categoryFetch all coins belonging to a CoinMarketCap category (e.g. DeFi, NFTs) by category id (obtain ids from the categories tool); returns price, market cap, and 24h change per coin.
| Name | Required | Description | Default |
|---|---|---|---|
| id | Yes | Category id (from `categories`) | |
| convert | No |
| Name | Required | Description | Default |
|---|---|---|---|
| data | No | ||
| status | No |
Changes observed during successful MCP inspections.
Input schema / examplesAdded value: +[
+ {
+ "id": "defi"
+ },
+ {
+ "convert": "EUR",
+ "id": "layer-1"
+ }
+]Output schema / (root)Previous value: -nullNew value: +{
+ "properties": {
+ "data": {
+ "properties": {
+ "avg_price_change": {
+ "description": "Average price change percentage",
+ "type": "number"
+ },
+ "cryptocurrencies": {
+ "description": "Cryptocurrencies in this category",
+ "items": {
+ "type": "object"
+ },
+ "type": "array"
+ },
+ "description": {
+ "description": "Category description",
+ "type": "string"
+ },
+ "id": {
+ "description": "Category ID",
+ "type": "string"
+ },
+ "last_updated": {
+ "description": "Last update ISO timestamp",
+ "type": "string"
+ },
+ "market_cap": {
+ "description": "Total market cap of category",
+ "type": "number"
+ },
+ "market_cap_change": {
+ "description": "Market cap change percentage",
+ "type": "number"
+ },
+ "name": {
+ "description": "Category name",
+ "type": "string"
+ },
+ "num_tokens": {
+ "description": "Number of cryptocurrencies in category",
+ "type": "integer"
+ },
+ "title": {
+ "description": "Category title",
+ "type": "string"
+ },
+ "volume_24h": {
+ "description": "24-hour trading volume",
+ "type": "number"
+ }
+ },
+ "type": "object"
+ },
+ "status": {
+ "properties": {
+ "credit_count": {
+ "description": "API credits consumed",
+ "type": "integer"
+ },
+ "elapsed": {
+ "description": "Elapsed milliseconds",
+ "type": "integer"
+ },
+ "error_code": {
+ "description": "Error code (0 for success)",
+ "type": "integer"
+ },
+ "error_message": {
+ "description": "Error message if applicable",
+ "type": [
+ "string",
+ "null"
+ ]
+ },
+ "timestamp": {
+ "description": "ISO timestamp",
+ "type": "string"
+ }
+ },
+ "type": "object"
+ }
+ },
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint, covering the safety profile. The description adds value by detailing the return output (price, market cap, 24h change per coin), which goes beyond annotations.
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?
The description is a single, well-structured sentence that front-loads the action and outcome without any superfluous words.
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 the presence of an output schema and annotations, the description adequately covers the tool's purpose and return values. It does not discuss pagination or ordering, but for a simple fetch with two params, this is sufficient.
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 description explains the required 'id' parameter (obtained from 'categories') but does not elaborate on the optional 'convert' parameter. With 50% schema coverage, the description partially compensates but could clarify 'convert' (likely a currency conversion, like 'EUR' in example).
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 clearly states it fetches coins belonging to a CoinMarketCap category, specifies the return fields (price, market cap, 24h change), and distinguishes from the sibling 'categories' tool by referencing it for obtaining IDs.
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?
The description explicitly guides the user to obtain IDs from the 'categories' tool, which is a clear prerequisite. However, it does not provide explicit exclusions or alternative use cases, which is acceptable for a focused fetch tool.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Add one secure layer between your agents and this server.