openaq-mcp-server

openaq-mcp-server: list parameters

openaq_list_parameters

Read-onlyIdempotent

Catalog of every measurable pollutant and its canonical unit: id, code, display name, unit, and a one-line description (pm25, pm10, o3, no2, so2, co, bc, and more). This is the unit-disambiguation reference — the same pollutant exists under several ids with different units (CO is id 4 in µg/m³, id 8 in ppm, id 102 in ppb), so use this to pick the exact parametersId for openaq_find_locations / openaq_get_readings / openaq_get_measurements and to interpret a reading's unit. A small bounded catalog fetched live from OpenAQ.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`query`	No	Case-insensitive filter over the bounded parameter catalog by code, display name, and description (e.g. "pm" for particulates, "ozone", "co"). Omit to list everything.
`pollutantsOnly`	No	When true, exclude meteorological/auxiliary parameters (temperature, humidity, wind, pressure, particle-count channels) and return only air pollutants. Default false (full catalog).

Output Schema

TableJSON Schema

Name	Required	Description
`error`	No	Present when the call failed. Absent on success.
`notice`	No	Guidance when the query matched nothing.
`parameters`	No	Matching parameters. Multiple rows can share a name with different ids/units — pick the id whose unit you want.
`totalCount`	No	Total parameters matched after filtering.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 24, 2026

changedInput schema / properties / query / description

Previous value: -"Case-insensitive filter over the bounded parameter catalog (~44) by code, display name, and description (e.g. \"pm\" for particulates, \"ozone\", \"co\"). Omit to list everything."New value: +"Case-insensitive filter over the bounded parameter catalog by code, display name, and description (e.g. \"pm\" for particulates, \"ozone\", \"co\"). Omit to list everything."

Changed4 schema fields changedSep 20, 2026
- removedOutput schema / properties / parameters / items / properties / description / anyOf
```
Removed value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]
```
- addedOutput schema / properties / parameters / items / properties / description / type
```
Added value: +[
+  "string",
+  "null"
+]
```
- removedOutput schema / properties / parameters / items / properties / displayName / anyOf
```
Removed value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]
```
- addedOutput schema / properties / parameters / items / properties / displayName / type
```
Added value: +[
+  "string",
+  "null"
+]
```

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": [
+      "parameters",
+      "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: `upstream_error`: OpenAQ /parameters returned 5xx or an unreadable body on every retry. `rate_limited`: OpenAQ returned 429 — the request budget for this key is exhausted. `upstream_timeout`: OpenAQ /parameters did not respond within the request timeout on every retry. `invalid_api_key`: OpenAQ returned 401 — the configured OPENAQ_API_KEY is missing, invalid, or revoked. Other values are possible when a failure originates below the handler.",
+          "examples": [
+            "upstream_error",
+            "rate_limited",
+            "upstream_timeout",
+            "invalid_api_key"
+          ],
+          "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: -[
-  "parameters",
-  "totalCount"
-]

Changed1 schema field changedJul 1, 2026

changedInput schema / properties / query / description

Previous value: -"Local case-insensitive filter on code, display name, and description (e.g. \"pm\" for particulates, \"ozone\", \"co\"). The full catalog is small (~44 entries); omit to list everything. This filters the fetched list on our side — it is not an upstream search."New value: +"Case-insensitive filter over the bounded parameter catalog (~44) by code, display name, and description (e.g. \"pm\" for particulates, \"ozone\", \"co\"). Omit to list everything."

First observedJun 16, 2026

TDQS

A4.5/5.0

Behavior4/5

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

Annotations already declare readOnlyHint and idempotentHint, so safety is covered. The description adds genuine behavioral context beyond that: the catalog is bounded, fetched live from OpenAQ, and contains multiple ids for the same pollutant with different units. It stops short of mentioning rate limits or expected catalog size, hence 4 rather than 5.

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 dense but every sentence earns its place: scope, fields, canonical-unit pitfall with concrete examples, downstream usage, and live-fetch behavior. It is front-loaded with 'Catalog of every measurable pollutant and its canonical unit' and wastes no words.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present, return values need not be explained in the description. The description covers what the catalog contains, why it matters, when to call it, and the live/bounded nature of the data, which is complete for an optional-parameter, read-only list tool.

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 schema already fully documents the query and pollutantsOnly parameters. The tool description adds useful conceptual framing (unit disambiguation) but does not itself explain the parameters, so it stays at the baseline 3 without adding extra parameter-level meaning.

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 states a specific verb and resource: listing the parameter catalog, with concrete fields (id, code, display name, unit, description). It also differentiates the tool from siblings by positioning it as the unit-disambiguation reference rather than a data-reading or location tool.

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?

Explicitly tells the agent when to use it: to pick the exact parametersId for openaq_find_locations, openaq_get_readings, and openaq_get_measurements, and to interpret a reading's unit. It names the downstream tools and the decision this tool supports, making the invocation context unmistakable.

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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