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No universal MCP rule caps a server at 90 tools. The MCP tools specification supports paginated discovery, so a catalog problem above that size is more likely to involve a particular client’s pagination or aggregation behavior, prompt/context pressure, or the model’s ability to select the right tool—not an established protocol ceiling. The key is to identify which layer fails.

Does MCP limit a server to 90 tools?

No. The MCP specification’s tools/list operation supports pagination and does not set a maximum of 90 tools. A server that declares the tools capability must return the tools currently available to the requesting client. The list may vary with authorization, but the specification says it must not vary per connection or as a side effect of other requests on that connection. See the MCP Tools specification.

That protocol-level behavior does not guarantee that every host or SDK will retrieve, retain, display, or use an arbitrarily large catalog successfully. “90+ tools” is therefore not a general MCP breaking point. It can describe a failure in a particular implementation, but the host, SDK, version, and observed failure need to be identified before assigning a threshold.

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Where a large tool catalog can fail

Tool discovery involves distinct layers. A failure at one does not show that the MCP server itself has reached a protocol limit.

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  • Server response: The server may fail to return a valid page or may not implement pagination correctly. This is a server or protocol-implementation issue, not a standard 90-tool cap.
  • Client pagination or aggregation: A client may stop following pages, impose a page-count safeguard, or fail while combining results. This can leave tools undiscovered even though the server supports pagination.
  • Prompt and context pressure: A host may pass many tool names and descriptions to a model at once. A large catalog can consume context and make the relevant choices harder to distinguish.
  • Tool selection: The tools may be available to the model, but it may choose an unsuitable one or miss the right one among similar candidates. That is a selection-quality issue, not a listing failure.

What the TypeScript SDK’s 64-page default means

The MCP TypeScript SDK documents that listTools() called without a cursor automatically traverses pages and aggregates the results. That automatic path has a default listMaxPages limit of 64 pages. Calling with an explicit cursor fetches an individual page without that automatic aggregation cap. See the MCP TypeScript SDK documentation.

64 is a page count, not a tool count. The cited documentation does not establish how many tools each page contains, so it cannot be converted into a maximum number of tools. Nor does this SDK behavior establish the limit for other MCP clients. If a catalog appears incomplete, check whether the client traversed all pages and whether its aggregation settings stopped the process.

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Why more tools can make selection harder

Even when discovery succeeds, a model can struggle to choose among a growing set of candidates—especially when descriptions overlap or tools have similar names. One 2026 paper, MCP Server Architecture Patterns for LLM-Integrated Applications, reports selection accuracy below 90% at 10–15 tools for Claude Haiku 4.5 and at 20–30 tools for Sonnet 4. Those are results reported for the paper’s tested settings, not a universal threshold, an MCP requirement, or evidence that every model fails at those catalog sizes. The available result does not establish that the findings generalize to other models, descriptions, tasks, or hosts. See the arXiv paper listing.

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How to diagnose a 90-plus-tool problem

  1. Confirm the failure mode. Determine whether the server errors, the client returns an incomplete list, the host omits tools from the model’s available choices, or the model selects the wrong tool. Record the exact host and SDK versions and a reproducible task.
  2. Check page traversal. Inspect the client’s tools/list requests and cursors. Confirm that it requests subsequent pages and does not stop at an implementation-specific page limit. If using the TypeScript SDK’s automatic aggregation, account for its documented default of 64 pages.
  3. Compare the server’s available tools with the client’s catalog. Check authorization context and the returned pages. The specification permits availability to vary according to authorization, so compare like with like.
  4. Test selection separately from discovery. If every tool is listed but the wrong one is chosen, try representative tasks with the actual tool descriptions and task mix. A successful list response does not prove reliable model selection.
  5. Reduce the candidate set and retest. Apply filtering or on-demand discovery, then compare whether the same tasks become easier to route. Treat this as an implementation test, not proof of a protocol limit.

Ways to manage a large catalog

Filter before registering tools

Application-side filtering can register only the tools relevant to a user, workflow, or task. This reduces the number of candidates presented at once, but requires the application to choose and maintain the filtering rules. AWS guidance describes filtering as one approach to managing large tool sets: AWS machine-learning guidance.

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Retrieve tools on demand

Instead of exposing the full catalog for every request, an application can first identify a relevant subset and make those tools available when needed. This can reduce unnecessary catalog exposure, but introduces a discovery step that must itself retrieve an appropriate set.

Use semantic search to shortlist candidates

A semantic-search layer can match a task to likely tools and present a smaller candidate set. AWS guidance also describes this pattern. Its quality depends on the descriptions, retrieval method, and task; it should be evaluated against real requests rather than assumed to work for every catalog.

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What to measure before calling it a 90-tool limit

  • Protocol pagination: Does the server return pages, and does the client follow the cursors?
  • Client behavior: Does the host or SDK impose an aggregation cap or cache results? What happens when the catalog changes?
  • Catalog exposure: Are all tools registered for every request, or are they filtered or retrieved when needed?
  • Selection accuracy: For the actual descriptions and tasks, does the model choose the intended tool?
  • Reproducibility: Can the issue be tied to a specific server, client, SDK version, authorization context, and number of pages or tools?

Without those details, “the catalog breaks at 90” is too vague to diagnose and should not be treated as a claim about MCP itself.

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