Datacircle

List the APIs

list_apis

Read-onlyIdempotent

Lists the APIs on Datacircle's sheet and the number of plans and providers for each. Pass an API's name to search_plans. It takes no arguments and gives the whole sheet in one answer, every API in the sheet's order, with no paging: each API's name (api), how many plans (plans) and providers (providers) it has, its sheet (sheetPage) and, where it has one, its best page (bestPage), which ranks its providers on our benchmark. Call it first when you don't know an API's name; when you do, call search_plans with it straight away. Free, no key, read-only.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "list_apis"
  }
}

Input Schema

Name	Required	Description	Default
No arguments

Output Schema

Name	Required	Description	Default
`apis`	Yes	Every API on the sheet, in its order.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedNov 6, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "apis": {
+      "description": "Every API on the sheet, in its order.",
+      "items": {
+        "properties": {
+          "api": {
+            "description": "The API's name, the api search_plans takes.",
+            "type": "string"
+          },
+          "bestPage": {
+            "description": "The API's best page on datacircle.dev, which ranks its providers on our benchmark. Left out where it has none.",
+            "format": "uri",
+            "type": "string"
+          },
+          "plans": {
+            "description": "How many plans the API has on the sheet.",
+            "minimum": 1,
+            "type": "integer"
+          },
+          "providers": {
+            "description": "How many providers sell it.",
+            "minimum": 1,
+            "type": "integer"
+          },
+          "sheetPage": {
+            "description": "The API's sheet on datacircle.dev: its plans and their prices.",
+            "format": "uri",
+            "type": "string"
+          }
+        },
+        "required": [
+          "api",
+          "plans",
+          "providers"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    }
+  },
+  "required": [
+    "apis"
+  ],
+  "type": "object"
+}

First observedOct 20, 2026

TDQS

A4.5/5.0

Behavior4/5

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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world), yet the description adds non-obvious behavior: no arguments, no paging, whole-sheet return in sheet order, and the operational facts 'Free, no key'. Some of the field-level return detail duplicates the existing output schema, so it is not maximally additive, but the access and pagination facts are genuinely beyond the annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with what the tool returns and tightly packed with actionable facts. It runs slightly long and repeats the annotation in 'read-only', but no sentence is off-topic for selecting or calling the tool.

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?

For a zero-argument list tool with a full output schema and rich annotations, the description covers purpose, interop, pagination, and access requirements. The only inefficiency is re-enumerating return fields that the output schema already defines, so completeness is met but with overlapping content.

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?

With zero parameters the baseline is 4, and the description correctly reinforces 'It takes no arguments', which prevents an agent from guessing at filters. There is no parameter meaning to add beyond that.

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?

States a specific verb and resource ('Lists the APIs on Datacircle's sheet') plus exactly what each row contains (name, plans, providers, sheetPage, bestPage). It also distinguishes itself from the only sibling by naming search_plans and saying the API name is the handoff value.

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

Usage Guidelines5/5

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

Explicit routing rules: 'Call it first when you don't know an API's name; when you do, call search_plans with it straight away.' This states both the use case and the alternative, and the preceding 'Pass an API's name to search_plans' explains the interop.

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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