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[MCP] Prevent duplicating entities between custom tools and describe_entities #3076

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[MCP] Prevent duplicating entities between custom tools and describe_entities #3076

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0a4c986
[MCP] Prevent duplicating tool list between custom tools and describe…
souvikghosh04 Jan 22, 2026
e701a87
Minor fixes and refactoring
souvikghosh04 Jan 22, 2026
c793712
Copilot review fixes
souvikghosh04 Jan 22, 2026
b9fd106
Copilot review fixes
souvikghosh04 Jan 22, 2026
e2cc3e8
Fix behavior of dmltools and custom tools combinations
souvikghosh04 Jan 22, 2026
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31 changes: 31 additions & 0 deletions src/Azure.DataApiBuilder.Mcp/BuiltInTools/DescribeEntitiesTool.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -146,6 +146,10 @@ public Task<CallToolResult> ExecuteAsync(

List<Dictionary<string, object?>> entityList = new();

// Track how many stored procedures were filtered out because they're exposed as custom-tool-only.
// This helps provide a more specific error message when all entities are filtered.
int filteredCustomToolCount = 0;

if (runtimeConfig.Entities != null)
{
foreach (KeyValuePair<string, Entity> entityEntry in runtimeConfig.Entities)
Expand All @@ -155,6 +159,18 @@ public Task<CallToolResult> ExecuteAsync(
string entityName = entityEntry.Key;
Entity entity = entityEntry.Value;

// Filter out stored procedures when dml-tools is explicitly disabled (false).
// This applies regardless of custom-tool setting:
// - custom-tool: true, dml-tools: false → Filtered (appears only in tools/list)
// - custom-tool: false, dml-tools: false → Filtered (entity fully disabled for MCP)
// When dml-tools is true (or default), the entity appears in describe_entities.
if (entity.Source.Type == EntitySourceType.StoredProcedure &&
entity.Mcp?.DmlToolEnabled == false)
{
filteredCustomToolCount++;
continue;
}

if (!ShouldIncludeEntity(entityName, entityFilter))
{
continue;
Expand All @@ -177,6 +193,7 @@ public Task<CallToolResult> ExecuteAsync(

if (entityList.Count == 0)
{
// No entities matched the filter criteria
if (entityFilter != null && entityFilter.Count > 0)
{
return Task.FromResult(McpResponseBuilder.BuildErrorResult(
Expand All @@ -185,6 +202,20 @@ public Task<CallToolResult> ExecuteAsync(
$"No entities found matching the filter: {string.Join(", ", entityFilter)}",
logger));
}
// All entities were filtered because they're custom-tool-only - only return this specific error
// if ALL configured entities were filtered (not just some). This prevents misleading errors
// when entities fail to build for other reasons (e.g., exceptions in Build*EntityInfo).
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@RubenCerna2079 RubenCerna2079 Jan 29, 2026

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nit:

Suggested change
// when entities fail to build for other reasons (e.g., exceptions in Build*EntityInfo).
// when entities fail to build for other reasons (e.g., exceptions in Build*EntityInfo functions).

else if (filteredCustomToolCount > 0 &&
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@RubenCerna2079 RubenCerna2079 Jan 29, 2026

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Wouldn't we also want a situation where only some of the entities were filtered?

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@RubenCerna2079 RubenCerna2079 Jan 29, 2026

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Just saw its purpose is to show the user when all their tools are custom-tools, although it might be a good idea to also give the user the information that their SPs that are custom-tools are in a different place.

runtimeConfig.Entities != null &&
filteredCustomToolCount == runtimeConfig.Entities.Entities.Count)
{
return Task.FromResult(McpResponseBuilder.BuildErrorResult(
toolName,
"AllEntitiesFilteredAsCustomTools",
$"All {filteredCustomToolCount} configured entities are stored procedures exposed as custom-tool-only (dml-tools: false). Custom tools appear in tools/list, not describe_entities. Use the tools/list endpoint to discover available custom tools.",
logger));
}
// Truly no entities configured in the runtime config, or entities failed to build for other reasons
else
{
return Task.FromResult(McpResponseBuilder.BuildErrorResult(
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