.model_context_windows. must be greater than 0

Error message

{name}.model_context_windows.{model} must be greater than 0

What it means

Per-model context window overrides in a provider's `model_context_windows` table must be greater than zero. A zero entry would produce a zero token budget for that model, so validation rejects it. Thrown by validate_model_context_windows at config.rs:4090.

Solutions

Set the model's window to its real positive limit.
Delete the zero entry so the model falls back to the provider-level context_window or default.
Fix the generator/lookup that emitted 0 for unknown models.

Example fix

// before
model_context_windows = { "claude-x" = 0 }
// after
model_context_windows = { "claude-x" = 200000 }

Defensive patterns

Strategy: validation

Validate before calling

for (model, w) in provider.model_context_windows.iter().flatten() {
    if *w == 0 { return Err(format!("{model} context window must be > 0")); }
}

Prevention

Remove unknown-model entries instead of filling them with 0.
Validate generated per-model tables before writing config.

When it happens

Trigger: A provider's `model_context_windows` BTreeMap contains a model whose value is exactly 0, e.g. model_context_windows = { "gpt-4o" = 0 }. The error names the offending provider and model.

Common situations: Placeholder zeros left in generated config; overriding a model whose limit was unknown and someone wrote 0; scripted config generation where a fetch returned 0.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

AI-assisted analysis of Hmbown/CodeWhale@73e0f67d83 (2026-09-22). Data as JSON: /api/errors/806bfb3b0e854b05. Report an issue: GitHub.

Appendix: source

Thrown at crates/tui/src/config.rs:4090

        Ok(())
    }
}

fn validate_provider_context_window(name: &str, value: Option<u32>) -> Result<()> {
    if value == Some(0) {
        anyhow::bail!("{name}.context_window must be greater than 0");
    }
    Ok(())
}

fn validate_model_context_windows(
    name: &str,
    table: Option<&std::collections::BTreeMap<String, u32>>,
) -> Result<()> {
    if let Some(table) = table {
        for (model, window) in table {
            if *window == 0 {
                anyhow::bail!("{name}.model_context_windows.{model} must be greater than 0");
            }
        }
    }
    Ok(())
}

#[derive(Debug, Clone, Deserialize, Default)]
struct ConfigFile {
    /// Boxed so the parsed document never carries the multi-kilobyte
    /// `Config` by value through `toml::de` and `apply_profile` frames. A
    /// `#[tokio::test]` runs those frames on libtest's default 2 MiB stack,
    /// which the by-value copies overflowed (#6362).
    #[serde(flatten)]
    base: Box<Config>,
    profiles: Option<HashMap<String, Config>>,
}

#[derive(Debug, Clone, Deserialize, Default)]

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