ZEAM :: Prism

Sample the nodes for free

sample_rpc

Read-onlyIdempotent

Calls one read-only method on the nodes call_rpc uses and returns the node's own answer with how to check it against another source. Free, to check the nodes before you pay. No wallet. Eight read-only methods: eth_chainId, eth_blockNumber, eth_gasPrice, net_version, web3_clientVersion, net_peerCount, eth_syncing, txpool_status. For any other method, call_rpc. 60 calls an hour per network address, per tool. Example: {"chain":"base","method":"eth_blockNumber"}

Input Schema

Name	Required	Description	Default
`chain`	No	optional string — which node: eth or base. Default base.
`method`	No	optional string — one of eth_chainId, eth_blockNumber, eth_gasPrice, net_version, web3_clientVersion, net_peerCount, eth_syncing, txpool_status; default eth_blockNumber

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

Changed6 schema fields changedOct 15, 2026

removedInput schema / $schema

Removed value: -"https://json-schema.org/draft/2020-12/schema"

addedInput schema / examples

Added value: +[
+  {
+    "chain": "base",
+    "method": "eth_blockNumber"
+  }
+]

removedOutput schema / $schema

Removed value: -"https://json-schema.org/draft/2020-12/schema"

removedOutput schema / additionalProperties
```
Removed value: -{}
```

addedOutput schema / anyOf

Added value: +[
+  {
+    "properties": {
+      "chain": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "error": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "free_sample": {
+        "anyOf": [
+          {
+            "type": "boolean"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "http_status": {
+        "anyOf": [
+          {
+            "type": "number"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "method": {
+        "anyOf": [
+          {
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "paid_tool": {
+        "anyOf": [
+          {
+            "description": "the tool that does serve it",
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "refused": {
+        "anyOf": [
+          {
+            "description": "set when the method is outside the free sample",
+            "type": "boolean"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "rpc_response": {
+        "anyOf": [
+          {
+            "properties": {},
+            "type": "object"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "sample_methods": {
+        "anyOf": [
+          {
+            "description": "on a refusal: the methods the free sample serves",
+            "items": {
+              "type": "string"
+            },
+            "type": "array"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
+      "verify": {
+        "anyOf": [
+          {
+            "description": "how to check this answer against another source",
+            "type": "string"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      }
+    },
+    "type": "object"
+  },
+  {
+    "required": [
+      "error"
+    ],
+    "type": "object"
+  },
+  {
+    "required": [
+      "accepts"
+    ],
+    "type": "object"
+  },
+  {
+    "required": [
+      "receipt"
+    ],
+    "type": "object"
+  }
+]

removedOutput schema / properties

Removed value: -{
-  "chain": {
-    "type": [
-      "string",
-      "null"
-    ]
-  },
-  "error": {
-    "type": [
-      "string",
-      "null"
-    ]
-  },
-  "free_sample": {
-    "type": [
-      "boolean",
-      "null"
-    ]
-  },
-  "http_status": {
-    "type": [
-      "number",
-      "null"
-    ]
-  },
-  "method": {
-    "type": [
-      "string",
-      "null"
-    ]
-  },
-  "paid_tool": {
-    "anyOf": [
-      {
-        "description": "the tool that does serve it",
-        "type": "string"
-      },
-      {
-        "type": "null"
-      }
-    ]
-  },
-  "refused": {
-    "anyOf": [
-      {
-        "description": "set when the method is outside the free sample",
-        "type": "boolean"
-      },
-      {
-        "type": "null"
-      }
-    ]
-  },
-  "rpc_response": {
-    "anyOf": [
-      {
-        "additionalProperties": {},
-        "properties": {},
-        "type": "object"
-      },
-      {
-        "type": "null"
-      }
-    ]
-  },
-  "sample_methods": {
-    "anyOf": [
-      {
-        "description": "on a refusal: the methods the free sample serves",
-        "items": {
-          "type": "string"
-        },
-        "type": "array"
-      },
-      {
-        "type": "null"
-      }
-    ]
-  },
-  "verify": {
-    "anyOf": [
-      {
-        "description": "how to check this answer against another source",
-        "type": "string"
-      },
-      {
-        "type": "null"
-      }
-    ]
-  }
-}

Changed1 schema field changedOct 8, 2026

removedInput schema / properties / method / enum

Removed value: -[
-  "eth_chainId",
-  "eth_blockNumber",
-  "eth_gasPrice",
-  "net_version",
-  "web3_clientVersion",
-  "net_peerCount",
-  "eth_syncing",
-  "txpool_status"
-]

Changed2 schema fields changedOct 6, 2026

addedInput schema / properties / chain / enum
```
Added value: +[
+  "base",
+  "eth"
+]
```

addedInput schema / properties / method / enum

Added value: +[
+  "eth_chainId",
+  "eth_blockNumber",
+  "eth_gasPrice",
+  "net_version",
+  "web3_clientVersion",
+  "net_peerCount",
+  "eth_syncing",
+  "txpool_status"
+]

Changed1 schema field changedOct 5, 2026

addedOutput schema / properties / sample_methods

Added value: +{
+  "anyOf": [
+    {
+      "description": "on a refusal: the methods the free sample serves",
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    {
+      "type": "null"
+    }
+  ]
+}

Changed1 schema field changedOct 1, 2026

removedInput schema / properties / line

Removed value: -{
-  "description": "optional — your /pay credential: served off your line, not counted against the free ceiling; without it, or with a line that is off or out of time, free and counted.",
-  "type": "string"
-}

Changed1 schema field changedSep 18, 2026

changedInput schema / properties / line / description

Previous value: -"optional — your /pay credential: served off your line, not counted against the free ceiling; without it, free and counted."New value: +"optional — your /pay credential: served off your line, not counted against the free ceiling; without it, or with a line that is off or out of time, free and counted."

AddedSep 18, 2026

TDQS

A4.4/5.0

Behavior4/5

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

Annotations already declare read-only, idempotent, non-destructive, open-world. The description adds real behavioral context the annotations don't: no wallet required, free vs paid, and a rate limit of '60 calls an hour per network address, per tool.' It also tells the caller the response includes how to verify against another source. Docked slightly because it doesn't say what error/answer form an unsupported method or over-limit call returns.

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?

Front-loads the core action, then the free/no-wallet rationale, then the method enum, then the routing alternative, then rate limit, then a concrete example. Every sentence carries distinct information with no filler.

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?

With annotations and an output schema present, the description needn't explain return values, and it covers purpose, routing, cost model, and rate limits. Slightly incomplete on edge cases (behavior when rate-limited or when a non-listed method is passed) but otherwise sufficient to call it correctly.

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 coverage is 100%, so both parameters (chain enum and method list/defaults) are already fully documented in the schema. The description restates the eight methods and defaults from the schema, adding little beyond it; the example is useful but the schema already carries an example. Baseline 3 is appropriate.

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 (calls one read-only method) and resource (the nodes call_rpc uses), plus the distinctive free/read-only scope. It explicitly contrasts itself with the sibling call_rpc and enumerates the eight supported methods, so an agent can distinguish it without opening the schema.

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?

Says when to use this tool (free pre-check before paying, no wallet) and exactly when not to: 'For any other method, call_rpc.' The routing rule is explicit and pairs with the concrete conditional ('to check the nodes before you pay').

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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