Lexicon MCP

Lexicon MCP is a local-first multilingual dictionary, thesaurus, translation, lexical-relations, semantic-neighbour, and English wordplay server for the Model Context Protocol (MCP). It serves a versioned corpus from disk and performs no network access or data mutation while running.

Model-visible tools

The server exposes exactly six tools:

1. dictionary_lookup

2. dictionary_synonyms

3. dictionary_translate

4. dictionary_relations

5. dictionary_semantic_neighbors

6. dictionary_wordplay

Dataset installation, verification, repair, and rollback are deliberately CLI-only.

Related MCP server: FilePilot AI

Local development

Requirements: Python 3.13 and uv.

uv sync --extra dev
uv run pytest
uv run ruff check .

Run the MCP server after installing a verified dataset:

$env:LEXICON_DATA_DIR = 'E:\AI\data\lexicon-mcp'
uv run --frozen lexicon-mcp

The server never downloads data. If no verified corpus is active, it exits with a diagnostic containing the exact lexicon-data install command.

Dataset lifecycle

lexicon-data install --profile full --version data-v1.0.0
lexicon-data status
lexicon-data verify
lexicon-data repair
lexicon-data rollback

LEXICON_DATA_DIR selects the installation root. Releases are immutable and the active dataset is selected through an atomically replaced current.json pointer. Downloads resume into .partial files, are hash-checked before extraction, and are activated only after database/index integrity checks.

Corpus

The full build combines independently attributed snapshots of:

• Open English WordNet 2025 for English synsets and lexical relations;

• the English Wiktionary Wiktextract/Kaikki raw dump for multilingual entries, senses, examples, pronunciation, etymology, and translations;

• ConceptNet 5.7 for multilingual lexical and commonsense relations;

• ConceptNet Numberbatch 19.08 for multilingual semantic neighbours; and

• CMUdict for English pronunciation and wordplay.

Every public result identifies its source, dataset version, language, sense scope, and license. ConceptNet-only results are explicitly unsensed.

Data builds and releases

sources.lock.json freezes exact source revisions and hashes. The build pipeline is streaming and checkpointed; it does not build the unused Google n-gram database from the earlier community project. Data artifacts are packaged into independently hashed parts below 1 GiB and published under a separate immutable data-v* release.

Code and data releases are intentionally separate:

• code: v1.0.0

• data: data-v1.0.0

The code release pins an exact compatible data release and never resolves latest.

Prior art

This is an independent clean-room implementation. The project idea was informed by Eyalm321/multilingual-dictionary-mcp, which is acknowledged as prior art. No source code or Git history was copied.

Security and privacy

• Runtime databases are opened read-only and query-only.

• SQL uses bound parameters; query text is never interpreted as SQL.

• Tool inputs and result counts are bounded.

• Runtime operation is fully offline.

• Dataset administration is never exposed to the model.