check

Evaluate Lean code and collect all messages (errors, warnings, and info). Use this to check if code compiles without verification against a formal statement, or to get the output of #check / #eval statements.

Looking to confirm a proof? check reports compilation only — its okay field stays true even when a declaration uses sorry or a disallowed axiom. If you want a single pass/fail for "is this a complete, valid proof of a given statement," use verify_proof instead, which folds those failures into okay.

Input Parameters

content · str · required · Lean source code
The Lean source code to be processed by this tool.

mathlib_options · bool · default: False · Enable Mathlib options
If true, enables conventional Mathlib options. This toggle sets linter.mathlibStandardSet to true, autoImplicit to false, relaxedAutoImplicit to false, and pp.unicode.fun to true.

names · list[str] · Theorem names to process
Optional list of theorem names to process. If not specified, all theorems are processed.
Requesting a name not found in the code returns an error.
When theorems_only is false, these select over all declarations (not just theorems).

indices · list[int] · Theorem indices to process
Optional list of theorem indices to process (0-based). Supports negative indices:
-1 is the last theorem, -2 is second-to-last, etc.
If not specified, all theorems are processed.
When theorems_only is false, these select over all declarations (not just theorems).

theorems_only · bool · default: True · Process theorems/lemmas only
If true (default), only theorem/lemma declarations are processed. Set to false to process all declaration kinds (def/instance/abbrev/opaque/etc). When false, names and indices select over all declarations rather than just theorems.

ignore_imports · bool · default: True · Ignore import mismatches
Controls import statement handling:

• true (default): Ignore the imports in content and substitute the environment's default header. This uses the pre-built cached environment, so it is fast. The substituted code is returned in the content field.
• false: Process the imports in content exactly as written. This is significantly slower (the cached environment cannot be reused) and may produce inconsistent or incorrect results if a required dependency such as Mathlib.Tactic is missing. A warning is returned in these cases. See the troubleshooting page for more details.

environment · str · required · Lean environment or version
The Lean environment to use for evaluation. Each environment includes a specific Lean version and pre-built dependencies (typically Mathlib).

Available environments: lean-4.28.0, lean-4.27.0, lean-4.26.0, etc.

timeout_seconds · float · default: 120 · Max execution time in seconds
Maximum execution time in seconds. Requests exceeding this limit return a timeout error. Note that end-to-end request latency may exceed this timeout due to queue time and other overhead. Additionally, all non-admin requests are subject to an absolute maximum timeout of 900 seconds (15 minutes).

Output Fields

okay · bool · True if the Lean code compiles
Returns true if the code compiles without errors. Warnings don't affect this value.

This only reflects compilation. It does not mean the code is a complete, valid proof: a declaration that uses sorry, disallowed axioms, or unsafe definitions still compiles and leaves okay as true. Those findings are reported in tool_messages.warnings (with the offending names in failed_declarations). If you need to know whether the input is a real proof, also check that failed_declarations is empty, or better yet, use verify_proof.

content · string · Processed Lean code
The Lean code that was actually processed. May differ from input if ignore_imports=true caused header injection.

lean_messages · dict · Messages from Lean compiler
Messages from the Lean compiler with errors, warnings, and infos lists. Errors here indicate invalid Lean code (syntax errors, type errors, etc.); an empty errors list means the code compiles.

If the tool allows declaration selection and a names/indices selection is given, elaboration is skipped for the proofs of unselected declarations, so this field reflects only the selected declarations and is otherwise incomplete.

tool_messages · dict · Messages from check tool
Messages from the check tool with errors, warnings, and infos lists.

Validation findings — uses of sorry, disallowed axioms, or unsafe definitions — are reported as warnings here. Use verify_proof to treat them as errors.

failed_declarations · list · Declaration names that failed validation
List of declaration names that have compilation or validation errors. These are declarations that do not compile, use sorry, use disallowed axioms, etc. A file-level validation finding (e.g. use of open private) marks every declaration in the file as failed.

timings · dict · Execution timing breakdown
Timing information in milliseconds for various stages of processing.