languagetool-org/languagetool · error · IllegalArgumentException

Invalid value for maxTextCheckerThreads, must be >= 1:

Error message

Invalid value for maxTextCheckerThreads, must be >= 1: 

What it means

maxTextCheckerThreads (added as a per-text checker pool, default 0 = inherit maxCheckThreads) must be >= 0; the message text says '>= 1' but the code enforces >= 0. Values below 0 throw this IllegalArgumentException.

Source

Thrown at languagetool-server/src/main/java/org/languagetool/server/HTTPServerConfig.java:369

          ruleIdToConfidenceFile = new File(ruleIdToConfidence);
        }
        String langModel = getOptionalProperty(props, "languageModel", null);
        if (langModel != null && loadLangModel) {
          setLanguageModelDirectory(langModel);
        }
        String fasttextModel = getOptionalProperty(props, "fasttextModel", null);
        String fasttextBinary = getOptionalProperty(props, "fasttextBinary", null);
        if (fasttextBinary != null && fasttextModel != null) {
          setFasttextPaths(fasttextModel, fasttextBinary);
        }
        maxCheckThreads = Integer.parseInt(getOptionalProperty(props, "maxCheckThreads", "10"));
        if (maxCheckThreads < 1) {
          throw new IllegalArgumentException("Invalid value for maxCheckThreads, must be >= 1: " + maxCheckThreads);
        }
        // default value 0 = use maxCheckThreads setting (for compatibility)
        maxTextCheckerThreads = Integer.parseInt(getOptionalProperty(props, "maxTextCheckerThreads", "0"));
        if (maxTextCheckerThreads < 0) {
          throw new IllegalArgumentException("Invalid value for maxTextCheckerThreads, must be >= 1: " + maxTextCheckerThreads);
        }
        textCheckerQueueSize = Integer.parseInt(getOptionalProperty(props, "textCheckerQueueSize", "8"));
        if (textCheckerQueueSize < 0) {
          throw new IllegalArgumentException("Invalid value for textCheckerQueueSize, must be >= 1: " + textCheckerQueueSize);
        }

        boolean atdMode = getOptionalProperty(props, "mode", "LanguageTool").equalsIgnoreCase("AfterTheDeadline");
        if (atdMode) {
          throw new IllegalArgumentException("The AfterTheDeadline mode is not supported anymore in LanguageTool 3.8 or later");
        }
        String rulesConfigFilePath = getOptionalProperty(props, "rulesFile", null);
        if (rulesConfigFilePath != null) {
          rulesConfigFile = new File(rulesConfigFilePath);
          if (!rulesConfigFile.exists() || !rulesConfigFile.isFile()) {
            throw new RuntimeException("Rules Configuration file cannot be found: " + rulesConfigFile);
          }
        }
        String remoteRulesConfigFilePath = getOptionalProperty(props, "remoteRulesFile", null);

View on GitHub (pinned to 2e990059ce)

Solutions

1. Set maxTextCheckerThreads to 0 (use maxCheckThreads) or a positive integer
2. Remove the property to keep the default behavior
3. Fix any config generator emitting negative values

Example fix

# before
maxTextCheckerThreads=-1
# after
maxTextCheckerThreads=0

int t = Integer.parseInt(props.getProperty("maxTextCheckerThreads", "0"));
if (t < 0) throw new IllegalArgumentException("maxTextCheckerThreads must be >= 0 (0 = use maxCheckThreads), got " + t);

try { cfg = new HTTPServerConfig(props, args); } catch (IllegalArgumentException e) {
  if (e.getMessage().contains("maxTextCheckerThreads")) { props.setProperty("maxTextCheckerThreads", "0"); cfg = new HTTPServerConfig(props, args); } else throw e;
}

When it happens

Trigger: Setting 'maxTextCheckerThreads' to a negative integer (e.g. -5) in the properties file.

Common situations: Config typos with minus signs; copying validation guidance ('must be >= 1') and assuming 0 is invalid — 0 is actually the documented default meaning 'use maxCheckThreads'.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• Invalid value for maxCheckThreads, must be >= 1:
• maxWorkQueueSize must be >= 0:
• Invalid value for textCheckerQueueSize, must be >= 1:
• No rules are active. Please make sure your rule ids (<option
• suppressMisspelledMatch must be a valid regex

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/79bfaa127b361f6a. Report an issue: GitHub.