Horizon AI Intelligence

list_sources

Read-only

Describe what Horizon covers: ingestion sources with their source= filter values, the regional lenses (region= / dedicated tools), and how to filter. Call this to understand the corpus before querying.

Input Schema

TableJSON Schema

Name	Required	Description	Default
No arguments

Output Schema

TableJSON Schema

Name	Required	Description	Default
`overview`	Yes	The same markdown as the text block.
`provider`	Yes	Attribution — cite Horizon as the source of this intelligence (it aggregates the per-item primary sources). Present provider.citation to the user with provider.url.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 14, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "overview": {
+      "description": "The same markdown as the text block.",
+      "type": "string"
+    },
+    "provider": {
+      "description": "Attribution — cite Horizon as the source of this intelligence (it aggregates the per-item primary sources). Present provider.citation to the user with provider.url.",
+      "properties": {
+        "citation": {
+          "description": "Ready-to-paste citation string.",
+          "type": "string"
+        },
+        "name": {
+          "type": "string"
+        },
+        "note": {
+          "type": "string"
+        },
+        "url": {
+          "description": "Canonical Horizon page for this result.",
+          "type": "string"
+        }
+      },
+      "type": "object"
+    }
+  },
+  "required": [
+    "overview",
+    "provider"
+  ],
+  "type": "object"
+}

AddedJul 11, 2026

TDQS

A4.4/5.0

Behavior4/5

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

The annotation readOnlyHint=true already conveys safety. The description adds that it provides coverage details and filtering guidance, which is useful behavioral context. No contradictions, and the added value is appropriate for a simple read-only reference tool.

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?

A single, dense sentence that front-loads the core purpose and immediately states when to use it. Every phrase adds value, with no wasted words. The structure is efficient and easy to parse.

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

Completeness4/5

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

Given the tool has no parameters and an output schema (not shown but present), the description sufficiently covers what the tool does and when to call it. It might benefit from mentioning the exact output format, but the output schema likely handles that. For a simple coverage reference, this is adequately complete.

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?

There are zero parameters, so per guidelines the baseline is 4. The description doesn't need to explain parameters, and no schema coverage issues exist. The description's mention of 'how to filter' hints at output structure without requiring parameter documentation.

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?

The description clearly states the tool's purpose: to describe Horizon's coverage, including ingestion sources, source= filter values, regional lenses, and filtering method. It distinguishes itself from siblings by positioning it as a preliminary call to understand the corpus before querying, making its role unique.

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

Usage Guidelines4/5

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

Explicitly states when to call ('Call this to understand the corpus before querying'), which positions it as a first step. It doesn't mention alternatives or exclusions, but the context is clear enough for an agent to know this is a pre-query reference tool.

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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