview ID generated: preview-cbdyna-1758747534-6b63fd5

christian-bromann · 2025-09-24T21:06:56Z

Update:

updated examples based on provided feedback
added Python translations (please review)
moved to middleware docs

github-actions · 2025-09-24T21:07:59Z

Preview ID generated: preview-cbdyna-1758748047-d12eb3e

github-actions · 2025-09-25T00:47:25Z

Preview ID generated: preview-cbdyna-1758761214-5616d01

Copilot

Pull Request Overview

This PR adds comprehensive documentation for dynamic tool selection in LangChain, addressing how to efficiently manage large tool catalogs by dynamically selecting relevant subsets per turn. This feature helps reduce context pressure, improve model performance, and decrease latency/costs when working with hundreds or thousands of tools.

Key changes include:

Adding a complete "Dynamic tools" section explaining the problem and solution approach
Providing both simple context-based and advanced semantic similarity-based tool selection examples
Including production optimization strategies and design guidelines

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/oss/langchain/structured-output.mdx	Fixes import path for toolStrategy and providerStrategy from langchain/agents to langchain
src/oss/langchain/middleware.mdx	Adds comprehensive dynamic tools documentation with examples, optimization strategies, and design guidelines

Copilot · 2025-09-25T00:50:01Z

src/oss/langchain/middleware.mdx

+            runtime.context.vcs_provider if getattr(runtime, "context", None) else "github"
+        ).lower()
+        active = [gitlab_create_issue] if provider == "gitlab" else [github_create_issue]
+        request.tools = active  # [!code highlight]


The init_embeddings function call appears to use an incorrect API. Based on standard LangChain patterns, this should likely be OpenAIEmbeddings(model="text-embedding-3-small") or similar constructor pattern rather than an init_embeddings function.

Copilot · 2025-09-25T00:50:02Z

src/oss/langchain/middleware.mdx

+    return {"url": f"https://github.com/{repo}/issues/1", "title": title}
+
+
+# GitLab tools


This import path appears incorrect. The standard LangChain import for OpenAI embeddings would be from langchain_openai import OpenAIEmbeddings rather than importing an init_embeddings function.

Copilot · 2025-09-25T00:50:02Z

src/oss/langchain/middleware.mdx

+
+// Choose tools based on user context (e.g., vcsProvider = "github" | "gitlab")
+const vcsToolGate = createMiddleware({
+  name: "VcsToolGate",


[nitpick] The humorous reference to 'travel with a banana' in the visa requirements example may confuse users who expect realistic documentation examples. Consider using a more realistic visa requirement example.

Suggested change

name: "VcsToolGate",

`Travelers from ${country} are required to obtain a visa and present a valid passport upon entry.`,

github-actions · 2025-09-25T00:50:50Z

Preview ID generated: preview-cbdyna-1758761420-9d67015

Quick patch that documents that user can define tools in middleware as well as ModelRequest now takes a list of tool names instead of tool instances. Co-authored-by: Lauren Hirata Singh <lauren@langchain.dev>

github-actions · 2025-09-29T10:59:41Z

Preview ID generated: preview-cbdyna-1759143549-68c15ff

christian-bromann · 2025-09-30T03:53:19Z

@eyurtsev do you think this is good to go?

github-actions · 2025-09-30T15:36:51Z

Preview ID generated: preview-cbdyna-1759246583-d530ae5

Copilot

Pull Request Overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

Copilot · 2025-09-30T15:37:11Z

src/oss/langchain/middleware.mdx

  - `{ type: "function", function: { name: string } }`: The model will use the specified function.
 :::
- `tools` (list of `BaseTool`): the tools to use for this model call
+- `tools` (list of strings): the tool names to use for this model call


The documentation change from 'list of BaseTool' to 'list of strings' appears to contradict the Python example on line 1176 where request.tools = [tool.name for tool in active_tools] suggests tools should be tool names (strings), not tool objects. However, this inconsistency should be verified against the actual API to ensure the documentation accurately reflects the expected parameter type.

Copilot · 2025-09-30T15:37:11Z

src/oss/langchain/middleware.mdx

+full_catalog = [book_flight, lookup_visa_requirements, local_weather]
+
+# 2) Precompute and cache embeddings for tool metadata
+embedder = init_embeddings("openai:text-embedding-3-small")


The init_embeddings function is not a standard LangChain API. This should likely be OpenAIEmbeddings(model='text-embedding-3-small') or the appropriate embeddings initialization method from the LangChain library.

Copilot · 2025-09-30T15:37:11Z

src/oss/langchain/middleware.mdx

+        content = (
+            last["content"] if isinstance(last, dict) else getattr(last, "content", None)
+        )


The message content extraction logic is overly complex and fragile. Consider using a more robust approach like content = last.content if hasattr(last, 'content') else (last.get('content') if isinstance(last, dict) else None) or define a helper function for message content extraction.

Suggested change

content = (

last["content"] if isinstance(last, dict) else getattr(last, "content", None)

)

content = last.content if hasattr(last, "content") else (last.get("content") if isinstance(last, dict) else None)

Copilot · 2025-09-30T15:37:12Z

src/oss/langchain/middleware.mdx

+const toolVectors = await embedder.embedDocuments(toolTexts);
+
+type CatalogItem = { tool: StructuredTool; vector: number[] };
+const catalog: CatalogItem[] = fullCatalog.map((tool, i) => ({
+  tool,
+  vector: toolVectors[i],
+}));
+
+function cosineSimilarity(a: number[], b: number[]) {
+  const dot = a.reduce((s, v, i) => s + v * b[i], 0);
+  const na = Math.hypot(...a);
+  const nb = Math.hypot(...b);
+  return na && nb ? dot / (na * nb) : 0;
+}
+
+async function selectTopKBySimilarity(query: string, k = 6) {
+  const qv = await embedder.embedQuery(query);
+  return catalog
+    .map((c) => ({ c, score: cosineSimilarity(qv, c.vector) }))
+    .sort((a, b) => b.score - a.score)
+    .slice(0, k)
+    .map(({ c }) => c.tool);
+}
+


The await keyword is used in a non-async context. The embedding computation should either be wrapped in an async function or moved to an initialization phase that properly handles the asynchronous operation.

Suggested change

const toolVectors = await embedder.embedDocuments(toolTexts);

type CatalogItem = { tool: StructuredTool; vector: number[] };

const catalog: CatalogItem[] = fullCatalog.map((tool, i) => ({

tool,

vector: toolVectors[i],

}));

function cosineSimilarity(a: number[], b: number[]) {

const dot = a.reduce((s, v, i) => s + v * b[i], 0);

const na = Math.hypot(...a);

const nb = Math.hypot(...b);

return na && nb ? dot / (na * nb) : 0;

}

async function selectTopKBySimilarity(query: string, k = 6) {

const qv = await embedder.embedQuery(query);

return catalog

.map((c) => ({ c, score: cosineSimilarity(qv, c.vector) }))

.sort((a, b) => b.score - a.score)

.slice(0, k)

.map(({ c }) => c.tool);

}

async function main() {

const toolVectors = await embedder.embedDocuments(toolTexts);

type CatalogItem = { tool: StructuredTool; vector: number[] };

const catalog: CatalogItem[] = fullCatalog.map((tool, i) => ({

tool,

vector: toolVectors[i],

}));

function cosineSimilarity(a: number[], b: number[]) {

const dot = a.reduce((s, v, i) => s + v * b[i], 0);

const na = Math.hypot(...a);

const nb = Math.hypot(...b);

return na && nb ? dot / (na * nb) : 0;

}

async function selectTopKBySimilarity(query: string, k = 6) {

const qv = await embedder.embedQuery(query);

return catalog

.map((c) => ({ c, score: cosineSimilarity(qv, c.vector) }))

.sort((a, b) => b.score - a.score)

.slice(0, k)

.map(({ c }) => c.tool);

}

// You can now use selectTopKBySimilarity, catalog, etc. here

}

main();

feat(langchain): add docs on dynamic tools

18fc9e6

github-actions bot added langchain For docs changes to LangChain oss labels Sep 24, 2025

eyurtsev reviewed Sep 24, 2025

View reviewed changes

src/oss/langchain/dynamic-tools.mdx Outdated Show resolved Hide resolved

src/oss/langchain/dynamic-tools.mdx Outdated Show resolved Hide resolved

src/oss/langchain/dynamic-tools.mdx Outdated Show resolved Hide resolved

eyurtsev reviewed Sep 24, 2025

View reviewed changes

src/oss/langchain/dynamic-tools.mdx Outdated Show resolved Hide resolved

src/oss/langchain/dynamic-tools.mdx Outdated Show resolved Hide resolved

src/oss/langchain/dynamic-tools.mdx Outdated Show resolved Hide resolved

src/oss/langchain/dynamic-tools.mdx Outdated Show resolved Hide resolved

add python examples

8a77e0e

move to middleware

091a1ff

update examples

6b2e755

vercel bot had a problem deploying to Preview September 25, 2025 00:46 Failure

christian-bromann mentioned this pull request Sep 25, 2025

chore(langchain/createAgent): add examples for dynamic tools langchain-ai/langchainjs#9040

Merged

christian-bromann marked this pull request as ready for review September 25, 2025 00:49

christian-bromann requested a review from lnhsingh as a code owner September 25, 2025 00:49

Copilot AI review requested due to automatic review settings September 25, 2025 00:49

christian-bromann requested a review from katmayb as a code owner September 25, 2025 00:49

Merge branch 'main' into cb/dynamic-tools

d50037d

Copilot AI reviewed Sep 25, 2025

View reviewed changes

vercel bot had a problem deploying to Preview September 25, 2025 00:50 Failure

fix(langchain/middleware): document that user can define tools (#653)

810c68c

Quick patch that documents that user can define tools in middleware as well as ModelRequest now takes a list of tool names instead of tool instances. Co-authored-by: Lauren Hirata Singh <lauren@langchain.dev>

vercel bot had a problem deploying to Preview September 29, 2025 10:59 Failure

Merge branch 'main' into cb/dynamic-tools

9e28b21

Copilot AI review requested due to automatic review settings September 30, 2025 15:35

Copilot AI reviewed Sep 30, 2025

View reviewed changes

		return {"url": f"https://github.com/{repo}/issues/1", "title": title}


		# GitLab tools

	name: "VcsToolGate",
	`Travelers from ${country} are required to obtain a visa and present a valid passport upon entry.`,

feat(langchain): add docs on dynamic tools #643

Are you sure you want to change the base?

feat(langchain): add docs on dynamic tools #643

Conversation

christian-bromann commented Sep 24, 2025

Uh oh!

github-actions bot commented Sep 24, 2025

Uh oh!

eyurtsev left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

github-actions bot commented Sep 24, 2025

Uh oh!

christian-bromann commented Sep 24, 2025

Uh oh!

github-actions bot commented Sep 24, 2025

Uh oh!

github-actions bot commented Sep 25, 2025

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull Request Overview

Reviewed Changes

Uh oh!

Copilot AI Sep 25, 2025

Choose a reason for hiding this comment

Uh oh!

Copilot AI Sep 25, 2025

Choose a reason for hiding this comment

Uh oh!

Copilot AI Sep 25, 2025

Choose a reason for hiding this comment

Uh oh!

github-actions bot commented Sep 25, 2025

Uh oh!

github-actions bot commented Sep 29, 2025

Uh oh!

christian-bromann commented Sep 30, 2025

Uh oh!

github-actions bot commented Sep 30, 2025

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull Request Overview

Uh oh!

Copilot AI Sep 30, 2025

Choose a reason for hiding this comment

Uh oh!

Copilot AI Sep 30, 2025

Choose a reason for hiding this comment

Uh oh!

Copilot AI Sep 30, 2025

Choose a reason for hiding this comment

Uh oh!

Copilot AI Sep 30, 2025

Choose a reason for hiding this comment

Uh oh!

Uh oh!