list_marksUse this when choosing or configuring chart mark types. Returns every available mark with its properties and defaults.
| Name | Required | Description | Default |
|---|---|---|---|
No arguments | |||
| Name | Required | Description | Default |
|---|---|---|---|
| marks | Yes | ||
| shared | Yes |
Changes observed during successful MCP inspections.
Output schema / properties / marks / items / properties / type / enumAdded value: +[
+ "dot",
+ "line",
+ "barY",
+ "barX",
+ "areaY",
+ "areaX",
+ "pie",
+ "text",
+ "ruleX",
+ "ruleY"
+]Output schema / (root)Previous value: -nullNew value: +{
+ "$schema": "http://json-schema.org/draft-07/schema#",
+ "additionalProperties": false,
+ "properties": {
+ "marks": {
+ "items": {
+ "additionalProperties": false,
+ "properties": {
+ "description": {
+ "type": "string"
+ },
+ "specific": {
+ "additionalProperties": {
+ "type": "string"
+ },
+ "propertyNames": {
+ "type": "string"
+ },
+ "type": "object"
+ },
+ "type": {
+ "type": "string"
+ }
+ },
+ "required": [
+ "type",
+ "description",
+ "specific"
+ ],
+ "type": "object"
+ },
+ "type": "array"
+ },
+ "shared": {
+ "additionalProperties": {
+ "type": "string"
+ },
+ "propertyNames": {
+ "type": "string"
+ },
+ "type": "object"
+ }
+ },
+ "required": [
+ "shared",
+ "marks"
+ ],
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and destructiveHint=false. The description adds that the tool returns properties and defaults, providing useful behavioral context beyond annotations. No contradiction.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences, front-loaded with usage guidance, then return description. Every word earns its place; no waste.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given that an output schema exists (not shown but indicated), the description does not need to detail return values. It covers when to use and what the tool returns, which is complete for a simple list tool with good annotations and schema.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
The schema has 0 parameters, so schema coverage is 100%. The description does not need to explain parameters. Baseline 4 applies.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description uses a specific verb ('Returns') and resource ('mark types') and clearly distinguishes from sibling tools (none of which deal with mark types). It states both the use case and the output.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
Explicitly says 'Use this when choosing or configuring chart mark types', which tells the agent when to invoke it. No mention of when not to use or alternatives, but the context from siblings makes it sufficient.
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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