Fuzz introspector
For issues and ideas: https://github.com/ossf/fuzz-introspector/issues
Project coverage

Table of contents

Project overview: tomlkit
High level conclusions
Reachability and coverage overview
Fuzzers overview
Project functions overview
Fuzzer details
Fuzzer: fuzz_dumps
Call tree
Fuzz blockers
Runtime coverage analysis
Files reached
Fuzzer: fuzz_parser
Call tree
Fuzz blockers
Runtime coverage analysis
Files reached
Analyses and suggestions
Optimal target analysis
Remaining optimal interesting functions
All functions overview
Fuzz engine guidance
/src/fuzz_dumps.py
Dictionary
Fuzzer function priority
/src/fuzz_parser.py
Dictionary
Fuzzer function priority
Runtime coverage analysis
Complex functions with low coverage
Files and Directories in report
Files in report
Directories in report
Metadata section
Report generation date: 2026-02-16

Project overview: tomlkit

High level conclusions

Reachability and coverage overview

Functions statically reachable by fuzzers
26.0%
100 / 382
Cyclomatic complexity statically reachable by fuzzers
31.0%
404 / 1314
Runtime code coverage of functions
61.0%
234 / 382

Warning: The number of runtime covered functions are larger than the number of reachable functions. This means that Fuzz Introspector found there are more functions covered at runtime than what is considered reachable based on the static analysis. This is a limitation in the analysis as anything covered at runtime is by definition reachable by the fuzzers.
This is likely due to a limitation in the static analysis. In this case, the count of functions covered at runtime is the true value, which means this is what should be considered "achieved" by the fuzzer.

Use the project functions table below to query all functions that were not covered at runtime.

Fuzzers overview

Fuzzer Fuzzer filename Functions Reached Functions unreached Fuzzer depth Files reached Basic blocks reached Cyclomatic complexity Details
fuzz_dumps /src/fuzz_dumps.py 98 567 6 6 42 303 fuzz_dumps.py
fuzz_parser /src/fuzz_parser.py 218 446 11 9 282 755 fuzz_parser.py

Project functions overview

The following table shows data about each function in the project. The functions included in this table correspond to all functions that exist in the executables of the fuzzers. As such, there may be functions that are from third-party libraries.

For further technical details on the meaning of columns in the below table, please see the Glossary .

Func name Functions filename Args Function call depth Reached by Fuzzers Runtime reached by Fuzzers Combined reached by Fuzzers Fuzzers runtime hit Func lines hit % I Count BB Count Cyclomatic complexity Functions reached Reached by functions Accumulated cyclomatic complexity Undiscovered complexity

Fuzzer details

Fuzzer: fuzz_dumps

Call tree

The calltree shows the control flow of the fuzzer. This is overlaid with coverage information to display how much of the potential code a fuzzer can reach is in fact covered at runtime. In the following there is a link to a detailed calltree visualisation as well as a bitmap showing a high-level view of the calltree. For further information about these topics please see the glossary for full calltree and calltree overview

Full calltree

Call tree overview bitmap:

The distribution of callsites in terms of coloring is
Color Runtime hitcount Callsite count Percentage
red 0 81 40.7%
gold [1:9] 0 0.0%
yellow [10:29] 0 0.0%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 118 59.2%
All colors 199 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
17 108 tomlkit._compat.decode call site: 00108 contextlib.suppress
11 164 tomlkit.items.Time.__init__ call site: 00164 builtins.list.isoformat
10 31 tomlkit.items.item call site: 00031 builtins.int.items
8 152 tomlkit.items.item call site: 00152 tomlkit.items.Date.__init__
7 93 tomlkit.items.item call site: 00093 numbers.Integral.items
7 144 tomlkit.items.DateTime.__init__ call site: 00144 builtins.list.isoformat
6 62 tomlkit.items.AoT.__init__ call site: 00062 tomlkit.items.item
3 43 tomlkit.items.item call site: 00043 .isinstance
3 193 tomlkit.items.Array.as_string call site: 00193 v.value.as_string
1 1 ...fuzz_dumps.test_one_input call site: 00001 fdp.ConsumeInt
1 24 tomlkit.items.item call site: 00024 .isinstance
1 50 tomlkit.items.Table.append call site: 00050 tomlkit.items.item

Runtime coverage analysis

Covered functions
270
Functions that are reachable but not covered
66
Reachable functions
98
Percentage of reachable functions covered
32.65%
NB: The sum of covered functions and functions that are reachable but not covered need not be equal to Reachable functions . This is because the reachability analysis is an approximation and thus at runtime some functions may be covered that are not included in the reachability analysis. This is a limitation of our static analysis capabilities.
Warning: The number of covered functions are larger than the number of reachable functions. This means that there are more functions covered at runtime than are extracted using static analysis. This is likely a result of the static analysis component failing to extract the right call graph or the coverage runtime being compiled with sanitizers in code that the static analysis has not analysed. This can happen if lto/gold is not used in all places that coverage instrumentation is used.
Function name source code lines source lines hit percentage hit

Files reached

filename functions hit
/ 1
...fuzz_dumps 4
tomlkit.api 18
tomlkit.items 63
tomlkit._compat 10
tomlkit._utils 7

Fuzzer: fuzz_parser

Call tree

The calltree shows the control flow of the fuzzer. This is overlaid with coverage information to display how much of the potential code a fuzzer can reach is in fact covered at runtime. In the following there is a link to a detailed calltree visualisation as well as a bitmap showing a high-level view of the calltree. For further information about these topics please see the glossary for full calltree and calltree overview

Full calltree

Call tree overview bitmap:

The distribution of callsites in terms of coloring is
Color Runtime hitcount Callsite count Percentage
red 0 157 20.7%
gold [1:9] 0 0.0%
yellow [10:29] 0 0.0%
greenyellow [30:49] 0 0.0%
lawngreen 50+ 598 79.2%
All colors 755 100

Fuzz blockers

The following nodes represent call sites where fuzz blockers occur.

Amount of callsites blocked Calltree index Parent function Callsite Largest blocked function
17 5 tomlkit._compat.decode call site: 00005 contextlib.suppress
12 470 tomlkit.container.Container._replace_at call site: 00470 tomlkit.items.InlineTable.append
11 276 tomlkit.items.item call site: 00276 builtins.int.items
11 362 tomlkit.items.Time.__init__ call site: 00362 builtins.list.isoformat
11 439 tomlkit.container.Container._replace_at call site: 00439 tomlkit.container.Container._insert_at
8 350 tomlkit.items.item call site: 00350 tomlkit.items.Date.__init__
7 320 tomlkit.items.item call site: 00320 datetime.time.items
7 342 tomlkit.items.DateTime.__init__ call site: 00342 builtins.list.isoformat
6 308 tomlkit.items.AoT.__init__ call site: 00308 tomlkit.items.item
6 702 tomlkit.parser.Parser._parse_table call site: 00702 tomlkit.items.Table.__init__
5 393 tomlkit.container.Container.append call site: 00393 .isinstance
4 433 tomlkit.container.Container._replace_at call site: 00433 tomlkit.items.SingleKey.__init__

Runtime coverage analysis

Covered functions
269
Functions that are reachable but not covered
117
Reachable functions
218
Percentage of reachable functions covered
46.33%
NB: The sum of covered functions and functions that are reachable but not covered need not be equal to Reachable functions . This is because the reachability analysis is an approximation and thus at runtime some functions may be covered that are not included in the reachability analysis. This is a limitation of our static analysis capabilities.
Warning: The number of covered functions are larger than the number of reachable functions. This means that there are more functions covered at runtime than are extracted using static analysis. This is likely a result of the static analysis component failing to extract the right call graph or the coverage runtime being compiled with sanitizers in code that the static analysis has not analysed. This can happen if lto/gold is not used in all places that coverage instrumentation is used.
Function name source code lines source lines hit percentage hit

Files reached

filename functions hit
/ 1
...fuzz_parser 4
tomlkit.parser 102
tomlkit._compat 10
tomlkit.source 10
tomlkit.toml_char 2
tomlkit.items 68
tomlkit._utils 19
tomlkit.container 61

Analyses and suggestions

Optimal target analysis

Remaining optimal interesting functions

The following table shows a list of functions that are optimal targets. Optimal targets are identified by finding the functions that in combination, yield a high code coverage.

Func name Functions filename Arg count Args Function depth hitcount instr count bb count cyclomatic complexity Reachable functions Incoming references total cyclomatic complexity Unreached complexity
tomlkit.container.Container.as_string tomlkit.container 1 ['N/A'] 4 0 1 5 5 26 0 90 48

Implementing fuzzers that target the above functions will improve reachability such that it becomes:

Functions statically reachable by fuzzers
27.0%
105 / 382
Cyclomatic complexity statically reachable by fuzzers
33.0%
428 / 1314

All functions overview

If you implement fuzzers for these functions, the status of all functions in the project will be:

Func name Functions filename Args Function call depth Reached by Fuzzers Runtime reached by Fuzzers Combined reached by Fuzzers Fuzzers runtime hit Func lines hit % I Count BB Count Cyclomatic complexity Functions reached Reached by functions Accumulated cyclomatic complexity Undiscovered complexity

Fuzz engine guidance

This sections provides heuristics that can be used as input to a fuzz engine when running a given fuzz target. The current focus is on providing input that is usable by libFuzzer.

/src/fuzz_dumps.py

Dictionary

Use this with the libFuzzer -dict=DICT.file flag


Fuzzer function priority

Use one of these functions as input to libfuzzer with flag: -focus_function name 

-focus_function=['tomlkit._compat.decode', 'tomlkit.items.Time.__init__', 'tomlkit.items.item', 'tomlkit.items.DateTime.__init__', 'tomlkit.items.AoT.__init__', 'tomlkit.items.Array.as_string', '...fuzz_dumps.test_one_input']

/src/fuzz_parser.py

Dictionary

Use this with the libFuzzer -dict=DICT.file flag


Fuzzer function priority

Use one of these functions as input to libfuzzer with flag: -focus_function name 

-focus_function=['tomlkit._compat.decode', 'tomlkit.container.Container._replace_at', 'tomlkit.items.item', 'tomlkit.items.Time.__init__', 'tomlkit.items.DateTime.__init__', 'tomlkit.items.AoT.__init__', 'tomlkit.parser.Parser._parse_table']

Runtime coverage analysis

This section shows analysis of runtime coverage data.

For futher technical details on how this section is generated, please see the Glossary .

Complex functions with low coverage

Func name Function total lines Lines covered at runtime percentage covered Reached by fuzzers
tomlkit.items.Array.add_line 39 0 0.0% []
tomlkit.items.Array.__delitem__ 43 0 0.0% []
tomlkit.items.InlineTable.as_string 31 15 48.38% ['fuzz_parser', 'fuzz_dumps']
tomlkit.container.Container._replace_at 40 16 40.0% ['fuzz_parser', 'fuzz_dumps']

Files and Directories in report

This section shows which files and directories are considered in this report. The main reason for showing this is fuzz introspector may include more code in the reasoning than is desired. This section helps identify if too many files/directories are included, e.g. third party code, which may be irrelevant for the threat model. In the event too much is included, fuzz introspector supports a configuration file that can exclude data from the report. See the following link for more information on how to create a config file: link

Files in report

Source file Reached by Covered by
[] []
tomlkit.toml_char ['fuzz_parser'] []
dictgen [] []
...fuzz_dumps ['fuzz_dumps'] []
re [] []
tomlkit._types [] []
tomlkit.api ['fuzz_dumps'] []
tomlkit.toml_document [] []
dictgen.generate [] []
numbers [] []
copy [] []
tomlkit.toml_file [] []
tomlkit.exceptions [] []
typing [] []
dictgen.utils [] []
tomlkit.source ['fuzz_parser'] []
tomlkit.parser ['fuzz_parser'] []
random [] []
tomlkit.items ['fuzz_dumps', 'fuzz_parser'] []
dataclasses [] []
...fuzz_parser ['fuzz_parser'] []
tomlkit._utils ['fuzz_dumps', 'fuzz_parser'] []
math [] []
abc [] []
atheris [] []
collections [] []
inspect [] []
tomlkit [] []
tomlkit._compat ['fuzz_dumps', 'fuzz_parser'] []
contextlib [] []
datetime [] []
[] []
tomlkit.container ['fuzz_parser'] []
builtins [] []

Directories in report

Directory

Metadata section

This sections shows the raw data that is used to produce this report. This is mainly used for further processing and developer debugging.

Fuzzer Calltree file Program data file Coverage file
fuzz_dumps fuzzerLogFile-fuzz_dumps.data fuzzerLogFile-fuzz_dumps.data.yaml all_cov.json
fuzz_parser fuzzerLogFile-fuzz_parser.data fuzzerLogFile-fuzz_parser.data.yaml all_cov.json