# What Is LCOV? — The lcov.info Tracefile Format, Line by Line

Canonical: https://commareports.com/glossary/lcov
Published: 2026-10-23

> LCOV is the plain-text coverage format behind lcov.info: SF, DA, BRDA, FN and end_of_record. What each record means, which tools write it, and how to read one without genhtml.

# LCOV

**LCOV is a plain-text code coverage format: a tracefile (usually
`lcov.info`) that lists each source file followed by one record per
line, branch and function with how many times it ran.** It is named after
`lcov`, the front-end to GCC's `gcov`, but today it is the format almost
every coverage tool can write and almost every coverage service can read.

## What is in a file

```text
TN:
SF:src/cart/cart.ts
FN:15,applyCoupon
FNDA:9,applyCoupon
FNF:1
FNH:1
DA:15,9
DA:16,9
DA:20,7
DA:21,0
LF:4
LH:3
BRDA:20,0,0,0
BRDA:20,0,1,7
BRF:2
BRH:1
end_of_record
```

| Record                                    | Meaning                                                    |
| ----------------------------------------- | ---------------------------------------------------------- |
| `TN:<name>`                               | Test name — often empty; several runs can be concatenated  |
| `SF:<path>`                               | Starts a source file (usually an absolute path)            |
| `FN:<line>,<name>`                        | A function declared at that line (LCOV 2 adds an end line) |
| `FNDA:<hits>,<name>`                      | How many times that function was called                    |
| `DA:<line>,<hits>`                        | An executable line and its hit count                       |
| `BRDA:<line>,<block>,<branch>,<taken>`    | One side of a branch; `-` means the condition never ran    |
| `LF` / `LH`, `BRF` / `BRH`, `FNF` / `FNH` | Lines, branches, functions found / hit                     |
| `end_of_record`                           | Closes the file                                            |

Line coverage is `LH / LF`; branch coverage is `BRH / BRF`.

## Who writes it

- **C and C++:** `lcov --capture` over gcov data, or `llvm-cov export -format=lcov`
- **JavaScript and TypeScript:** Istanbul/nyc, c8, Jest and Vitest with the
  `lcov` reporter, Bun (`--coverage-reporter=lcov`), Deno (`deno coverage --lcov`)
- **Python:** `coverage lcov` (coverage.py 6.3+)
- **Rust:** `cargo llvm-cov --lcov`, grcov
- **Dart and Flutter:** `flutter test --coverage` writes `coverage/lcov.info`
- **Go:** `go test -coverprofile` plus `gcov2lcov`

Codecov, Coveralls, SonarQube and the coverage gutters in VS Code and JetBrains all read it.

## The parts that bite

- **Absolute paths.** `SF:` usually holds the CI runner's path
  (`/home/runner/work/app/app/src/…`), so tools that match files against
  the repository need a path rewrite or `--base-directory`.
- **Summaries can disagree with records.** `LF`/`LH` are written by the
  tool, not checked by the reader. When tracefiles are concatenated or
  edited, recount from the `DA` lines.
- **Merging is a sum.** The same `SF:` in two runs should be added
  together (`lcov --add-tracefile`), so a line hit by either suite counts
  as covered — appending files without merging double-lists them.
- **No statements.** LCOV has lines, branches and functions. Istanbul's
  "statements" percentage does not survive the conversion, which is why
  numbers drift between tools.

## Reading one without genhtml

`genhtml coverage.info -o out` turns a tracefile into a browsable HTML tree,
but it needs Perl and the lcov package. The free
[coverage viewer](/tools/coverage-viewer) reads `lcov.info` (and Cobertura
or Clover XML) in the browser: line, branch and function coverage, a
roll-up per directory, files sorted least-covered first with their
uncovered line ranges, and a Markdown summary for the pull request.

## Try it

Comma is free — unlimited reports, unlimited commenters, unlimited
revision history.

**[Open the coverage viewer →](/tools/coverage-viewer)**

### Related

- [Cobertura](/glossary/cobertura) — the XML alternative GitLab and Azure DevOps read
- [Code coverage](/glossary/code-coverage) — line, branch, statement, and what a percentage hides
- [Share an lcov / genhtml report](/share-lcov-report) · [Share a coverage report](/share-coverage-report)
- [JUnit XML](/glossary/junit-xml) · [Coverage report links 404](/fix/coverage-report-links-broken) · [Glossary](/glossary)