geonames-mcp-server

GeoNames reference vocabulary

geonames_list_reference

Read-onlyIdempotent

Decode GeoNames vocabulary used by the other tools: topic feature_classes lists the 9 one-letter classes; topic feature_codes lists the 684 feature codes with names and definitions, filterable by class and text; topic postal_countries lists the 122 countries with postal-code data and each one's code range and count. feature_classes and feature_codes are bundled and spend no credits; postal_countries costs 1 GeoNames credit a day (cached).

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "topic": "<topic>"
    },
    "name": "geonames_list_reference"
  }
}

Input Schema

Name	Required	Description
`limit`	No	Maximum entries to return, 1 to 1,000. This tool returns at most 700 per call: a larger limit is held to 700, and the notice says so when more entries remain. Default 100.
`topic`	Yes	Vocabulary to list: feature_classes (the 9 one-letter classes), feature_codes (the 684 codes), or postal_countries (countries with postal-code data).
`offset`	No	Entries to skip before the first one returned, for paging. Default 0.
`featureClass`	No	Topic feature_codes only: keep the codes of this one-letter class (A, H, L, P, R, S, T, U, V).
`nameContains`	No	Keep only entries whose code, name, or description contains every word of this text as a substring (port also matches airport), ignoring case, accents, and punctuation. Give at least one letter or digit.
`geonamesUsername`	No	Topic postal_countries only, and only when the list is not already cached: your own GeoNames username, so the call spends that account's credit instead of the server's. The account needs free web services enabled on its geonames.org account page.

Output Schema

Name	Required	Description
`cap`	No	The limit applied: limit as given, or 700 when it asked for more.
`error`	No	Present when the call failed. Absent on success.
`shown`	No	Entries returned on this page.
`topic`	No	The topic listed.
`notice`	No	Guidance when nothing matched, the offset is past the end, or more pages remain (naming a limit held to 700).
`entries`	No	Entries on this page, in GeoNames order.
`truncated`	No	True when more entries remain past this page.
`nextOffset`	No	Offset of the next page; absent on the last page.
`totalCount`	No	Entries matching the topic and filters, before paging.

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedOct 29, 2026

changedInput schema / properties / nameContains / description

Previous value: -"Keep only entries whose code, name, or description contains every word of this text as a substring (port also matches airport), ignoring case, accents, and punctuation."New value: +"Keep only entries whose code, name, or description contains every word of this text as a substring (port also matches airport), ignoring case, accents, and punctuation. Give at least one letter or digit."

changedOutput schema / properties / error / properties / data / properties / reason / description

Previous value: -"Machine-readable failure mode. Declared by this tool: `filter_not_applicable`: featureClass was given with a topic other than feature_codes. `username_required`: Neither geonamesUsername nor the server's GEONAMES_USERNAME supplies a GeoNames account. `caller_account_rejected`: GeoNames rejected the caller-supplied geonamesUsername (unknown user, or free web services not enabled). `server_account_rejected`: GeoNames rejected the server's GEONAMES_USERNAME. `quota_exhausted`: GeoNames reported the account's hourly, daily, or weekly credit limit spent, or this server's pacer for the account shed the call. `upstream_rejected_parameter`: GeoNames rejected a value the schema let through; the message carries its text. Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `filter_not_applicable`: featureClass was given with a topic other than feature_codes. `name_contains_unsearchable`: nameContains is not blank but holds no letter or digit (only punctuation, symbols, emoji, or invisible characters), so it would match every entry. `username_required`: Neither geonamesUsername nor the server's GEONAMES_USERNAME supplies a GeoNames account. `caller_account_rejected`: GeoNames rejected the caller-supplied geonamesUsername (unknown user, or free web services not enabled). `server_account_rejected`: GeoNames rejected the server's GEONAMES_USERNAME. `quota_exhausted`: GeoNames reported the account's hourly, daily, or weekly credit limit spent, or this server's pacer for the account shed the call. `upstream_rejected_parameter`: GeoNames rejected a value the schema let through; the message carries its text. Other values are possible when a failure originates below the handler."

changedOutput schema / properties / error / properties / data / properties / reason / examples

Previous value: -[
-  "filter_not_applicable",
-  "username_required",
-  "caller_account_rejected",
-  "server_account_rejected",
-  "quota_exhausted",
-  "upstream_rejected_parameter"
-]New value: +[
+  "filter_not_applicable",
+  "name_contains_unsearchable",
+  "username_required",
+  "caller_account_rejected",
+  "server_account_rejected",
+  "quota_exhausted",
+  "upstream_rejected_parameter"
+]

Changed6 schema fields changedOct 18, 2026

changedInput schema / properties / featureClass / description

Previous value: -"Topic feature_codes only: keep the codes of this one-letter class (A, H, L, P, R, S, T, U, V). Case-insensitive."New value: +"Topic feature_codes only: keep the codes of this one-letter class (A, H, L, P, R, S, T, U, V)."

changedInput schema / properties / limit / description

Previous value: -"Maximum entries to return, 1 to 700. Default 100."New value: +"Maximum entries to return, 1 to 1,000. This tool returns at most 700 per call: a larger limit is held to 700, and the notice says so when more entries remain. Default 100."

changedInput schema / properties / limit / maximum
```
Previous value: -700New value: +1000
```

changedInput schema / properties / topic / description

Previous value: -"Vocabulary to list: feature_classes (the 9 one-letter classes), feature_codes (the 684 codes), or postal_countries (countries with postal-code data). Case-insensitive."New value: +"Vocabulary to list: feature_classes (the 9 one-letter classes), feature_codes (the 684 codes), or postal_countries (countries with postal-code data)."

changedOutput schema / properties / cap / description

Previous value: -"The limit that was applied."New value: +"The limit applied: limit as given, or 700 when it asked for more."

changedOutput schema / properties / notice / description

Previous value: -"Guidance when nothing matched, the offset is past the end, or more pages remain."New value: +"Guidance when nothing matched, the offset is past the end, or more pages remain (naming a limit held to 700)."

First observedOct 2, 2026

TDQS

A4.1/5.0

Behavior4/5

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

Annotations already declare readOnly/idempotent/openWorld, so the key added value here is cost disclosure: feature_classes and feature_codes are bundled and free, postal_countries costs 1 credit/day and is cached. That is exactly the kind of behavior an agent needs before calling. It does not discuss pagination behavior or result shape beyond counts, so not a 5.

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 the purpose, then the three topics, then the cost terms — a sensible order with no filler. Slightly run-on as one dense sentence, but every clause (topic contents, filtering, credits, caching) carries information.

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?

Output schema exists and the parameter schema is fully documented, so the description only needs to carry purpose and cost, which it does. Minor gaps remain: it doesn't mention the 700-entry per-call cap or paging behavior, leaving those to the schema.

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% and both enums plus every parameter are already documented in the schema. The description adds only light mapping ("filterable by class and text", "each one's code range and count"), which the schema largely covers already. Baseline 3 applies when the schema does the heavy lifting.

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 (decode) and resource (GeoNames vocabulary) and enumerates the three topics with exact contents: 9 classes, 684 codes, 122 postal countries. An agent can distinguish this from the place-lookup siblings (geonames_search_places, geonames_get_place, etc.) without opening any schema.

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 phrase "vocabulary used by the other tools" makes clear this is the supporting reference tool, and the option-by-option breakdown implies which topic to pick. It stops short of explicit when/when-not guidance or naming a sibling alternative, so it is clear context rather than routing rules.

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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