congressgov-mcp-server

Congress.gov Roll Votes

congressgov_roll_votes

Read-onlyIdempotent

Retrieve U.S. congressional roll call votes and individual member voting positions for either chamber. Set 'chamber' to 'house' (default, from the Congress.gov API) or 'senate' (from the Senate's official LIS feed). Use 'list' to find votes by congress and session (newest first by default), 'get' for vote details (question, result, tallies, party breakdown, associated bill/nomination/amendment), or 'members' for how each member voted.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`limit`	No	Results per page (1-250).
`order`	No	Sort order for 'list'. 'recent' (default) returns newest first; 'oldest' returns ascending. House sorts by vote update date (with 'recent', offset=0 always returns the strictly newest page); Senate sorts by roll call number. Ignored by 'get' and 'members'.	recent
`offset`	No	Pagination offset.
`chamber`	No	Chamber whose votes to query. 'house' (default) draws from the Congress.gov API; 'senate' draws from the Senate's official LIS roll-call feed. Roll call numbers reset each session and are specific to one chamber.	house
`session`	Yes	Session number (1 or 2). Odd years are session 1, even years session 2.
`congress`	Yes	Congress number.
`operation`	Yes	Which data to retrieve.
`voteNumber`	No	Roll call vote number. Required for 'get' and 'members'.

Output Schema

TableJSON Schema

Name	Required	Description
`data`	No	Result rows. Per-tool item shape is rendered in the markdown body.
`vote`	No	Dynamic upstream JSON record.
`error`	No	Present when the call failed. Absent on success.
`notice`	No	Guidance when results are empty, a page is past the end, or a caveat applies.
`pagination`	No	Pagination metadata: total count and next offset.
`totalCount`	No	Total results across all pages.
`effectiveQuery`	No	The browse scope and applied filters.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedAug 30, 2026

addedOutput schema / properties / vote

Added value: +{
+  "additionalProperties": {},
+  "description": "Dynamic upstream JSON record.",
+  "properties": {},
+  "type": "object"
+}

Changed6 schema fields changedAug 25, 2026

changedInput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

addedInput schema / additionalProperties
```
Added value: +false
```

changedOutput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

addedOutput schema / anyOf

Added value: +[
+  {
+    "not": {
+      "required": [
+        "error"
+      ]
+    },
+    "required": [
+      "effectiveQuery",
+      "totalCount"
+    ]
+  },
+  {
+    "required": [
+      "error"
+    ]
+  }
+]

addedOutput schema / properties / error

Added value: +{
+  "additionalProperties": {},
+  "description": "Present when the call failed. Absent on success.",
+  "properties": {
+    "code": {
+      "description": "JSON-RPC error code for this failure.",
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "data": {
+      "additionalProperties": {},
+      "properties": {
+        "reason": {
+          "description": "Machine-readable failure mode. Declared by this tool: `not_found`: A requested bill, member, committee, report, vote, or nomination does not exist in Congress.gov. `rate_limited`: The Congress.gov API rate limit (5,000 requests/hour per key) was exceeded. `invalid_request`: Congress.gov rejected the request as malformed — a bad date range or an identifier with an unexpected shape. `upstream_error`: Congress.gov returned an unexpected error (5xx or another non-2xx status). Other values are possible when a failure originates below the handler.",
+          "examples": [
+            "not_found",
+            "rate_limited",
+            "invalid_request",
+            "upstream_error"
+          ],
+          "type": "string"
+        },
+        "recovery": {
+          "additionalProperties": {},
+          "description": "Actionable next step for the caller.",
+          "properties": {
+            "hint": {
+              "type": "string"
+            }
+          },
+          "required": [
+            "hint"
+          ],
+          "type": "object"
+        },
+        "retryable": {
+          "description": "Whether retrying may succeed.",
+          "type": "boolean"
+        }
+      },
+      "type": "object"
+    },
+    "message": {
+      "description": "Human-readable description of what went wrong.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "code",
+    "message"
+  ],
+  "type": "object"
+}

removedOutput schema / required

Removed value: -[
-  "effectiveQuery",
-  "totalCount"
-]

Changed2 schema fields changedJun 2, 2026

addedInput schema / properties / chamber

Added value: +{
+  "default": "house",
+  "description": "Chamber whose votes to query. 'house' (default) draws from the Congress.gov API; 'senate' draws from the Senate's official LIS roll-call feed. Roll call numbers reset each session and are specific to one chamber.",
+  "enum": [
+    "house",
+    "senate"
+  ],
+  "type": "string"
+}

changedInput schema / properties / order / description

Previous value: -"Sort order for 'list', by vote update date. 'recent' (default) returns newest first; 'oldest' returns ascending. With 'recent', offset=0 always returns the strictly newest page. Ignored by 'get' and 'members'."New value: +"Sort order for 'list'. 'recent' (default) returns newest first; 'oldest' returns ascending. House sorts by vote update date (with 'recent', offset=0 always returns the strictly newest page); Senate sorts by roll call number. Ignored by 'get' and 'members'."

Changed6 schema fields changedMay 30, 2026

removedOutput schema / description

Removed value: -"Detail-mode key 'vote' carries: Vote record for `get` and `members` (question, result, party totals, member positions); absent for `list`."

addedOutput schema / properties / effectiveQuery

Added value: +{
+  "description": "The browse scope and applied filters.",
+  "type": "string"
+}

addedOutput schema / properties / notice

Added value: +{
+  "description": "Guidance when results are empty, a page is past the end, or a caveat applies.",
+  "type": "string"
+}

removedOutput schema / properties / query

Removed value: -{
-  "description": "Echo of the applied filters for list-mode queries. Rendered as the first line of the response.",
-  "type": "string"
-}

addedOutput schema / properties / totalCount

Added value: +{
+  "description": "Total results across all pages.",
+  "type": "number"
+}

addedOutput schema / required

Added value: +[
+  "effectiveQuery",
+  "totalCount"
+]

Changed5 schema fields changedMay 21, 2026

changedInput schema / properties / order / description

Previous value: -"Sort order for 'list' (sorts by update date). 'recent' (default) is newest first; 'oldest' is ascending. The upstream API ignores sort params on this endpoint, so 'recent' is implemented client-side by fetching the tail and reversing. Ignored by 'get' and 'members'."New value: +"Sort order for 'list', by vote update date. 'recent' (default) returns newest first; 'oldest' returns ascending. With 'recent', offset=0 always returns the strictly newest page. Ignored by 'get' and 'members'."

changedOutput schema / description

Previous value: -"Vote data from Congress.gov API."New value: +"Detail-mode key 'vote' carries: Vote record for `get` and `members` (question, result, party totals, member positions); absent for `list`."

addedOutput schema / properties / data

Added value: +{
+  "description": "Result rows. Per-tool item shape is rendered in the markdown body.",
+  "items": {
+    "additionalProperties": {},
+    "description": "Upstream JSON record. Per-tool item shape is rendered in the markdown body.",
+    "properties": {},
+    "type": "object"
+  },
+  "type": "array"
+}

addedOutput schema / properties / pagination

Added value: +{
+  "additionalProperties": false,
+  "description": "Pagination metadata: total count and next offset.",
+  "properties": {
+    "count": {
+      "description": "Total result count across all pages.",
+      "maximum": 9007199254740991,
+      "minimum": 0,
+      "type": "integer"
+    },
+    "nextOffset": {
+      "anyOf": [
+        {
+          "maximum": 9007199254740991,
+          "minimum": 0,
+          "type": "integer"
+        },
+        {
+          "type": "null"
+        }
+      ],
+      "description": "Offset to pass for the next page, or null when there are no more pages."
+    }
+  },
+  "required": [
+    "count"
+  ],
+  "type": "object"
+}

addedOutput schema / properties / query

Added value: +{
+  "description": "Echo of the applied filters for list-mode queries. Rendered as the first line of the response.",
+  "type": "string"
+}

Changed1 schema field changedMay 21, 2026

addedInput schema / properties / order

Added value: +{
+  "default": "recent",
+  "description": "Sort order for 'list' (sorts by update date). 'recent' (default) is newest first; 'oldest' is ascending. The upstream API ignores sort params on this endpoint, so 'recent' is implemented client-side by fetching the tail and reversing. Ignored by 'get' and 'members'.",
+  "enum": [
+    "recent",
+    "oldest"
+  ],
+  "type": "string"
+}

First observedMar 28, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, openWorldHint, and idempotentHint, so the safety profile is covered. The description adds meaningful behavioral context: house data comes from the Congress.gov API while senate data comes from the Senate's LIS feed, list returns newest first by default, and 'get' returns specific fields (question, result, tallies, party breakdown, associated bill/nomination/amendment). This goes beyond the annotations without contradicting 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?

The description is three sentences, front-loaded with the core purpose, and each sentence earns its place. It efficiently packs chamber sourcing, operation types, and return content without redundancy or filler. The structure is scannable and immediately actionable for an agent.

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?

The description covers operation semantics, chamber selection, data sources, and default ordering. The input schema documents all parameters, and an output schema exists, so return values are already specified. Minor gaps like pagination behavior are handled by the schema; overall, the agent has everything needed to select and invoke the tool correctly. A 4 is appropriate given the tool's complexity.

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%, so the baseline is 3. The description does not add much parameter-level meaning beyond the schema: it mentions operation-to-parameter mapping and the chamber data source, but the schema already documents voteNumber's requirement for 'get'/'members' and the chamber-specific roll call reset behavior. No significant param semantics are added beyond what the schema provides.

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?

The description opens with a specific verb-resource pair ('Retrieve U.S. congressional roll call votes and individual member voting positions') and immediately distinguishes the tool's domain from the sibling tools (bill lookup, committee reports, etc.). It further clarifies scope by chamber and by operation, leaving no ambiguity about what the tool does.

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

Usage Guidelines4/5

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

The description provides explicit operation selection guidance: 'Use 'list'...', 'get' for vote details..., or 'members' for how each member voted.' It also distinguishes data sources for house vs senate. It does not explicitly state when not to use this tool versus a sibling, but the sibling tools are clearly different domains, so exclusion guidance is unnecessary.

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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