MCP Saved-Query Tools

Saved-query tools are JSON-defined, parameterized queries scoped to a collection. They appear as first-class MCP tools alongside core tools like query_collection — AI agents pick them by name, pass arguments, and receive filtered, formatted results. No PHP is needed; the definition lives in the collection’s schema editor.

Use saved-query tools when a particular query is reused or when you want to give an AI agent a stable, named entry point. For ad-hoc filter composition, query_collection is the better choice.

Quick start

Open the schema editor for the collection you want to expose. On the MCP tab, find the Custom MCP Tools field — it renders as a deck of tool rows. Click Add and fill in the id, description, filters, etc. Behind the scenes the deck stores tools keyed by their id:

{
  "featured_posts": {
    "id": "featured_posts",
    "description": "Return featured blog posts, newest first.",
    "filters": {
      "featured": { "value": true }
    },
    "sort":  "date:desc",
    "limit": 10
  }
}

The deck key matches the tool’s id — that’s the canonical identifier; the inner id field is what you enter in the form. Save the schema. The tool featured_posts is live on /mcp immediately — no rebuild, no restart.

Tool definition reference

Each tool entry is an object with the following fields. Only id and description are required.

Field	Required	Type	Notes
id	yes	string	Snake_case ^[a-z][a-z0-9_]*$. Becomes the wire-level tool name when registered. The registered name (base + any mcp.toolPrefix) must be ≤ 64 characters; the save-time validator enforces the full limit. Globally unique across all tools.
description	yes	string	Min 1, max 1024 characters. Describe what the tool returns — not how an agent should use it.
params	no	object	Typed caller parameters (see Parameterized tools). Omit for fixed-filter tools.
filters	no	object	Field-name → {value, operator?} map. Filter values may reference {{params.X}} placeholders.
sort	no	string	REST-style sort spec, e.g. date:desc or priority:asc,date:desc.
limit	no	integer	Max results per call. Default 20, capped at 50.
offset	no	integer	Skip the first N matching results. Default 0.
include	no	string	REST-style include filter — escape hatch for filter shapes the filters object can’t express.
exclude	no	string	REST-style exclude filter — escape hatch.
format	no	enum	Output format for rich-text fields: markdown (default), html, or text.

The mcp-tool.json JSON Schema enforces maxLength: 64 on the base id field only — it cannot dynamically account for the site’s configured mcp.toolPrefix. The save-time validator performs the full prefix-inclusive check: strlen(toolPrefix + "_" + id) ≤ 64. If a site has a 10-character prefix configured, base ids must be ≤ 54 characters. The error message will state both the prefix in use and the resulting length.

Fixed-filter tools

Fixed-filter tools take no caller arguments. They are preset queries with a stable result shape — useful for “give me all draft posts” or “return the three most recent announcements”:

{
  "draft_posts": {
    "id": "draft_posts",
    "description": "Return blog posts pending editorial review, oldest first.",
    "filters": {
      "status": { "value": "draft" }
    },
    "sort":  "date:asc",
    "limit": 20
  },
  "recent_announcements": {
    "id": "recent_announcements",
    "description": "The three most recent site announcements.",
    "sort":  "date:desc",
    "limit": 3
  }
}

Parameterized tools

Add a params block to accept caller-supplied arguments. Reference them in filter values with {{params.X}} placeholders.

{
  "id": "find_listings_by_city",
  "description": "Search active real-estate listings by city and optional maximum price.",
  "params": {
    "city": {
      "type": "string",
      "description": "City name (case-insensitive substring match).",
      "required": true
    },
    "max_price": {
      "type": "number",
      "description": "Maximum listing price in USD.",
      "minimum": 0
    }
  },
  "filters": {
    "status": { "value": "active" },
    "city":   { "operator": "contains", "value": "{{params.city}}" },
    "price":  { "operator": "lte",      "value": "{{params.max_price}}" }
  },
  "sort":  "price:asc",
  "limit": 20
}

How placeholders work

• {{params.X}} is the only recognized placeholder syntax. Other {{...}} strings in filter values are treated as literals.
• When a placeholder replaces the entire filter value (e.g. "value": "{{params.city}}"), the resolved value is type-coerced to match the param’s declared type.
• When a placeholder is embedded in a longer string (e.g. "value": "category-{{params.slug}}"), the resolved segment is cast to string and the parts are concatenated.
• If an optional param is not supplied by the caller, the filter containing its placeholder is excluded from the query. The tool still runs against the remaining filters.

Param properties

Property	Required	Type	Notes
type	yes	enum	string, number, integer, boolean
description	no	string	Shown to AI agents in the generated inputSchema
required	no	boolean	Default false. Required params are enforced by the SDK before dispatch.
default	no	any	Default value used when the param is absent
enum	no	array	Restrict to a specific set of values
minimum	no	number	Numeric lower bound
maximum	no	number	Numeric upper bound
format	no	string	JSON Schema format hint (e.g. date, uri)

Param names must match ^[a-z][a-z0-9_]*$.

Filter operators

Specify an operator alongside value in any filter entry. The default is eq.

Operator	Meaning
eq	Equal (default)
ne	Not equal
lt	Less than
lte	Less than or equal
gt	Greater than
gte	Greater than or equal
contains	Substring match (case-insensitive for string fields)
starts	Starts with
ends	Ends with
in	Value is in a pipe-separated list (a|b|c)
notin	Value is not in a pipe-separated list

"filters": {
  "tag":    { "operator": "contains", "value": "featured" },
  "rating": { "operator": "gte",      "value": 4 },
  "status": { "operator": "notin",    "value": "draft|archived" }
}

Persona inheritance and safety

A saved-query tool inherits its access level from the parent collection’s MCP Access setting (admin or public). There is no per-tool override.

When the public persona calls the tool, T3’s standard safety filters run after the tool’s filters: draft objects are excluded, and fields marked expose: false in the collection’s MCP field settings are stripped from every response. Saved-query tools cannot bypass these filters.

Tool name collisions

Collision detection runs at two points:

Save-time (warning, non-blocking). When you save the schema, each tool name is checked against currently registered core and extension tools. A collision triggers a warning banner in the admin — it does not block the save. The colliding tool will be silently skipped from tools/list at runtime until the name is changed.

Server-build-time (strict deny). When the MCP server initializes, SchemaToolRegistrar walks all collections. If the same tool name appears in two different collections, both tools are dropped from tools/list. Core and extension tools always win over schema tools. Rename one of the conflicting tools to resolve the issue.

If a tool is missing from tools/list despite being defined in the schema, check the admin’s warnings UI for collision notices and review the application log for entries from SchemaToolRegistrar.

Saved-query tools vs query_collection

	Saved-query tool	query_collection
Definition	JSON in schema editor	Called ad-hoc by AI agent
Agent selects by	Tool name	Tool name + inline args
Best for	Stable, reused queries	Ad-hoc filter composition
Caller can change filters	No (fixed + declared params only)	Yes
Requires PHP	No	No

Use a saved-query tool when you want a predictable, named entry point. Use query_collection when the agent needs to compose filters freely.

Common pitfalls

Tool id format. Only lowercase letters, digits, and underscores. Must start with a letter. Max 64 characters including any mcp.toolPrefix the operator has configured.

Total tool count. Most MCP clients degrade in usability above roughly 50 tools. If you define many saved-query tools across multiple collections, watch the cumulative count in the admin’s MCP status panel.

{{params.X}} is the only placeholder syntax. Filter values containing other {{...}} strings are passed through as literals. Future macro syntax will use a different prefix.

Referencing an undeclared param. If a filter value contains {{params.X}} but X is not declared in the params block, the tool fails at runtime with a validation error. The admin’s warnings UI will surface the issue on next save.

Do not write LLM instructions into the description. “Always call this tool first” reads as prompt injection at directory review. Lead with what the tool returns.

Reference

• MCP Server — personas, transport, core tool catalog, collection MCP settings.
• Extending MCP — registering tools and resources from PHP extensions, progress notifications, error handling, persona-aware handlers.