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fix: revert MAX_TOOL_NAME_LENGTH to 64 for Gemini compatibility

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The MCP spec recommends 128 characters, but Gemini enforces a 64-character
limit for function names. Since buildMcpToolName() is provider-agnostic
(called without provider context), we must use the lowest common denominator.

This ensures compatibility with all supported API providers.
This commit is contained in:
Roo Code 2026-01-16 14:30:45 +00:00
parent 7be724fdd1
commit ef21f947f2
2 changed files with 28 additions and 28 deletions
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46
src/utils/__tests__/mcp-name.spec.ts
View file

@ -33,7 +33,7 @@ describe("mcp-name utilities", () => {
})
it("should have correct max tool name length", () => {
expect(MAX_TOOL_NAME_LENGTH).toBe(128)
expect(MAX_TOOL_NAME_LENGTH).toBe(64)
})
it("should have correct hash suffix length", () => {
@ -165,24 +165,24 @@ describe("mcp-name utilities", () => {
expect(buildMcpToolName("server@name", "tool!name")).toBe("mcp--servername--toolname")
})
it("should truncate long names to 128 characters with hash suffix", () => {
const longServer = "a".repeat(80)
const longTool = "b".repeat(80)
it("should truncate long names to 64 characters with hash suffix", () => {
const longServer = "a".repeat(50)
const longTool = "b".repeat(50)
const result = buildMcpToolName(longServer, longTool)
expect(result.length).toBeLessThanOrEqual(128)
expect(result.length).toBe(128)
expect(result.length).toBeLessThanOrEqual(64)
expect(result.length).toBe(64)
expect(result.startsWith("mcp--")).toBe(true)
// Should end with underscore + 8 char hash suffix
expect(result).toMatch(/_[a-f0-9]{8}$/)
})
it("should use hash suffix for long names and cache them", () => {
const longServer = "a".repeat(80)
const longTool = "b".repeat(80)
const longServer = "a".repeat(50)
const longTool = "b".repeat(50)
const result = buildMcpToolName(longServer, longTool)
// The shortened name should be deterministic
expect(result.length).toBe(128)
expect(result.length).toBe(64)
expect(result).toMatch(/_[a-f0-9]{8}$/)
// Building again should return the same result (from cache)
@ -191,8 +191,8 @@ describe("mcp-name utilities", () => {
})
it("should produce deterministic hash suffixes", () => {
const longServer = "a".repeat(80)
const longTool = "b".repeat(80)
const longServer = "a".repeat(50)
const longTool = "b".repeat(50)
// Build the same name twice with cache cleared between
clearEncodedNameCache()
const result1 = buildMcpToolName(longServer, longTool)
@ -203,12 +203,12 @@ describe("mcp-name utilities", () => {
})
it("should produce unique hash suffixes for different tools", () => {
const longServer = "a".repeat(80)
const result1 = buildMcpToolName(longServer, "tool1_" + "x".repeat(70))
const result2 = buildMcpToolName(longServer, "tool2_" + "y".repeat(70))
const longServer = "a".repeat(50)
const result1 = buildMcpToolName(longServer, "tool1_" + "x".repeat(40))
const result2 = buildMcpToolName(longServer, "tool2_" + "y".repeat(40))
// Both should be truncated
expect(result1.length).toBe(128)
expect(result2.length).toBe(128)
expect(result1.length).toBe(64)
expect(result2.length).toBe(64)
// Should have different hash suffixes
expect(result1).not.toBe(result2)
})
@ -437,7 +437,7 @@ describe("mcp-name utilities", () => {
// Should NOT have hash suffix
expect(builtName).toBe("mcp--server--get___data")
expect(builtName.length).toBeLessThan(128)
expect(builtName.length).toBeLessThan(64)
// Normal decode path should work
const parsed = parseMcpToolName(builtName)
@ -456,7 +456,7 @@ describe("mcp-name utilities", () => {
const encodedName = buildMcpToolName(serverName, toolName)
// Should be truncated to 128 chars with hash suffix
expect(encodedName.length).toBe(128)
expect(encodedName.length).toBe(64)
expect(encodedName).toMatch(/_[a-f0-9]{8}$/)
// The new approach: use findToolByEncodedMcpName to find the matching tool
@ -487,8 +487,8 @@ describe("mcp-name utilities", () => {
})
it("should find tool for shortened names with hash suffix", () => {
const serverName = "a".repeat(80)
const toolName = "b".repeat(80) + "-hyphen"
const serverName = "a".repeat(50)
const toolName = "b".repeat(50) + "-hyphen"
const encodedName = buildMcpToolName(serverName, toolName)
// The encoded name should have a hash suffix
@ -541,8 +541,8 @@ describe("mcp-name utilities", () => {
describe("clearEncodedNameCache", () => {
it("should clear the encoded name cache", () => {
// Build some names to populate cache
const longServer = "a".repeat(80)
const longTool = "b".repeat(80)
const longServer = "a".repeat(50)
const longTool = "b".repeat(50)
buildMcpToolName(longServer, longTool)
buildMcpToolName("server", "tool")
@ -552,7 +552,7 @@ describe("mcp-name utilities", () => {
// Verify cache is cleared by checking that rebuilding takes the same path
// (we can't directly access the cache, but the function should work)
const result = buildMcpToolName(longServer, longTool)
expect(result.length).toBe(128)
expect(result.length).toBe(64)
expect(result).toMatch(/_[a-f0-9]{8}$/)
})
})

10
src/utils/mcp-name.ts
View file

@ -33,10 +33,10 @@ export const MCP_TOOL_PREFIX = "mcp"
export const HYPHEN_ENCODING = "___"
/**
* Maximum length for tool names (MCP spec limit).
* See: https://modelcontextprotocol.io/specification/2025-11-25/server/tools#tool-names
* Maximum length for tool names (Gemini's function name limit).
* * The MCP spec recommends 128, but Gemini enforces 64 characters.
*/
export const MAX_TOOL_NAME_LENGTH = 128
export const MAX_TOOL_NAME_LENGTH = 64
/**
* Length of hash suffix used when truncation is needed.
@ -192,7 +192,7 @@ export function sanitizeMcpName(name: string): string {
* Build a full MCP tool function name from server and tool names.
* The format is: mcp--{sanitized_server_name}--{sanitized_tool_name}
*
* The total length is capped at 128 characters per MCP spec.
* The total length is capped at 64 characters for Gemini compatibility.
* When truncation is needed, a hash suffix is appended to preserve uniqueness.
* The result is cached for efficient repeated lookups.
*
@ -224,7 +224,7 @@ export function buildMcpToolName(serverName: string, toolName: string): string {
// Format: truncated_name_HASHSUFFIX (underscore + 8 hex chars = 9 chars for suffix)
const hashSuffix = computeHashSuffix(serverName, toolName)
const suffixWithSeparator = `_${hashSuffix}` // "_" + 8 chars = 9 chars
const maxTruncatedLength = MAX_TOOL_NAME_LENGTH - suffixWithSeparator.length // 128 - 9 = 119
const maxTruncatedLength = MAX_TOOL_NAME_LENGTH - suffixWithSeparator.length // 64 - 9 = 55
// Truncate the full name and append hash suffix
const truncatedBase = fullName.slice(0, maxTruncatedLength)