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).

Input Schema

TableJSON Schema

Name	Required	Description
`limit`	No	Maximum entries to return, 1 to 700. 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). Case-insensitive.
`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). Case-insensitive.
`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.
`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

TableJSON Schema

Name	Required	Description
`cap`	No	The limit that was applied.
`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.
`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.

First observedOct 2, 2026

TDQS

A4.5/5.0

Behavior5/5

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

Annotations already cover read-only/idempotent/open-world, and the description goes well beyond them: it discloses that feature_classes and feature_codes spend no credits while postal_countries costs 1 credit/day and is cached, plus that geonamesUsername spends the caller's own credit and requires free web services enabled. That is exactly the cost/caching behavior an agent needs before invoking.

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?

Three tight sentences, purpose front-loaded, with the free-vs-credit distinction placed last. Every clause earns its place, though the topic enumeration is somewhat dense.

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?

An output schema exists so return shapes need no explanation, and the description covers all three topics plus their cost and caching semantics. A brief word on how filters interact across topics (e.g., nameContains applying to postal_countries too) is the only minor gap.

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?

Schema coverage is 100%, so the baseline is 3; the description still adds value by tying filters to topics (feature_codes filterable by class and text) and by pairing each topic with its data size, which helps an agent reason about pagination via limit/offset.

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... vocabulary') and resource, then enumerates exactly the three topics it can return with their sizes (9 classes, 684 codes, 122 countries). This clearly distinguishes it from sibling place-lookup tools like geonames_search_places or geonames_get_place.

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?

'Decode GeoNames vocabulary used by the other tools' frames the use case — it is a lookup of vocabulary needed to interpret the other tools' outputs — and the per-topic credit note tells the agent which topic is cheap. It does not explicitly state when-not to use it, but the context is clear.

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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