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get_template_instances

Find concrete instantiations of a C/C++ template across all translation units, each with its full type signature, to resolve specializations that text search misses.

Instructions

Find all template instantiations for a C/C++ class or function template — libclang template-aware lookup. Finds concrete instantiations spread across all translation units, each with its full type signature. Text-based search cannot resolve template specializations across translation units.

Returns concrete instantiations of the template — each with its full type signature (e.g. Callback<void(int)>). The template declaration itself is also returned as the first result when found.

Uses the template_usr column populated during indexing via libclang's cursor.specialized_template.

Known limitation: libclang's specialized_template does not reliably resolve implicit instantiations or template methods of template classes. Header-only templates (e.g. RingBuffer<T>) may report zero instances even when used in the codebase. Explicit specializations and class/struct instantiations are detected more reliably than method-level instantiations.

For finding the template declaration itself use lookup_symbol.

Read-only. No side effects.

Args: template_name: Template name to find instantiations for. E.g. 'Callback' or 'mbed::Callback'. project_root: Project root. Auto-detected if omitted. project: Project name or project_id — call list_projects to get them. Use it to ask about a project that is not the project of the current directory. It is an alternative to project_root, which takes a root path. Give one of the two, not both. limit: Maximum results (default 50, max 200). variant: Build variant (multi-build project). Omit to use default_variant. One query answers for ONE build. image: Sysbuild image within the variant. Required when the variant holds several: each image is a separate program.

Returns: list[dict] with one element wrapping the template declaration: {name, qualified_name, kind, file, line, is_definition, signature, instances (list of dicts, each with name, qualified_name, kind, file, line, signature, is_definition), instance_count (int)}

No match gives ``[]``.  One dict with ``error`` means the query
failed — check that key first.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
imageNoSysbuild image within the variant. Required when the variant holds several: each image is a separate program.
limitNoMaximum results (default 50, max 200).
projectNoProject name or project_id — call list_projects to get them. Use it to ask about a project that is not the project of the current directory. It is an alternative to project_root, which takes a root path. Give one of the two, not both.
variantNoBuild variant (multi-build project). Omit to use default_variant. One query answers for ONE build.
project_rootNoProject root. Auto-detected if omitted. This field also accepts a project name or a project_id, but project is the clear field for those.
template_nameYesTemplate name to find instantiations for. E.g. 'Callback' or 'mbed::Callback'.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
resultYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed5 schema fields changedv0.32.0
    • changedInput schema / properties / image / description
      Previous value: -"Sysbuild image name within the variant (multi-project). Omit for all images of the variant."New value: +"Sysbuild image within the variant. Required when the variant holds several: each image is a separate program."
    • changedInput schema / properties / limit / description
      Previous value: -"Maximum results (default 50)."New value: +"Maximum results (default 50, max 200)."
    • addedInput schema / properties / limit / minimum
      Added value: +1
    • addedInput schema / properties / template_name / minLength
      Added value: +1
    • changedInput schema / properties / variant / description
      Previous value: -"Build variant name (multi-project). Omit to use default_variant or fail-closed. Use '*' for all variants."New value: +"Build variant (multi-build project). Omit to use default_variant. One query answers for ONE build."
  2. Changed3 schema fields changedv0.30.0
    • addedInput schema / additionalProperties
      Added value: +false
    • addedInput schema / properties / project
      Added value: +{
+  "anyOf": [
+    {
+      "type": "string"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null,
+  "description": "Project name or project_id — call list_projects to get them. Use it to ask about a project that is not the project of the current directory. It is an alternative to project_root, which takes a root path. Give one of the two, not both.",
+  "title": "Project"
+}
    • changedInput schema / properties / project_root / description
      Previous value: -"Project root. Auto-detected if omitted."New value: +"Project root. Auto-detected if omitted. This field also accepts a project name or a project_id, but project is the clear field for those."
  3. Changed2 schema fields changedv0.25.3
    • addedInput schema / properties / image
      Added value: +{
+  "anyOf": [
+    {
+      "type": "string"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null,
+  "description": "Sysbuild image name within the variant (multi-project). Omit for all images of the variant.",
+  "title": "Image"
+}
    • addedInput schema / properties / variant
      Added value: +{
+  "anyOf": [
+    {
+      "type": "string"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null,
+  "description": "Build variant name (multi-project). Omit to use default_variant or fail-closed. Use '*' for all variants.",
+  "title": "Variant"
+}
  4. Addedv0.7.0

TDQS

A4.9/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description fully carries the burden. It declares read-only behavior, no side effects, explains the internal mechanism (template_usr column, cursor.specialized_template), discloses reliability limitations for implicit instantiations, and specifies return behavior for no-match and error cases. No contradictions with annotations since none exist.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Well-structured and front-loaded: the purpose is stated first, then returns, limitations, and parameters. Despite length, every sentence adds essential information—no fluff. Sections are clearly separated, making it easy to scan.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity (6 params, 1 required, no annotations), the description is exceptionally complete. It covers parameter semantics, return format (with example signature), failure modes, limitations, and alternatives. Nothing an agent needs to call it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so baseline is 3. The description adds value by giving concrete examples for template_name, clarifying the project_root vs. project relationship ('Give one of the two, not both'), explaining limit defaults and max, variant's single-build behavior, and image's requirement. This exceeds the schema by providing usage context.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Find all template instantiations for a C/C++ class or function template') and distinguishes itself from text-based search and from lookup_symbol for finding the declaration. The purpose is unambiguous and clearly differentiates from sibling tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly provides when to use (template-aware lookup for cross-TU specialization resolution) and when not to (for the declaration itself, use lookup_symbol). It also states the limitation that header-only templates may yield zero results, giving the agent a clear decision framework.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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