logdigest

Condense a log file to its failure evidence.

A CI or test log can run to ten thousand lines, but the part anyone reads is the handful of failure sections: the failing test, the error line, the stack, the nonzero exit. logdigest reads a log file, finds those lines, groups them into sections with their original line numbers, and prints a digest you can read in one screen. It reports a verdict of FAILURES-FOUND when it finds any failure section and NO-FAILURES when it finds none.

Install

npx @reneturcios/logdigest digest build.log

Or install it globally:

npm install -g @reneturcios/logdigest

Requires Node 20 or newer.

Related MCP server: log-essence

CLI

logdigest digest [file] [--json]
logdigest mcp
logdigest --version

• logdigest digest <file> prints the human readable digest.

• logdigest digest <file> --json prints the full report as JSON.

• logdigest mcp runs the MCP server over stdio (see below).

• logdigest --version prints the version.

Exit codes: 0 when the verdict is NO-FAILURES, 1 when the verdict is FAILURES-FOUND, 2 for a usage or read error (for example, the target is a directory or cannot be read), and 141 when the reader closed the output pipe early.

Example digest:

logdigest digest test.log: FAILURES-FOUND
  2 failure section(s) found in 28 line(s): 9 matched line(s).
  [HIGH] TEST-FAIL lines 5-16
FAIL src/math.test.ts
    AssertionError: expected 3 to be 4
        at Object.<anonymous> (src/math.test.ts:10:11)
  totals: total lines 28, matched lines 9, sections 2, overflow sections 0
  by rule: TEST-FAIL 8, ERROR-LINE 1, EXIT-NONZERO 0

(The example above is shortened; the real digest prints every captured line of every section.)

MCP

The same binary is an MCP server:

npx @reneturcios/logdigest mcp

It exposes one tool:

• digest_log with a path argument (the log file to check). It returns the same report as the CLI --json output.

What it detects

Detection is pattern based. Every matched line is assigned to exactly one rule; when a line matches several patterns, the most specific rule wins (TEST-FAIL over EXIT-NONZERO over ERROR-LINE).

How sections and verdicts work

• Matched lines that are within 3 lines of each other form one section. A wider gap starts a new section.

• After a stack head (a Traceback line, the first at stack line of a run, or a matched line directly followed by a stack line), up to 5 further lines are captured as context, so the top of a stack survives the digest. The capture never crosses into the next section.

• Each section becomes one finding. Its line is the section's first line number, its evidence is the first matched line, and findings also carry endLine and the captured sectionLines.

• Severity is high for a TEST-FAIL or ERROR-LINE section that contains a stack head or an assertion, and medium otherwise. An empty log produces one info finding with rule EMPTY-LOG.

• The report counts totalLines, matchedLines, sections (sections actually emitted), sectionsTotal, overflowSections, and one count per rule.

• Verdict: FAILURES-FOUND if there is at least one section, otherwise NO-FAILURES. An empty log is NO-FAILURES with the EMPTY-LOG finding above.

• Findings are capped at 200 sections. Sections past the cap are not emitted, but they are counted in overflowSections so the report never silently truncates.

• In the human readable digest, each section prints its line range followed by its captured lines verbatim, trimmed to 200 characters per line, then the totals. Output is deterministic: it is a pure function of the file contents, with no timestamps.

Limits

• Detection is pattern based, so a log that phrases a failure in a novel way, with none of the shapes in the table above, can be missed. A NO-FAILURES verdict means "no known failure shape was found", not a proof that the run succeeded.

• logdigest condenses; it does not diagnose. It surfaces the failure lines and their immediate context, but root cause analysis beyond the lines it surfaces is up to the reader.

• Only the first 200 sections are emitted (the rest are counted), and rendered lines are trimmed to 200 characters, so a digest is a starting point for reading the original log, not a copy of it. The original line numbers are always preserved so any section can be found in the source log.

Development

npm install
npm run build
npm test

The core is in src/core.ts and uses only the Node standard library.