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 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.
`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 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.

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 cover the read-only, idempotent, open-world profile, yet the description adds genuinely non-obvious behavior: two topics spend no credits, postal_countries costs one credit per day, and results are cached. It also implies the geonamesUsername path avoids server credit spend. Missing is any note on truncation/paging limits, which live only in the schema.

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?

One densely packed sentence with the purpose front-loaded and three semicolon-separated clauses, one per topic, so nothing is wasted. It is a single long sentence with no explicit structure or line breaks, which slightly harms scannability.

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 six parameters, a full output schema and annotations present, the description covers what an agent needs: what each topic yields, which are free, which costs a credit, and that results are cached. The only gap is paging behavior when results exceed the 700-per-call cap, which is left entirely 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 description coverage is 100%, so the parameters are already fully self-documenting and 3 is the baseline. The description corroborates that feature_codes is filterable by class and text and that postal_countries returns code range and count, but names no parameter and adds no semantics the schema lacks.

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 and resource ('Decode GeoNames vocabulary') and then enumerates all three topics with concrete contents (9 one-letter classes, 684 codes with names and definitions, 122 postal countries with code ranges). Relative to siblings like geonames_search_places or geonames_reverse_geocode, it is unmistakably a static reference-lookup tool rather than a query tool.

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?

'Vocabulary used by the other tools' gives a clear context for when to reach for it, and the cost split tells the agent which topic is free versus paid. It stops short of explicit exclusions (e.g., 'do not use this to look up a place') or an ordered workflow such as resolving feature codes before calling search.

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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