Vizier

Catalogs

catalogs

Read-onlyIdempotent

Search VizieR catalogue metadata.

Input Schema

Name	Required	Description	Default
`max`	No	1-200 (default 25)
`query`	Yes	Keywords (e.g. "Gaia DR3", "exoplanet").

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedMay 22, 2026

addedInput schema / examples

Added value: +[
+  {
+    "query": "Gaia DR3"
+  },
+  {
+    "max": 50,
+    "query": "exoplanet"
+  }
+]

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "description": "VizieR catalogue metadata search results",
+  "oneOf": [
+    {
+      "additionalProperties": true,
+      "properties": {},
+      "type": "object"
+    },
+    {
+      "properties": {
+        "body": {
+          "description": "Raw text response (first 4000 chars)",
+          "type": "string"
+        },
+        "format": {
+          "description": "Format indicator when JSON parsing fails",
+          "enum": [
+            "raw"
+          ],
+          "type": "string"
+        }
+      },
+      "required": [
+        "format",
+        "body"
+      ],
+      "type": "object"
+    }
+  ],
+  "type": "object"
+}

First observedMay 18, 2026

TDQS

B3.3/5.0

Behavior3/5

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

Annotations already indicate readOnly, openWorld, idempotent, non-destructive. Description adds no behavioral context beyond annotations, but does not contradict them.

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?

Single sentence, front-loaded with key action. No wasted words.

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

Completeness3/5

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

Adequate for a simple search tool with good annotations and output schema. Could explain what VizieR is or how search works, but minimal is acceptable given tool simplicity.

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

Parameters3/5

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

Schema description coverage is 100% with clear descriptions for query and max. Description adds no extra meaning, meeting baseline for high coverage.

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

Purpose4/5

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

Description clearly states verb (Search) and resource (VizieR catalogue metadata), making purpose clear. However, it does not differentiate from sibling tools like query_catalog or cone_search, which also search catalogues.

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

Usage Guidelines2/5

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

No guidance on when to use this tool versus alternatives (e.g., cone_search, query_catalog) or what context is appropriate. Lacks any when/why information.

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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